Initial reorg.

This is largely the same as #305, but updated for the current tree.

crates/runtime/Cargo.toml

@@ -0,0 +1,40 @@
+[package]
+name = "wasmtime-runtime"
+version = "0.2.0"
+authors = ["The Wasmtime Project Developers"]
+description = "Runtime library support for Wasmtime"
+categories = ["wasm"]
+keywords = ["webassembly", "wasm"]
+repository = "https://github.com/CraneStation/wasmtime"
+license = "Apache-2.0 WITH LLVM-exception"
+readme = "README.md"
+edition = "2018"
+
+[dependencies]
+cranelift-codegen = { version = "0.49", features = ["enable-serde"] }
+cranelift-entity = { version = "0.49", features = ["enable-serde"] }
+cranelift-wasm = { version = "0.49", features = ["enable-serde"] }
+wasmtime-environ = { path = "../environ", default-features = false }
+region = "2.0.0"
+lazy_static = "1.2.0"
+libc = { version = "0.2.60", default-features = false }
+memoffset = "0.5.1"
+indexmap = "1.0.2"
+hashbrown = { version = "0.6.0", optional = true }
+spin = { version = "0.5.2", optional = true }
+thiserror = "1.0.4"
+
+[target.'cfg(target_os = "windows")'.dependencies]
+winapi = { version = "0.3.7", features = ["winbase", "memoryapi"] }
+
+[build-dependencies]
+cc = "1.0"
+
+[features]
+default = ["std"]
+std = ["cranelift-codegen/std", "cranelift-wasm/std", "wasmtime-environ/std"]
+core = ["hashbrown/nightly", "cranelift-codegen/core", "cranelift-wasm/core", "wasmtime-environ/core", "spin"]
+
+[badges]
+maintenance = { status = "experimental" }
+travis-ci = { repository = "CraneStation/wasmtime" }

crates/runtime/LICENSE

@@ -0,0 +1,220 @@
+
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crates/runtime/README.md

@@ -0,0 +1,10 @@
+This is the `wasmtime-runtime` crate, which contains wasm runtime library
+support, supporting the wasm ABI used by [`wasmtime-environ`],
+[`wasmtime-jit`], and [`wasmtime-obj`].
+
+This crate does not make a host vs. target distinction; it is meant to be
+compiled for the target.
+
+[`wasmtime-environ`]: https://crates.io/crates/wasmtime-environ
+[`wasmtime-jit`]: https://crates.io/crates/wasmtime-jit
+[`wasmtime-obj`]: https://crates.io/crates/wasmtime-obj

crates/runtime/build.rs

@@ -0,0 +1,20 @@
+fn main() {
+    println!("cargo:rerun-if-changed=signalhandlers/SignalHandlers.cpp");
+    println!("cargo:rerun-if-changed=signalhandlers/SignalHandlers.hpp");
+    println!("cargo:rerun-if-changed=signalhandlers/Trampolines.cpp");
+    let target = std::env::var("TARGET").unwrap();
+    let mut build = cc::Build::new();
+    build
+        .cpp(true)
+        .warnings(false)
+        .file("signalhandlers/SignalHandlers.cpp")
+        .file("signalhandlers/Trampolines.cpp");
+    if !target.contains("windows") {
+        build
+            .flag("-std=c++11")
+            .flag("-fno-exceptions")
+            .flag("-fno-rtti");
+    }
+
+    build.compile("signalhandlers");
+}

crates/runtime/signalhandlers/SignalHandlers.cpp

@@ -0,0 +1,827 @@
+//! This file is largely derived from the code in WasmSignalHandlers.cpp in SpiderMonkey:
+//!
+//! https://dxr.mozilla.org/mozilla-central/source/js/src/wasm/WasmSignalHandlers.cpp
+//!
+//! Use of Mach ports on Darwin platforms (the USE_APPLE_MACH_PORTS code below) is
+//! currently disabled.
+
+#include "SignalHandlers.hpp"
+
+#include <stdint.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#if defined(_WIN32)
+
+# include <windows.h>
+# include <winternl.h>
+
+#elif defined(USE_APPLE_MACH_PORTS)
+# include <mach/exc.h>
+# include <mach/mach.h>
+# include <pthread.h>
+#else
+# include <signal.h>
+#endif
+
+// =============================================================================
+// This following pile of macros and includes defines the ToRegisterState() and
+// the ContextToPC() functions from the (highly) platform-specific CONTEXT
+// struct which is provided to the signal handler.
+// =============================================================================
+
+#if defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
+# include <sys/ucontext.h> // for ucontext_t, mcontext_t
+#endif
+
+#if defined(__x86_64__)
+# if defined(__DragonFly__)
+#  include <machine/npx.h> // for union savefpu
+# elif defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || \
+       defined(__NetBSD__) || defined(__OpenBSD__)
+#  include <machine/fpu.h> // for struct savefpu/fxsave64
+# endif
+#endif
+
+#if defined(_WIN32)
+# define EIP_sig(p) ((p)->Eip)
+# define EBP_sig(p) ((p)->Ebp)
+# define ESP_sig(p) ((p)->Esp)
+# define RIP_sig(p) ((p)->Rip)
+# define RSP_sig(p) ((p)->Rsp)
+# define RBP_sig(p) ((p)->Rbp)
+# define R11_sig(p) ((p)->R11)
+# define R13_sig(p) ((p)->R13)
+# define R14_sig(p) ((p)->R14)
+# define R15_sig(p) ((p)->R15)
+# define EPC_sig(p) ((p)->Pc)
+# define RFP_sig(p) ((p)->Fp)
+# define R31_sig(p) ((p)->Sp)
+# define RLR_sig(p) ((p)->Lr)
+#elif defined(__OpenBSD__)
+# define EIP_sig(p) ((p)->sc_eip)
+# define EBP_sig(p) ((p)->sc_ebp)
+# define ESP_sig(p) ((p)->sc_esp)
+# define RIP_sig(p) ((p)->sc_rip)
+# define RSP_sig(p) ((p)->sc_rsp)
+# define RBP_sig(p) ((p)->sc_rbp)
+# define R11_sig(p) ((p)->sc_r11)
+# if defined(__arm__)
+#  define R13_sig(p) ((p)->sc_usr_sp)
+#  define R14_sig(p) ((p)->sc_usr_lr)
+#  define R15_sig(p) ((p)->sc_pc)
+# else
+#  define R13_sig(p) ((p)->sc_r13)
+#  define R14_sig(p) ((p)->sc_r14)
+#  define R15_sig(p) ((p)->sc_r15)
+# endif
+# if defined(__aarch64__)
+#  define EPC_sig(p) ((p)->sc_elr)
+#  define RFP_sig(p) ((p)->sc_x[29])
+#  define RLR_sig(p) ((p)->sc_lr)
+#  define R31_sig(p) ((p)->sc_sp)
+# endif
+# if defined(__mips__)
+#  define EPC_sig(p) ((p)->sc_pc)
+#  define RFP_sig(p) ((p)->sc_regs[30])
+# endif
+#elif defined(__linux__) || defined(__sun)
+# if defined(__linux__)
+#  define EIP_sig(p) ((p)->uc_mcontext.gregs[REG_EIP])
+#  define EBP_sig(p) ((p)->uc_mcontext.gregs[REG_EBP])
+#  define ESP_sig(p) ((p)->uc_mcontext.gregs[REG_ESP])
+# else
+#  define EIP_sig(p) ((p)->uc_mcontext.gregs[REG_PC])
+#  define EBP_sig(p) ((p)->uc_mcontext.gregs[REG_EBP])
+#  define ESP_sig(p) ((p)->uc_mcontext.gregs[REG_ESP])
+# endif
+# define RIP_sig(p) ((p)->uc_mcontext.gregs[REG_RIP])
+# define RSP_sig(p) ((p)->uc_mcontext.gregs[REG_RSP])
+# define RBP_sig(p) ((p)->uc_mcontext.gregs[REG_RBP])
+# if defined(__linux__) && defined(__arm__)
+#  define R11_sig(p) ((p)->uc_mcontext.arm_fp)
+#  define R13_sig(p) ((p)->uc_mcontext.arm_sp)
+#  define R14_sig(p) ((p)->uc_mcontext.arm_lr)
+#  define R15_sig(p) ((p)->uc_mcontext.arm_pc)
+# else
+#  define R11_sig(p) ((p)->uc_mcontext.gregs[REG_R11])
+#  define R13_sig(p) ((p)->uc_mcontext.gregs[REG_R13])
+#  define R14_sig(p) ((p)->uc_mcontext.gregs[REG_R14])
+#  define R15_sig(p) ((p)->uc_mcontext.gregs[REG_R15])
+# endif
+# if defined(__linux__) && defined(__aarch64__)
+#  define EPC_sig(p) ((p)->uc_mcontext.pc)
+#  define RFP_sig(p) ((p)->uc_mcontext.regs[29])
+#  define RLR_sig(p) ((p)->uc_mcontext.regs[30])
+#  define R31_sig(p) ((p)->uc_mcontext.regs[31])
+# endif
+# if defined(__linux__) && defined(__mips__)
+#  define EPC_sig(p) ((p)->uc_mcontext.pc)
+#  define RFP_sig(p) ((p)->uc_mcontext.gregs[30])
+#  define RSP_sig(p) ((p)->uc_mcontext.gregs[29])
+#  define R31_sig(p) ((p)->uc_mcontext.gregs[31])
+# endif
+# if defined(__linux__) && (defined(__sparc__) && defined(__arch64__))
+#  define PC_sig(p) ((p)->uc_mcontext.mc_gregs[MC_PC])
+#  define FP_sig(p) ((p)->uc_mcontext.mc_fp)
+#  define SP_sig(p) ((p)->uc_mcontext.mc_i7)
+# endif
+# if defined(__linux__) && \
+     (defined(__ppc64__) ||  defined (__PPC64__) || defined(__ppc64le__) || defined (__PPC64LE__))
+#  define R01_sig(p) ((p)->uc_mcontext.gp_regs[1])
+#  define R32_sig(p) ((p)->uc_mcontext.gp_regs[32])
+# endif
+#elif defined(__NetBSD__)
+# define EIP_sig(p) ((p)->uc_mcontext.__gregs[_REG_EIP])
+# define EBP_sig(p) ((p)->uc_mcontext.__gregs[_REG_EBP])
+# define ESP_sig(p) ((p)->uc_mcontext.__gregs[_REG_ESP])
+# define RIP_sig(p) ((p)->uc_mcontext.__gregs[_REG_RIP])
+# define RSP_sig(p) ((p)->uc_mcontext.__gregs[_REG_RSP])
+# define RBP_sig(p) ((p)->uc_mcontext.__gregs[_REG_RBP])
+# define R11_sig(p) ((p)->uc_mcontext.__gregs[_REG_R11])
+# define R13_sig(p) ((p)->uc_mcontext.__gregs[_REG_R13])
+# define R14_sig(p) ((p)->uc_mcontext.__gregs[_REG_R14])
+# define R15_sig(p) ((p)->uc_mcontext.__gregs[_REG_R15])
+# if defined(__aarch64__)
+#  define EPC_sig(p) ((p)->uc_mcontext.__gregs[_REG_PC])
+#  define RFP_sig(p) ((p)->uc_mcontext.__gregs[_REG_X29])
+#  define RLR_sig(p) ((p)->uc_mcontext.__gregs[_REG_X30])
+#  define R31_sig(p) ((p)->uc_mcontext.__gregs[_REG_SP])
+# endif
+# if defined(__mips__)
+#  define EPC_sig(p) ((p)->uc_mcontext.__gregs[_REG_EPC])
+#  define RFP_sig(p) ((p)->uc_mcontext.__gregs[_REG_S8])
+# endif
+#elif defined(__DragonFly__) || defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
+# define EIP_sig(p) ((p)->uc_mcontext.mc_eip)
+# define EBP_sig(p) ((p)->uc_mcontext.mc_ebp)
+# define ESP_sig(p) ((p)->uc_mcontext.mc_esp)
+# define RIP_sig(p) ((p)->uc_mcontext.mc_rip)
+# define RSP_sig(p) ((p)->uc_mcontext.mc_rsp)
+# define RBP_sig(p) ((p)->uc_mcontext.mc_rbp)
+# if defined(__FreeBSD__) && defined(__arm__)
+#  define R11_sig(p) ((p)->uc_mcontext.__gregs[_REG_R11])
+#  define R13_sig(p) ((p)->uc_mcontext.__gregs[_REG_R13])
+#  define R14_sig(p) ((p)->uc_mcontext.__gregs[_REG_R14])
+#  define R15_sig(p) ((p)->uc_mcontext.__gregs[_REG_R15])
+# else
+#  define R11_sig(p) ((p)->uc_mcontext.mc_r11)
+#  define R13_sig(p) ((p)->uc_mcontext.mc_r13)
+#  define R14_sig(p) ((p)->uc_mcontext.mc_r14)
+#  define R15_sig(p) ((p)->uc_mcontext.mc_r15)
+# endif
+# if defined(__FreeBSD__) && defined(__aarch64__)
+#  define EPC_sig(p) ((p)->uc_mcontext.mc_gpregs.gp_elr)
+#  define RFP_sig(p) ((p)->uc_mcontext.mc_gpregs.gp_x[29])
+#  define RLR_sig(p) ((p)->uc_mcontext.mc_gpregs.gp_lr)
+#  define R31_sig(p) ((p)->uc_mcontext.mc_gpregs.gp_sp)
+# endif
+# if defined(__FreeBSD__) && defined(__mips__)
+#  define EPC_sig(p) ((p)->uc_mcontext.mc_pc)
+#  define RFP_sig(p) ((p)->uc_mcontext.mc_regs[30])
+# endif
+#elif defined(USE_APPLE_MACH_PORTS)
+# define EIP_sig(p) ((p)->thread.uts.ts32.__eip)
+# define EBP_sig(p) ((p)->thread.uts.ts32.__ebp)
+# define ESP_sig(p) ((p)->thread.uts.ts32.__esp)
+# define RIP_sig(p) ((p)->thread.__rip)
+# define RBP_sig(p) ((p)->thread.__rbp)
+# define RSP_sig(p) ((p)->thread.__rsp)
+# define R11_sig(p) ((p)->thread.__r[11])
+# define R13_sig(p) ((p)->thread.__sp)
+# define R14_sig(p) ((p)->thread.__lr)
+# define R15_sig(p) ((p)->thread.__pc)
+#elif defined(__APPLE__)
+# define EIP_sig(p) ((p)->uc_mcontext->__ss.__eip)
+# define EBP_sig(p) ((p)->uc_mcontext->__ss.__ebp)
+# define ESP_sig(p) ((p)->uc_mcontext->__ss.__esp)
+# define RIP_sig(p) ((p)->uc_mcontext->__ss.__rip)
+# define RBP_sig(p) ((p)->uc_mcontext->__ss.__rbp)
+# define RSP_sig(p) ((p)->uc_mcontext->__ss.__rsp)
+# define R11_sig(p) ((p)->uc_mcontext->__ss.__r11)
+# define R13_sig(p) ((p)->uc_mcontext->__ss.__sp)
+# define R14_sig(p) ((p)->uc_mcontext->__ss.__lr)
+# define R15_sig(p) ((p)->uc_mcontext->__ss.__pc)
+#else
+# error "Don't know how to read/write to the thread state via the mcontext_t."
+#endif
+
+#if defined(ANDROID)
+// Not all versions of the Android NDK define ucontext_t or mcontext_t.
+// Detect this and provide custom but compatible definitions. Note that these
+// follow the GLibc naming convention to access register values from
+// mcontext_t.
+//
+// See: https://chromiumcodereview.appspot.com/10829122/
+// See: http://code.google.com/p/android/issues/detail?id=34784
+# if !defined(__BIONIC_HAVE_UCONTEXT_T)
+#  if defined(__arm__)
+
+// GLibc on ARM defines mcontext_t has a typedef for 'struct sigcontext'.
+// Old versions of the C library <signal.h> didn't define the type.
+#   if !defined(__BIONIC_HAVE_STRUCT_SIGCONTEXT)
+#    include <asm/sigcontext.h>
+#   endif
+
+typedef struct sigcontext mcontext_t;
+
+typedef struct ucontext {
+    uint32_t uc_flags;
+    struct ucontext* uc_link;
+    stack_t uc_stack;
+    mcontext_t uc_mcontext;
+    // Other fields are not used so don't define them here.
+} ucontext_t;
+
+#  elif defined(__mips__)
+
+typedef struct {
+    uint32_t regmask;
+    uint32_t status;
+    uint64_t pc;
+    uint64_t gregs[32];
+    uint64_t fpregs[32];
+    uint32_t acx;
+    uint32_t fpc_csr;
+    uint32_t fpc_eir;
+    uint32_t used_math;
+    uint32_t dsp;
+    uint64_t mdhi;
+    uint64_t mdlo;
+    uint32_t hi1;
+    uint32_t lo1;
+    uint32_t hi2;
+    uint32_t lo2;
+    uint32_t hi3;
+    uint32_t lo3;
+} mcontext_t;
+
+typedef struct ucontext {
+    uint32_t uc_flags;
+    struct ucontext* uc_link;
+    stack_t uc_stack;
+    mcontext_t uc_mcontext;
+    // Other fields are not used so don't define them here.
+} ucontext_t;
+
+#  elif defined(__i386__)
+// x86 version for Android.
+typedef struct {
+    uint32_t gregs[19];
+    void* fpregs;
+    uint32_t oldmask;
+    uint32_t cr2;
+} mcontext_t;
+
+typedef uint32_t kernel_sigset_t[2];  // x86 kernel uses 64-bit signal masks
+typedef struct ucontext {
+    uint32_t uc_flags;
+    struct ucontext* uc_link;
+    stack_t uc_stack;
+    mcontext_t uc_mcontext;
+    // Other fields are not used by V8, don't define them here.
+} ucontext_t;
+enum { REG_EIP = 14 };
+#  endif  // defined(__i386__)
+# endif  // !defined(__BIONIC_HAVE_UCONTEXT_T)
+#endif // defined(ANDROID)
+
+#if defined(USE_APPLE_MACH_PORTS)
+# if defined(__x86_64__)
+struct macos_x64_context {
+    x86_thread_state64_t thread;
+    x86_float_state64_t float_;
+};
+#  define CONTEXT macos_x64_context
+# elif defined(__i386__)
+struct macos_x86_context {
+    x86_thread_state_t thread;
+    x86_float_state_t float_;
+};
+#  define CONTEXT macos_x86_context
+# elif defined(__arm__)
+struct macos_arm_context {
+    arm_thread_state_t thread;
+    arm_neon_state_t float_;
+};
+#  define CONTEXT macos_arm_context
+# else
+#  error Unsupported architecture
+# endif
+#elif !defined(_WIN32)
+# define CONTEXT ucontext_t
+#endif
+
+#if defined(_M_X64) || defined(__x86_64__)
+# define PC_sig(p) RIP_sig(p)
+# define FP_sig(p) RBP_sig(p)
+# define SP_sig(p) RSP_sig(p)
+#elif defined(_M_IX86) || defined(__i386__)
+# define PC_sig(p) EIP_sig(p)
+# define FP_sig(p) EBP_sig(p)
+# define SP_sig(p) ESP_sig(p)
+#elif defined(__arm__)
+# define FP_sig(p) R11_sig(p)
+# define SP_sig(p) R13_sig(p)
+# define LR_sig(p) R14_sig(p)
+# define PC_sig(p) R15_sig(p)
+#elif defined(_M_ARM64) || defined(__aarch64__)
+# define PC_sig(p) EPC_sig(p)
+# define FP_sig(p) RFP_sig(p)
+# define SP_sig(p) R31_sig(p)
+# define LR_sig(p) RLR_sig(p)
+#elif defined(__mips__)
+# define PC_sig(p) EPC_sig(p)
+# define FP_sig(p) RFP_sig(p)
+# define SP_sig(p) RSP_sig(p)
+# define LR_sig(p) R31_sig(p)
+#elif defined(__ppc64__) ||  defined (__PPC64__) || defined(__ppc64le__) || defined (__PPC64LE__)
+# define PC_sig(p) R32_sig(p)
+# define SP_sig(p) R01_sig(p)
+# define FP_sig(p) R01_sig(p)
+#endif
+
+static void
+SetContextPC(CONTEXT* context, const uint8_t* pc)
+{
+#ifdef PC_sig
+    PC_sig(context) = reinterpret_cast<uintptr_t>(pc);
+#else
+    abort();
+#endif
+}
+
+static const uint8_t*
+ContextToPC(CONTEXT* context)
+{
+#ifdef PC_sig
+    return reinterpret_cast<const uint8_t*>(static_cast<uintptr_t>(PC_sig(context)));
+#else
+    abort();
+#endif
+}
+
+// =============================================================================
+// All signals/exceptions funnel down to this one trap-handling function which
+// tests whether the pc is in a wasm module and, if so, whether there is
+// actually a trap expected at this pc. These tests both avoid real bugs being
+// silently converted to wasm traps and provides the trapping wasm bytecode
+// offset we need to report in the error.
+//
+// Crashing inside wasm trap handling (due to a bug in trap handling or exposed
+// during trap handling) must be reported like a normal crash, not cause the
+// crash report to be lost. On Windows and non-Mach Unix, a crash during the
+// handler reenters the handler, possibly repeatedly until exhausting the stack,
+// and so we prevent recursion with the thread-local sAlreadyHandlingTrap. On
+// Mach, the wasm exception handler has its own thread and is installed only on
+// the thread-level debugging ports of our threads, so a crash on
+// exception handler thread will not recurse; it will bubble up to the
+// process-level debugging ports (where Breakpad is installed).
+// =============================================================================
+
+static thread_local bool sAlreadyHandlingTrap;
+
+namespace {
+
+struct AutoHandlingTrap
+{
+    AutoHandlingTrap() {
+        assert(!sAlreadyHandlingTrap);
+        sAlreadyHandlingTrap = true;
+    }
+
+    ~AutoHandlingTrap() {
+        assert(sAlreadyHandlingTrap);
+        sAlreadyHandlingTrap = false;
+    }
+};
+
+}
+
+static
+#if defined(__GNUC__) || defined(__clang__)
+__attribute__ ((warn_unused_result))
+#endif
+bool
+HandleTrap(CONTEXT* context, bool reset_guard_page)
+{
+    assert(sAlreadyHandlingTrap);
+
+    if (!CheckIfTrapAtAddress(ContextToPC(context))) {
+        return false;
+    }
+
+    RecordTrap(ContextToPC(context), reset_guard_page);
+
+    // Unwind calls longjmp, so it doesn't run the automatic
+    // sAlreadhHanldingTrap cleanups, so reset it manually before doing
+    // a longjmp.
+    sAlreadyHandlingTrap = false;
+
+#if defined(USE_APPLE_MACH_PORTS)
+    // Reroute the PC to run the Unwind function on the main stack after the
+    // handler exits. This doesn't yet work for stack overflow traps, because
+    // in that case the main thread doesn't have any space left to run.
+    SetContextPC(context, reinterpret_cast<const uint8_t*>(&Unwind));
+#else
+    // For now, just call Unwind directly, rather than redirecting the PC there,
+    // so that it runs on the alternate signal handler stack. To run on the main
+    // stack, reroute the context PC like this:
+    Unwind();
+#endif
+
+    return true;
+}
+
+// =============================================================================
+// The following platform-specific handlers funnel all signals/exceptions into
+// the shared HandleTrap() above.
+// =============================================================================
+
+#if defined(_WIN32)
+// Obtained empirically from thread_local codegen on x86/x64/arm64.
+// Compiled in all user binaries, so should be stable over time.
+static const unsigned sThreadLocalArrayPointerIndex = 11;
+
+static LONG WINAPI
+WasmTrapHandler(LPEXCEPTION_POINTERS exception)
+{
+    // Make sure TLS is initialized before reading sAlreadyHandlingTrap.
+    if (!NtCurrentTeb()->Reserved1[sThreadLocalArrayPointerIndex]) {
+        return EXCEPTION_CONTINUE_SEARCH;
+    }
+
+    if (sAlreadyHandlingTrap) {
+        return EXCEPTION_CONTINUE_SEARCH;
+    }
+    AutoHandlingTrap aht;
+
+    EXCEPTION_RECORD* record = exception->ExceptionRecord;
+    if (record->ExceptionCode != EXCEPTION_ACCESS_VIOLATION &&
+        record->ExceptionCode != EXCEPTION_ILLEGAL_INSTRUCTION &&
+        record->ExceptionCode != EXCEPTION_STACK_OVERFLOW &&
+        record->ExceptionCode != EXCEPTION_INT_DIVIDE_BY_ZERO &&
+        record->ExceptionCode != EXCEPTION_INT_OVERFLOW)
+    {
+        return EXCEPTION_CONTINUE_SEARCH;
+    }
+
+    if (!HandleTrap(exception->ContextRecord,
+                    record->ExceptionCode == EXCEPTION_STACK_OVERFLOW)) {
+        return EXCEPTION_CONTINUE_SEARCH;
+    }
+
+    return EXCEPTION_CONTINUE_EXECUTION;
+}
+
+#elif defined(USE_APPLE_MACH_PORTS)
+// On OSX we are forced to use the lower-level Mach exception mechanism instead
+// of Unix signals because breakpad uses Mach exceptions and would otherwise
+// report a crash before wasm gets a chance to handle the exception.
+
+// This definition was generated by mig (the Mach Interface Generator) for the
+// routine 'exception_raise' (exc.defs).
+#pragma pack(4)
+typedef struct {
+    mach_msg_header_t Head;
+    /* start of the kernel processed data */
+    mach_msg_body_t msgh_body;
+    mach_msg_port_descriptor_t thread;
+    mach_msg_port_descriptor_t task;
+    /* end of the kernel processed data */
+    NDR_record_t NDR;
+    exception_type_t exception;
+    mach_msg_type_number_t codeCnt;
+    int64_t code[2];
+} Request__mach_exception_raise_t;
+#pragma pack()
+
+// The full Mach message also includes a trailer.
+struct ExceptionRequest
+{
+    Request__mach_exception_raise_t body;
+    mach_msg_trailer_t trailer;
+};
+
+static bool
+HandleMachException(const ExceptionRequest& request)
+{
+    // Get the port of the thread from the message.
+    mach_port_t cxThread = request.body.thread.name;
+
+    // Read out the thread's register state.
+    CONTEXT context;
+# if defined(__x86_64__)
+    unsigned int thread_state_count = x86_THREAD_STATE64_COUNT;
+    unsigned int float_state_count = x86_FLOAT_STATE64_COUNT;
+    int thread_state = x86_THREAD_STATE64;
+    int float_state = x86_FLOAT_STATE64;
+# elif defined(__i386__)
+    unsigned int thread_state_count = x86_THREAD_STATE_COUNT;
+    unsigned int float_state_count = x86_FLOAT_STATE_COUNT;
+    int thread_state = x86_THREAD_STATE;
+    int float_state = x86_FLOAT_STATE;
+# elif defined(__arm__)
+    unsigned int thread_state_count = ARM_THREAD_STATE_COUNT;
+    unsigned int float_state_count = ARM_NEON_STATE_COUNT;
+    int thread_state = ARM_THREAD_STATE;
+    int float_state = ARM_NEON_STATE;
+# else
+#  error Unsupported architecture
+# endif
+    kern_return_t kret;
+    kret = thread_get_state(cxThread, thread_state,
+                            (thread_state_t)&context.thread, &thread_state_count);
+    if (kret != KERN_SUCCESS) {
+        return false;
+    }
+    kret = thread_get_state(cxThread, float_state,
+                            (thread_state_t)&context.float_, &float_state_count);
+    if (kret != KERN_SUCCESS) {
+        return false;
+    }
+
+    if (request.body.exception != EXC_BAD_ACCESS &&
+        request.body.exception != EXC_BAD_INSTRUCTION)
+    {
+        return false;
+    }
+
+    {
+        AutoHandlingTrap aht;
+        if (!HandleTrap(&context, false)) {
+            return false;
+        }
+    }
+
+    // Update the thread state with the new pc and register values.
+    kret = thread_set_state(cxThread, float_state, (thread_state_t)&context.float_, float_state_count);
+    if (kret != KERN_SUCCESS) {
+        return false;
+    }
+    kret = thread_set_state(cxThread, thread_state, (thread_state_t)&context.thread, thread_state_count);
+    if (kret != KERN_SUCCESS) {
+        return false;
+    }
+
+    return true;
+}
+
+static mach_port_t sMachDebugPort = MACH_PORT_NULL;
+
+static void*
+MachExceptionHandlerThread(void* arg)
+{
+    // Taken from mach_exc in /usr/include/mach/mach_exc.defs.
+    static const unsigned EXCEPTION_MSG_ID = 2405;
+
+    while (true) {
+        ExceptionRequest request;
+        kern_return_t kret = mach_msg(&request.body.Head, MACH_RCV_MSG, 0, sizeof(request),
+                                      sMachDebugPort, MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL);
+
+        // If we fail even receiving the message, we can't even send a reply!
+        // Rather than hanging the faulting thread (hanging the browser), crash.
+        if (kret != KERN_SUCCESS) {
+            fprintf(stderr, "MachExceptionHandlerThread: mach_msg failed with %d\n", (int)kret);
+            abort();
+        }
+
+        if (request.body.Head.msgh_id != EXCEPTION_MSG_ID) {
+            fprintf(stderr, "Unexpected msg header id %d\n", (int)request.body.Head.msgh_bits);
+            abort();
+        }
+
+        // Some thread just commited an EXC_BAD_ACCESS and has been suspended by
+        // the kernel. The kernel is waiting for us to reply with instructions.
+        // Our default is the "not handled" reply (by setting the RetCode field
+        // of the reply to KERN_FAILURE) which tells the kernel to continue
+        // searching at the process and system level. If this is an
+        // expected exception, we handle it and return KERN_SUCCESS.
+        bool handled = HandleMachException(request);
+        kern_return_t replyCode = handled ? KERN_SUCCESS : KERN_FAILURE;
+
+        // This magic incantation to send a reply back to the kernel was
+        // derived from the exc_server generated by
+        // 'mig -v /usr/include/mach/mach_exc.defs'.
+        __Reply__exception_raise_t reply;
+        reply.Head.msgh_bits = MACH_MSGH_BITS(MACH_MSGH_BITS_REMOTE(request.body.Head.msgh_bits), 0);
+        reply.Head.msgh_size = sizeof(reply);
+        reply.Head.msgh_remote_port = request.body.Head.msgh_remote_port;
+        reply.Head.msgh_local_port = MACH_PORT_NULL;
+        reply.Head.msgh_id = request.body.Head.msgh_id + 100;
+        reply.NDR = NDR_record;
+        reply.RetCode = replyCode;
+        mach_msg(&reply.Head, MACH_SEND_MSG, sizeof(reply), 0, MACH_PORT_NULL,
+                 MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL);
+    }
+
+    return nullptr;
+}
+
+#else  // If not Windows or Mac, assume Unix
+
+static struct sigaction sPrevSIGSEGVHandler;
+static struct sigaction sPrevSIGBUSHandler;
+static struct sigaction sPrevSIGILLHandler;
+static struct sigaction sPrevSIGFPEHandler;
+
+static void
+WasmTrapHandler(int signum, siginfo_t* info, void* context)
+{
+    if (!sAlreadyHandlingTrap) {
+        AutoHandlingTrap aht;
+        assert(signum == SIGSEGV || signum == SIGBUS || signum == SIGFPE || signum == SIGILL);
+        if (HandleTrap(static_cast<CONTEXT*>(context), false)) {
+            return;
+        }
+    }
+
+    struct sigaction* previousSignal = nullptr;
+    switch (signum) {
+      case SIGSEGV: previousSignal = &sPrevSIGSEGVHandler; break;
+      case SIGBUS: previousSignal = &sPrevSIGBUSHandler; break;
+      case SIGFPE: previousSignal = &sPrevSIGFPEHandler; break;
+      case SIGILL: previousSignal = &sPrevSIGILLHandler; break;
+    }
+    assert(previousSignal);
+
+    // This signal is not for any compiled wasm code we expect, so we need to
+    // forward the signal to the next handler. If there is no next handler (SIG_IGN
+    // or SIG_DFL), then it's time to crash. To do this, we set the signal back to
+    // its original disposition and return. This will cause the faulting op to
+    // be re-executed which will crash in the normal way. The advantage of
+    // doing this to calling _exit() is that we remove ourselves from the crash
+    // stack which improves crash reports. If there is a next handler, call it.
+    // It will either crash synchronously, fix up the instruction so that
+    // execution can continue and return, or trigger a crash by returning the
+    // signal to it's original disposition and returning.
+    //
+    // Note: the order of these tests matter.
+    if (previousSignal->sa_flags & SA_SIGINFO) {
+        previousSignal->sa_sigaction(signum, info, context);
+    } else if (previousSignal->sa_handler == SIG_DFL || previousSignal->sa_handler == SIG_IGN) {
+        sigaction(signum, previousSignal, nullptr);
+    } else {
+        previousSignal->sa_handler(signum);
+    }
+}
+# endif // _WIN32 || __APPLE__ || assume unix
+
+#if defined(ANDROID) && defined(MOZ_LINKER)
+extern "C" MFBT_API bool IsSignalHandlingBroken();
+#endif
+
+int
+EnsureEagerSignalHandlers()
+{
+#if defined(ANDROID) && defined(MOZ_LINKER)
+    // Signal handling is broken on some android systems.
+    if (IsSignalHandlingBroken()) {
+        return false;
+    }
+#endif
+
+    sAlreadyHandlingTrap = false;
+
+    // Install whatever exception/signal handler is appropriate for the OS.
+#if defined(_WIN32)
+
+# if defined(MOZ_ASAN)
+    // Under ASan we need to let the ASan runtime's ShadowExceptionHandler stay
+    // in the first handler position. This requires some coordination with
+    // MemoryProtectionExceptionHandler::isDisabled().
+    const bool firstHandler = false;
+# else
+    // Otherwise, WasmTrapHandler needs to go first, so that we can recover
+    // from wasm faults and continue execution without triggering handlers
+    // such as MemoryProtectionExceptionHandler that assume we are crashing.
+    const bool firstHandler = true;
+# endif
+    if (!AddVectoredExceptionHandler(firstHandler, WasmTrapHandler)) {
+        // Windows has all sorts of random security knobs for disabling things
+        // so make this a dynamic failure that disables wasm, not an abort().
+        return false;
+    }
+
+#elif defined(USE_APPLE_MACH_PORTS)
+    // All the Mach setup in EnsureDarwinMachPorts.
+#else
+    // SA_ONSTACK allows us to handle signals on an alternate stack, so that
+    // the handler can run in response to running out of stack space on the
+    // main stack. Rust installs an alternate stack with sigaltstack, so we
+    // rely on that.
+
+    // SA_NODEFER allows us to reenter the signal handler if we crash while
+    // handling the signal, and fall through to the Breakpad handler by testing
+    // handlingSegFault.
+
+    // Allow handling OOB with signals on all architectures
+    struct sigaction faultHandler;
+    faultHandler.sa_flags = SA_SIGINFO | SA_NODEFER | SA_ONSTACK;
+    faultHandler.sa_sigaction = WasmTrapHandler;
+    sigemptyset(&faultHandler.sa_mask);
+    if (sigaction(SIGSEGV, &faultHandler, &sPrevSIGSEGVHandler)) {
+        perror("unable to install SIGSEGV handler");
+        abort();
+    }
+
+# if defined(__arm__) || defined(__APPLE__)
+    // On ARM, handle Unaligned Accesses.
+    // On Darwin, guard page accesses are raised as SIGBUS.
+    struct sigaction busHandler;
+    busHandler.sa_flags = SA_SIGINFO | SA_NODEFER | SA_ONSTACK;
+    busHandler.sa_sigaction = WasmTrapHandler;
+    sigemptyset(&busHandler.sa_mask);
+    if (sigaction(SIGBUS, &busHandler, &sPrevSIGBUSHandler)) {
+        perror("unable to install SIGBUS handler");
+        abort();
+    }
+# endif
+
+# if !defined(__mips__)
+    // Wasm traps for MIPS currently only raise integer overflow fp exception.
+    struct sigaction illHandler;
+    illHandler.sa_flags = SA_SIGINFO | SA_NODEFER | SA_ONSTACK;
+    illHandler.sa_sigaction = WasmTrapHandler;
+    sigemptyset(&illHandler.sa_mask);
+    if (sigaction(SIGILL, &illHandler, &sPrevSIGILLHandler)) {
+        perror("unable to install wasm SIGILL handler");
+        abort();
+    }
+# endif
+
+# if defined(__i386__) || defined(__x86_64__) || defined(__mips__)
+    // x86 uses SIGFPE to report division by zero, and wasm traps for MIPS
+    // currently raise integer overflow fp exception.
+    struct sigaction fpeHandler;
+    fpeHandler.sa_flags = SA_SIGINFO | SA_NODEFER | SA_ONSTACK;
+    fpeHandler.sa_sigaction = WasmTrapHandler;
+    sigemptyset(&fpeHandler.sa_mask);
+    if (sigaction(SIGFPE, &fpeHandler, &sPrevSIGFPEHandler)) {
+        perror("unable to install wasm SIGFPE handler");
+        abort();
+    }
+# endif
+
+#endif
+
+    return true;
+}
+
+int
+EnsureDarwinMachPorts()
+{
+#ifdef USE_APPLE_MACH_PORTS
+    pthread_attr_t handlerThreadAttr;
+    int r = pthread_attr_init(&handlerThreadAttr);
+    if (r != 0) {
+        return false;
+    }
+
+    // Create the port that all of our threads will redirect their traps to.
+    kern_return_t kret;
+    kret = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &sMachDebugPort);
+    if (kret != KERN_SUCCESS) {
+        return false;
+    }
+    kret = mach_port_insert_right(mach_task_self(), sMachDebugPort, sMachDebugPort,
+                                  MACH_MSG_TYPE_MAKE_SEND);
+    if (kret != KERN_SUCCESS) {
+        return false;
+    }
+
+    // Create the thread that will wait on and service sMachDebugPort.
+    // It's not useful to destroy this thread on process shutdown so
+    // immediately detach on successful start.
+    pthread_t handlerThread;
+    r = pthread_create(&handlerThread, &handlerThreadAttr, MachExceptionHandlerThread, nullptr);
+    if (r != 0) {
+        return false;
+    }
+    r = pthread_detach(handlerThread);
+    assert(r == 0);
+
+    // In addition to the process-wide signal handler setup, OSX needs each
+    // thread configured to send its exceptions to sMachDebugPort. While there
+    // are also task-level (i.e. process-level) exception ports, those are
+    // "claimed" by breakpad and chaining Mach exceptions is dark magic that we
+    // avoid by instead intercepting exceptions at the thread level before they
+    // propagate to the process-level. This works because there are no other
+    // uses of thread-level exception ports.
+    assert(sMachDebugPort != MACH_PORT_NULL);
+    thread_port_t thisThread = mach_thread_self();
+    kret = thread_set_exception_ports(thisThread,
+                                                    EXC_MASK_BAD_ACCESS | EXC_MASK_BAD_INSTRUCTION,
+                                                    sMachDebugPort,
+                                                    EXCEPTION_DEFAULT | MACH_EXCEPTION_CODES,
+                                                    THREAD_STATE_NONE);
+    mach_port_deallocate(mach_task_self(), thisThread);
+    if (kret != KERN_SUCCESS) {
+        return false;
+    }
+
+#endif
+    return true;
+}

crates/runtime/signalhandlers/SignalHandlers.hpp

@@ -0,0 +1,45 @@
+#ifndef signal_handlers_h
+#define signal_handlers_h
+
+#include <stdint.h>
+#include <setjmp.h>
+#ifndef __cplusplus
+#include <stdbool.h>
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int8_t CheckIfTrapAtAddress(const uint8_t* pc);
+// Record the Trap code and wasm bytecode offset in TLS somewhere
+void RecordTrap(const uint8_t* pc, bool reset_guard_page);
+
+void* EnterScope(void*);
+void LeaveScope(void*);
+void* GetScope(void);
+void Unwind(void);
+
+// This function performs the low-overhead signal handler initialization that we
+// want to do eagerly to ensure a more-deterministic global process state. This
+// is especially relevant for signal handlers since handler ordering depends on
+// installation order: the wasm signal handler must run *before* the other crash
+// handlers and since POSIX signal handlers work LIFO, this function needs to be
+// called at the end of the startup process, after other handlers have been
+// installed. This function can thus be called multiple times, having no effect
+// after the first call.
+int
+EnsureEagerSignalHandlers(void);
+
+// Assuming EnsureEagerProcessSignalHandlers() has already been called,
+// this function performs the full installation of signal handlers which must
+// be performed per-thread. This operation may incur some overhead and
+// so should be done only when needed to use wasm.
+int
+EnsureDarwinMachPorts(void);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+#endif // signal_handlers_h

crates/runtime/signalhandlers/Trampolines.cpp

@@ -0,0 +1,37 @@
+#include <setjmp.h>
+
+#include "SignalHandlers.hpp"
+
+extern "C"
+int WasmtimeCallTrampoline(void *vmctx, void (*body)(void*, void*), void *args) {
+  jmp_buf buf;
+  void *volatile prev;
+  if (setjmp(buf) != 0) {
+    LeaveScope(prev);
+    return 0;
+  }
+  prev = EnterScope(&buf);
+  body(vmctx, args);
+  LeaveScope(prev);
+  return 1;
+}
+
+extern "C"
+int WasmtimeCall(void *vmctx, void (*body)(void*)) {
+  jmp_buf buf;
+  void *volatile prev;
+  if (setjmp(buf) != 0) {
+    LeaveScope(prev);
+    return 0;
+  }
+  prev = EnterScope(&buf);
+  body(vmctx);
+  LeaveScope(prev);
+  return 1;
+}
+
+extern "C"
+void Unwind() {
+  jmp_buf *buf = (jmp_buf*) GetScope();
+  longjmp(*buf, 1);
+}

crates/runtime/src/export.rs

@@ -0,0 +1,104 @@
+use crate::vmcontext::{
+    VMContext, VMFunctionBody, VMGlobalDefinition, VMMemoryDefinition, VMTableDefinition,
+};
+use cranelift_codegen::ir;
+use cranelift_wasm::Global;
+use wasmtime_environ::{MemoryPlan, TablePlan};
+
+/// The value of an export passed from one instance to another.
+#[derive(Debug, Clone)]
+pub enum Export {
+    /// A function export value.
+    Function {
+        /// The address of the native-code function.
+        address: *const VMFunctionBody,
+        /// Pointer to the containing `VMContext`.
+        vmctx: *mut VMContext,
+        /// The function signature declaration, used for compatibilty checking.
+        signature: ir::Signature,
+    },
+
+    /// A table export value.
+    Table {
+        /// The address of the table descriptor.
+        definition: *mut VMTableDefinition,
+        /// Pointer to the containing `VMContext`.
+        vmctx: *mut VMContext,
+        /// The table declaration, used for compatibilty checking.
+        table: TablePlan,
+    },
+
+    /// A memory export value.
+    Memory {
+        /// The address of the memory descriptor.
+        definition: *mut VMMemoryDefinition,
+        /// Pointer to the containing `VMContext`.
+        vmctx: *mut VMContext,
+        /// The memory declaration, used for compatibilty checking.
+        memory: MemoryPlan,
+    },
+
+    /// A global export value.
+    Global {
+        /// The address of the global storage.
+        definition: *mut VMGlobalDefinition,
+        /// Pointer to the containing `VMContext`.
+        vmctx: *mut VMContext,
+        /// The global declaration, used for compatibilty checking.
+        global: Global,
+    },
+}
+
+impl Export {
+    /// Construct a function export value.
+    pub fn function(
+        address: *const VMFunctionBody,
+        vmctx: *mut VMContext,
+        signature: ir::Signature,
+    ) -> Self {
+        Self::Function {
+            address,
+            vmctx,
+            signature,
+        }
+    }
+
+    /// Construct a table export value.
+    pub fn table(
+        definition: *mut VMTableDefinition,
+        vmctx: *mut VMContext,
+        table: TablePlan,
+    ) -> Self {
+        Self::Table {
+            definition,
+            vmctx,
+            table,
+        }
+    }
+
+    /// Construct a memory export value.
+    pub fn memory(
+        definition: *mut VMMemoryDefinition,
+        vmctx: *mut VMContext,
+        memory: MemoryPlan,
+    ) -> Self {
+        Self::Memory {
+            definition,
+            vmctx,
+            memory,
+        }
+    }
+
+    /// Construct a global export value.
+    pub fn global(
+        definition: *mut VMGlobalDefinition,
+        vmctx: *mut VMContext,
+        global: Global,
+    ) -> Self {
+        Self::Global {
+            definition,
+            vmctx,
+            global,
+        }
+    }
+}

crates/runtime/src/imports.rs

@@ -0,0 +1,54 @@
+use crate::instance::InstanceHandle;
+use crate::vmcontext::{VMFunctionImport, VMGlobalImport, VMMemoryImport, VMTableImport};
+use crate::HashSet;
+use cranelift_entity::{BoxedSlice, PrimaryMap};
+use cranelift_wasm::{FuncIndex, GlobalIndex, MemoryIndex, TableIndex};
+
+/// Resolved import pointers.
+#[derive(Clone)]
+pub struct Imports {
+    /// The set of instances that the imports depend on.
+    pub dependencies: HashSet<InstanceHandle>,
+
+    /// Resolved addresses for imported functions.
+    pub functions: BoxedSlice<FuncIndex, VMFunctionImport>,
+
+    /// Resolved addresses for imported tables.
+    pub tables: BoxedSlice<TableIndex, VMTableImport>,
+
+    /// Resolved addresses for imported memories.
+    pub memories: BoxedSlice<MemoryIndex, VMMemoryImport>,
+
+    /// Resolved addresses for imported globals.
+    pub globals: BoxedSlice<GlobalIndex, VMGlobalImport>,
+}
+
+impl Imports {
+    /// Construct a new `Imports` instance.
+    pub fn new(
+        dependencies: HashSet<InstanceHandle>,
+        function_imports: PrimaryMap<FuncIndex, VMFunctionImport>,
+        table_imports: PrimaryMap<TableIndex, VMTableImport>,
+        memory_imports: PrimaryMap<MemoryIndex, VMMemoryImport>,
+        global_imports: PrimaryMap<GlobalIndex, VMGlobalImport>,
+    ) -> Self {
+        Self {
+            dependencies,
+            functions: function_imports.into_boxed_slice(),
+            tables: table_imports.into_boxed_slice(),
+            memories: memory_imports.into_boxed_slice(),
+            globals: global_imports.into_boxed_slice(),
+        }
+    }
+
+    /// Construct a new `Imports` instance with no imports.
+    pub fn none() -> Self {
+        Self {
+            dependencies: HashSet::new(),
+            functions: PrimaryMap::new().into_boxed_slice(),
+            tables: PrimaryMap::new().into_boxed_slice(),
+            memories: PrimaryMap::new().into_boxed_slice(),
+            globals: PrimaryMap::new().into_boxed_slice(),
+        }
+    }
+}

crates/runtime/src/jit_int.rs

@@ -0,0 +1,120 @@
+//! The GDB's JIT compilation interface. The low level module that exposes
+//! the __jit_debug_register_code() and __jit_debug_descriptor to register
+//! or unregister generated object images with debuggers.
+
+use alloc::boxed::Box;
+use alloc::vec::Vec;
+use core::ptr;
+
+#[repr(C)]
+struct JITCodeEntry {
+    next_entry: *mut JITCodeEntry,
+    prev_entry: *mut JITCodeEntry,
+    symfile_addr: *const u8,
+    symfile_size: u64,
+}
+
+const JIT_NOACTION: u32 = 0;
+const JIT_REGISTER_FN: u32 = 1;
+const JIT_UNREGISTER_FN: u32 = 2;
+
+#[repr(C)]
+struct JITDescriptor {
+    version: u32,
+    action_flag: u32,
+    relevant_entry: *mut JITCodeEntry,
+    first_entry: *mut JITCodeEntry,
+}
+
+#[no_mangle]
+#[used]
+static mut __jit_debug_descriptor: JITDescriptor = JITDescriptor {
+    version: 1,
+    action_flag: JIT_NOACTION,
+    relevant_entry: ptr::null_mut(),
+    first_entry: ptr::null_mut(),
+};
+
+#[no_mangle]
+#[inline(never)]
+extern "C" fn __jit_debug_register_code() {
+    // Hack to not allow inlining even when Rust wants to do it in release mode.
+    let x = 3;
+    unsafe {
+        core::ptr::read_volatile(&x);
+    }
+}
+
+/// Registeration for JIT image
+pub struct GdbJitImageRegistration {
+    entry: *mut JITCodeEntry,
+    file: Vec<u8>,
+}
+
+impl GdbJitImageRegistration {
+    /// Registers JIT image using __jit_debug_register_code
+    pub fn register(file: Vec<u8>) -> Self {
+        Self {
+            entry: unsafe { register_gdb_jit_image(&file) },
+            file,
+        }
+    }
+
+    /// JIT image used in registration
+    pub fn file(&self) -> &[u8] {
+        &self.file
+    }
+}
+
+impl Drop for GdbJitImageRegistration {
+    fn drop(&mut self) {
+        unsafe {
+            unregister_gdb_jit_image(self.entry);
+        }
+    }
+}
+
+unsafe fn register_gdb_jit_image(file: &[u8]) -> *mut JITCodeEntry {
+    // Create a code entry for the file, which gives the start and size of the symbol file.
+    let entry = Box::into_raw(Box::new(JITCodeEntry {
+        next_entry: __jit_debug_descriptor.first_entry,
+        prev_entry: ptr::null_mut(),
+        symfile_addr: file.as_ptr(),
+        symfile_size: file.len() as u64,
+    }));
+    // Add it to the linked list in the JIT descriptor.
+    if !__jit_debug_descriptor.first_entry.is_null() {
+        (*__jit_debug_descriptor.first_entry).prev_entry = entry;
+    }
+    __jit_debug_descriptor.first_entry = entry;
+    // Point the relevant_entry field of the descriptor at the entry.
+    __jit_debug_descriptor.relevant_entry = entry;
+    // Set action_flag to JIT_REGISTER and call __jit_debug_register_code.
+    __jit_debug_descriptor.action_flag = JIT_REGISTER_FN;
+    __jit_debug_register_code();
+
+    __jit_debug_descriptor.action_flag = JIT_NOACTION;
+    __jit_debug_descriptor.relevant_entry = ptr::null_mut();
+    entry
+}
+
+unsafe fn unregister_gdb_jit_image(entry: *mut JITCodeEntry) {
+    // Remove the code entry corresponding to the code from the linked list.
+    if !(*entry).prev_entry.is_null() {
+        (*(*entry).prev_entry).next_entry = (*entry).next_entry;
+    } else {
+        __jit_debug_descriptor.first_entry = (*entry).next_entry;
+    }
+    if !(*entry).next_entry.is_null() {
+        (*(*entry).next_entry).prev_entry = (*entry).prev_entry;
+    }
+    // Point the relevant_entry field of the descriptor at the code entry.
+    __jit_debug_descriptor.relevant_entry = entry;
+    // Set action_flag to JIT_UNREGISTER and call __jit_debug_register_code.
+    __jit_debug_descriptor.action_flag = JIT_UNREGISTER_FN;
+    __jit_debug_register_code();
+
+    __jit_debug_descriptor.action_flag = JIT_NOACTION;
+    __jit_debug_descriptor.relevant_entry = ptr::null_mut();
+    let _box = Box::from_raw(entry);
+}

crates/runtime/src/lib.rs

@@ -0,0 +1,73 @@
+//! Runtime library support for Wasmtime.
+
+#![deny(missing_docs, trivial_numeric_casts, unused_extern_crates)]
+#![warn(unused_import_braces)]
+#![cfg_attr(feature = "std", deny(unstable_features))]
+#![cfg_attr(feature = "clippy", plugin(clippy(conf_file = "../../clippy.toml")))]
+#![cfg_attr(
+    feature = "cargo-clippy",
+    allow(clippy::new_without_default, clippy::new_without_default_derive)
+)]
+#![cfg_attr(
+    feature = "cargo-clippy",
+    warn(
+        clippy::float_arithmetic,
+        clippy::mut_mut,
+        clippy::nonminimal_bool,
+        clippy::option_map_unwrap_or,
+        clippy::option_map_unwrap_or_else,
+        clippy::print_stdout,
+        clippy::unicode_not_nfc,
+        clippy::use_self
+    )
+)]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[macro_use]
+extern crate lazy_static;
+#[macro_use]
+extern crate memoffset;
+extern crate alloc;
+
+mod export;
+mod imports;
+mod instance;
+mod jit_int;
+mod memory;
+mod mmap;
+mod sig_registry;
+mod signalhandlers;
+mod table;
+mod trap_registry;
+mod traphandlers;
+mod vmcontext;
+
+pub mod libcalls;
+
+pub use crate::export::Export;
+pub use crate::imports::Imports;
+pub use crate::instance::{InstanceHandle, InstantiationError, LinkError};
+pub use crate::jit_int::GdbJitImageRegistration;
+pub use crate::mmap::Mmap;
+pub use crate::sig_registry::SignatureRegistry;
+pub use crate::signalhandlers::{wasmtime_init_eager, wasmtime_init_finish};
+pub use crate::trap_registry::{get_mut_trap_registry, get_trap_registry, TrapRegistrationGuard};
+pub use crate::traphandlers::{wasmtime_call, wasmtime_call_trampoline};
+pub use crate::vmcontext::{
+    VMCallerCheckedAnyfunc, VMContext, VMFunctionBody, VMFunctionImport, VMGlobalDefinition,
+    VMGlobalImport, VMInvokeArgument, VMMemoryDefinition, VMMemoryImport, VMSharedSignatureIndex,
+    VMTableDefinition, VMTableImport,
+};
+
+#[cfg(not(feature = "std"))]
+use hashbrown::{hash_map, HashMap, HashSet};
+#[cfg(feature = "std")]
+use std::collections::{hash_map, HashMap, HashSet};
+
+#[cfg(not(feature = "std"))]
+use spin::{RwLock, RwLockReadGuard, RwLockWriteGuard};
+#[cfg(feature = "std")]
+use std::sync::{RwLock, RwLockReadGuard, RwLockWriteGuard};
+
+/// Version number of this crate.
+pub const VERSION: &str = env!("CARGO_PKG_VERSION");

crates/runtime/src/libcalls.rs

@@ -0,0 +1,139 @@
+//! Runtime library calls. Note that wasm compilers may sometimes perform these
+//! inline rather than calling them, particularly when CPUs have special
+//! instructions which compute them directly.
+
+use crate::vmcontext::VMContext;
+use cranelift_wasm::{DefinedMemoryIndex, MemoryIndex};
+
+/// Implementation of f32.ceil
+pub extern "C" fn wasmtime_f32_ceil(x: f32) -> f32 {
+    x.ceil()
+}
+
+/// Implementation of f32.floor
+pub extern "C" fn wasmtime_f32_floor(x: f32) -> f32 {
+    x.floor()
+}
+
+/// Implementation of f32.trunc
+pub extern "C" fn wasmtime_f32_trunc(x: f32) -> f32 {
+    x.trunc()
+}
+
+/// Implementation of f32.nearest
+#[allow(clippy::float_arithmetic, clippy::float_cmp)]
+pub extern "C" fn wasmtime_f32_nearest(x: f32) -> f32 {
+    // Rust doesn't have a nearest function, so do it manually.
+    if x == 0.0 {
+        // Preserve the sign of zero.
+        x
+    } else {
+        // Nearest is either ceil or floor depending on which is nearest or even.
+        let u = x.ceil();
+        let d = x.floor();
+        let um = (x - u).abs();
+        let dm = (x - d).abs();
+        if um < dm
+            || (um == dm && {
+                let h = u / 2.;
+                h.floor() == h
+            })
+        {
+            u
+        } else {
+            d
+        }
+    }
+}
+
+/// Implementation of f64.ceil
+pub extern "C" fn wasmtime_f64_ceil(x: f64) -> f64 {
+    x.ceil()
+}
+
+/// Implementation of f64.floor
+pub extern "C" fn wasmtime_f64_floor(x: f64) -> f64 {
+    x.floor()
+}
+
+/// Implementation of f64.trunc
+pub extern "C" fn wasmtime_f64_trunc(x: f64) -> f64 {
+    x.trunc()
+}
+
+/// Implementation of f64.nearest
+#[allow(clippy::float_arithmetic, clippy::float_cmp)]
+pub extern "C" fn wasmtime_f64_nearest(x: f64) -> f64 {
+    // Rust doesn't have a nearest function, so do it manually.
+    if x == 0.0 {
+        // Preserve the sign of zero.
+        x
+    } else {
+        // Nearest is either ceil or floor depending on which is nearest or even.
+        let u = x.ceil();
+        let d = x.floor();
+        let um = (x - u).abs();
+        let dm = (x - d).abs();
+        if um < dm
+            || (um == dm && {
+                let h = u / 2.;
+                h.floor() == h
+            })
+        {
+            u
+        } else {
+            d
+        }
+    }
+}
+
+/// Implementation of memory.grow for locally-defined 32-bit memories.
+#[no_mangle]
+pub unsafe extern "C" fn wasmtime_memory32_grow(
+    vmctx: *mut VMContext,
+    delta: u32,
+    memory_index: u32,
+) -> u32 {
+    let instance = (&mut *vmctx).instance();
+    let memory_index = DefinedMemoryIndex::from_u32(memory_index);
+
+    instance
+        .memory_grow(memory_index, delta)
+        .unwrap_or(u32::max_value())
+}
+
+/// Implementation of memory.grow for imported 32-bit memories.
+#[no_mangle]
+pub unsafe extern "C" fn wasmtime_imported_memory32_grow(
+    vmctx: *mut VMContext,
+    delta: u32,
+    memory_index: u32,
+) -> u32 {
+    let instance = (&mut *vmctx).instance();
+    let memory_index = MemoryIndex::from_u32(memory_index);
+
+    instance
+        .imported_memory_grow(memory_index, delta)
+        .unwrap_or(u32::max_value())
+}
+
+/// Implementation of memory.size for locally-defined 32-bit memories.
+#[no_mangle]
+pub unsafe extern "C" fn wasmtime_memory32_size(vmctx: *mut VMContext, memory_index: u32) -> u32 {
+    let instance = (&mut *vmctx).instance();
+    let memory_index = DefinedMemoryIndex::from_u32(memory_index);
+
+    instance.memory_size(memory_index)
+}
+
+/// Implementation of memory.size for imported 32-bit memories.
+#[no_mangle]
+pub unsafe extern "C" fn wasmtime_imported_memory32_size(
+    vmctx: *mut VMContext,
+    memory_index: u32,
+) -> u32 {
+    let instance = (&mut *vmctx).instance();
+    let memory_index = MemoryIndex::from_u32(memory_index);
+
+    instance.imported_memory_size(memory_index)
+}

crates/runtime/src/memory.rs

@@ -0,0 +1,143 @@
+//! Memory management for linear memories.
+//!
+//! `LinearMemory` is to WebAssembly linear memories what `Table` is to WebAssembly tables.
+
+use crate::mmap::Mmap;
+use crate::vmcontext::VMMemoryDefinition;
+use alloc::string::String;
+use core::convert::TryFrom;
+use wasmtime_environ::{MemoryPlan, MemoryStyle, WASM_MAX_PAGES, WASM_PAGE_SIZE};
+
+/// A linear memory instance.
+#[derive(Debug)]
+pub struct LinearMemory {
+    // The underlying allocation.
+    mmap: Mmap,
+
+    // The current logical size in wasm pages of this linear memory.
+    current: u32,
+
+    // The optional maximum size in wasm pages of this linear memory.
+    maximum: Option<u32>,
+
+    // Size in bytes of extra guard pages after the end to optimize loads and stores with
+    // constant offsets.
+    offset_guard_size: usize,
+
+    // Records whether we're using a bounds-checking strategy which requires
+    // handlers to catch trapping accesses.
+    pub(crate) needs_signal_handlers: bool,
+}
+
+impl LinearMemory {
+    /// Create a new linear memory instance with specified minimum and maximum number of wasm pages.
+    pub fn new(plan: &MemoryPlan) -> Result<Self, String> {
+        // `maximum` cannot be set to more than `65536` pages.
+        assert!(plan.memory.minimum <= WASM_MAX_PAGES);
+        assert!(plan.memory.maximum.is_none() || plan.memory.maximum.unwrap() <= WASM_MAX_PAGES);
+
+        let offset_guard_bytes = plan.offset_guard_size as usize;
+
+        // If we have an offset guard, or if we're doing the static memory
+        // allocation strategy, we need signal handlers to catch out of bounds
+        // acceses.
+        let needs_signal_handlers = offset_guard_bytes > 0
+            || match plan.style {
+                MemoryStyle::Dynamic => false,
+                MemoryStyle::Static { .. } => true,
+            };
+
+        let minimum_pages = match plan.style {
+            MemoryStyle::Dynamic => plan.memory.minimum,
+            MemoryStyle::Static { bound } => {
+                assert!(bound >= plan.memory.minimum);
+                bound
+            }
+        } as usize;
+        let minimum_bytes = minimum_pages.checked_mul(WASM_PAGE_SIZE as usize).unwrap();
+        let request_bytes = minimum_bytes.checked_add(offset_guard_bytes).unwrap();
+        let mapped_pages = plan.memory.minimum as usize;
+        let mapped_bytes = mapped_pages * WASM_PAGE_SIZE as usize;
+
+        let mmap = Mmap::accessible_reserved(mapped_bytes, request_bytes)?;
+
+        Ok(Self {
+            mmap,
+            current: plan.memory.minimum,
+            maximum: plan.memory.maximum,
+            offset_guard_size: offset_guard_bytes,
+            needs_signal_handlers,
+        })
+    }
+
+    /// Returns the number of allocated wasm pages.
+    pub fn size(&self) -> u32 {
+        self.current
+    }
+
+    /// Grow memory by the specified amount of wasm pages.
+    ///
+    /// Returns `None` if memory can't be grown by the specified amount
+    /// of wasm pages.
+    pub fn grow(&mut self, delta: u32) -> Option<u32> {
+        // Optimization of memory.grow 0 calls.
+        if delta == 0 {
+            return Some(self.current);
+        }
+
+        let new_pages = match self.current.checked_add(delta) {
+            Some(new_pages) => new_pages,
+            // Linear memory size overflow.
+            None => return None,
+        };
+        let prev_pages = self.current;
+
+        if let Some(maximum) = self.maximum {
+            if new_pages > maximum {
+                // Linear memory size would exceed the declared maximum.
+                return None;
+            }
+        }
+
+        // Wasm linear memories are never allowed to grow beyond what is
+        // indexable. If the memory has no maximum, enforce the greatest
+        // limit here.
+        if new_pages >= WASM_MAX_PAGES {
+            // Linear memory size would exceed the index range.
+            return None;
+        }
+
+        let delta_bytes = usize::try_from(delta).unwrap() * WASM_PAGE_SIZE as usize;
+        let prev_bytes = usize::try_from(prev_pages).unwrap() * WASM_PAGE_SIZE as usize;
+        let new_bytes = usize::try_from(new_pages).unwrap() * WASM_PAGE_SIZE as usize;
+
+        if new_bytes > self.mmap.len() - self.offset_guard_size {
+            // If the new size is within the declared maximum, but needs more memory than we
+            // have on hand, it's a dynamic heap and it can move.
+            let guard_bytes = self.offset_guard_size;
+            let request_bytes = new_bytes.checked_add(guard_bytes)?;
+
+            let mut new_mmap = Mmap::accessible_reserved(new_bytes, request_bytes).ok()?;
+
+            let copy_len = self.mmap.len() - self.offset_guard_size;
+            new_mmap.as_mut_slice()[..copy_len].copy_from_slice(&self.mmap.as_slice()[..copy_len]);
+
+            self.mmap = new_mmap;
+        } else if delta_bytes > 0 {
+            // Make the newly allocated pages accessible.
+            self.mmap.make_accessible(prev_bytes, delta_bytes).ok()?;
+        }
+
+        self.current = new_pages;
+
+        Some(prev_pages)
+    }
+
+    /// Return a `VMMemoryDefinition` for exposing the memory to compiled wasm code.
+    pub fn vmmemory(&mut self) -> VMMemoryDefinition {
+        VMMemoryDefinition {
+            base: self.mmap.as_mut_ptr(),
+            current_length: self.current as usize * WASM_PAGE_SIZE as usize,
+        }
+    }
+}

crates/runtime/src/mmap.rs

@@ -0,0 +1,275 @@
+//! Low-level abstraction for allocating and managing zero-filled pages
+//! of memory.
+
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::ptr;
+use core::slice;
+#[cfg(not(target_os = "windows"))]
+use libc;
+use region;
+use std::io;
+
+/// Round `size` up to the nearest multiple of `page_size`.
+fn round_up_to_page_size(size: usize, page_size: usize) -> usize {
+    (size + (page_size - 1)) & !(page_size - 1)
+}
+
+/// A simple struct consisting of a page-aligned pointer to page-aligned
+/// and initially-zeroed memory and a length.
+#[derive(Debug)]
+pub struct Mmap {
+    ptr: *mut u8,
+    len: usize,
+}
+
+impl Mmap {
+    /// Construct a new empty instance of `Mmap`.
+    pub fn new() -> Self {
+        // Rust's slices require non-null pointers, even when empty. `Vec`
+        // contains code to create a non-null dangling pointer value when
+        // constructed empty, so we reuse that here.
+        Self {
+            ptr: Vec::new().as_mut_ptr(),
+            len: 0,
+        }
+    }
+
+    /// Create a new `Mmap` pointing to at least `size` bytes of page-aligned accessible memory.
+    pub fn with_at_least(size: usize) -> Result<Self, String> {
+        let page_size = region::page::size();
+        let rounded_size = round_up_to_page_size(size, page_size);
+        Self::accessible_reserved(rounded_size, rounded_size)
+    }
+
+    /// Create a new `Mmap` pointing to `accessible_size` bytes of page-aligned accessible memory,
+    /// within a reserved mapping of `mapping_size` bytes. `accessible_size` and `mapping_size`
+    /// must be native page-size multiples.
+    #[cfg(not(target_os = "windows"))]
+    pub fn accessible_reserved(
+        accessible_size: usize,
+        mapping_size: usize,
+    ) -> Result<Self, String> {
+        let page_size = region::page::size();
+        assert!(accessible_size <= mapping_size);
+        assert_eq!(mapping_size & (page_size - 1), 0);
+        assert_eq!(accessible_size & (page_size - 1), 0);
+
+        // Mmap may return EINVAL if the size is zero, so just
+        // special-case that.
+        if mapping_size == 0 {
+            return Ok(Self::new());
+        }
+
+        Ok(if accessible_size == mapping_size {
+            // Allocate a single read-write region at once.
+            let ptr = unsafe {
+                libc::mmap(
+                    ptr::null_mut(),
+                    mapping_size,
+                    libc::PROT_READ | libc::PROT_WRITE,
+                    libc::MAP_PRIVATE | libc::MAP_ANON,
+                    -1,
+                    0,
+                )
+            };
+            if ptr as isize == -1_isize {
+                return Err(io::Error::last_os_error().to_string());
+            }
+
+            Self {
+                ptr: ptr as *mut u8,
+                len: mapping_size,
+            }
+        } else {
+            // Reserve the mapping size.
+            let ptr = unsafe {
+                libc::mmap(
+                    ptr::null_mut(),
+                    mapping_size,
+                    libc::PROT_NONE,
+                    libc::MAP_PRIVATE | libc::MAP_ANON,
+                    -1,
+                    0,
+                )
+            };
+            if ptr as isize == -1_isize {
+                return Err(io::Error::last_os_error().to_string());
+            }
+
+            let mut result = Self {
+                ptr: ptr as *mut u8,
+                len: mapping_size,
+            };
+
+            if accessible_size != 0 {
+                // Commit the accessible size.
+                result.make_accessible(0, accessible_size)?;
+            }
+
+            result
+        })
+    }
+
+    /// Create a new `Mmap` pointing to `accessible_size` bytes of page-aligned accessible memory,
+    /// within a reserved mapping of `mapping_size` bytes. `accessible_size` and `mapping_size`
+    /// must be native page-size multiples.
+    #[cfg(target_os = "windows")]
+    pub fn accessible_reserved(
+        accessible_size: usize,
+        mapping_size: usize,
+    ) -> Result<Self, String> {
+        use winapi::um::memoryapi::VirtualAlloc;
+        use winapi::um::winnt::{MEM_COMMIT, MEM_RESERVE, PAGE_NOACCESS, PAGE_READWRITE};
+
+        let page_size = region::page::size();
+        assert!(accessible_size <= mapping_size);
+        assert_eq!(mapping_size & (page_size - 1), 0);
+        assert_eq!(accessible_size & (page_size - 1), 0);
+
+        Ok(if accessible_size == mapping_size {
+            // Allocate a single read-write region at once.
+            let ptr = unsafe {
+                VirtualAlloc(
+                    ptr::null_mut(),
+                    mapping_size,
+                    MEM_RESERVE | MEM_COMMIT,
+                    PAGE_READWRITE,
+                )
+            };
+            if ptr.is_null() {
+                return Err(io::Error::last_os_error().to_string());
+            }
+
+            Self {
+                ptr: ptr as *mut u8,
+                len: mapping_size,
+            }
+        } else {
+            // Reserve the mapping size.
+            let ptr =
+                unsafe { VirtualAlloc(ptr::null_mut(), mapping_size, MEM_RESERVE, PAGE_NOACCESS) };
+            if ptr.is_null() {
+                return Err(io::Error::last_os_error().to_string());
+            }
+
+            let mut result = Self {
+                ptr: ptr as *mut u8,
+                len: mapping_size,
+            };
+
+            if accessible_size != 0 {
+                // Commit the accessible size.
+                result.make_accessible(0, accessible_size)?;
+            }
+
+            result
+        })
+    }
+
+    /// Make the memory starting at `start` and extending for `len` bytes accessible.
+    /// `start` and `len` must be native page-size multiples and describe a range within
+    /// `self`'s reserved memory.
+    #[cfg(not(target_os = "windows"))]
+    pub fn make_accessible(&mut self, start: usize, len: usize) -> Result<(), String> {
+        let page_size = region::page::size();
+        assert_eq!(start & (page_size - 1), 0);
+        assert_eq!(len & (page_size - 1), 0);
+        assert!(len < self.len);
+        assert!(start < self.len - len);
+
+        // Commit the accessible size.
+        unsafe { region::protect(self.ptr.add(start), len, region::Protection::ReadWrite) }
+            .map_err(|e| e.to_string())
+    }
+
+    /// Make the memory starting at `start` and extending for `len` bytes accessible.
+    /// `start` and `len` must be native page-size multiples and describe a range within
+    /// `self`'s reserved memory.
+    #[cfg(target_os = "windows")]
+    pub fn make_accessible(&mut self, start: usize, len: usize) -> Result<(), String> {
+        use winapi::ctypes::c_void;
+        use winapi::um::memoryapi::VirtualAlloc;
+        use winapi::um::winnt::{MEM_COMMIT, PAGE_READWRITE};
+        let page_size = region::page::size();
+        assert_eq!(start & (page_size - 1), 0);
+        assert_eq!(len & (page_size - 1), 0);
+        assert!(len < self.len);
+        assert!(start < self.len - len);
+
+        // Commit the accessible size.
+        if unsafe {
+            VirtualAlloc(
+                self.ptr.add(start) as *mut c_void,
+                len,
+                MEM_COMMIT,
+                PAGE_READWRITE,
+            )
+        }
+        .is_null()
+        {
+            return Err(io::Error::last_os_error().to_string());
+        }
+
+        Ok(())
+    }
+
+    /// Return the allocated memory as a slice of u8.
+    pub fn as_slice(&self) -> &[u8] {
+        unsafe { slice::from_raw_parts(self.ptr, self.len) }
+    }
+
+    /// Return the allocated memory as a mutable slice of u8.
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        unsafe { slice::from_raw_parts_mut(self.ptr, self.len) }
+    }
+
+    /// Return the allocated memory as a pointer to u8.
+    pub fn as_ptr(&self) -> *const u8 {
+        self.ptr
+    }
+
+    /// Return the allocated memory as a mutable pointer to u8.
+    pub fn as_mut_ptr(&mut self) -> *mut u8 {
+        self.ptr
+    }
+
+    /// Return the length of the allocated memory.
+    pub fn len(&self) -> usize {
+        self.len
+    }
+}
+
+impl Drop for Mmap {
+    #[cfg(not(target_os = "windows"))]
+    fn drop(&mut self) {
+        if self.len != 0 {
+            let r = unsafe { libc::munmap(self.ptr as *mut libc::c_void, self.len) };
+            assert_eq!(r, 0, "munmap failed: {}", io::Error::last_os_error());
+        }
+    }
+
+    #[cfg(target_os = "windows")]
+    fn drop(&mut self) {
+        if self.len != 0 {
+            use winapi::ctypes::c_void;
+            use winapi::um::memoryapi::VirtualFree;
+            use winapi::um::winnt::MEM_RELEASE;
+            let r = unsafe { VirtualFree(self.ptr as *mut c_void, self.len, MEM_RELEASE) };
+            assert_eq!(r, 0);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_round_up_to_page_size() {
+        assert_eq!(round_up_to_page_size(0, 4096), 0);
+        assert_eq!(round_up_to_page_size(1, 4096), 4096);
+        assert_eq!(round_up_to_page_size(4096, 4096), 4096);
+        assert_eq!(round_up_to_page_size(4097, 4096), 8192);
+    }
+}

crates/runtime/src/sig_registry.rs

@@ -0,0 +1,44 @@
+//! Implement a registry of function signatures, for fast indirect call
+//! signature checking.
+
+use crate::vmcontext::VMSharedSignatureIndex;
+use crate::{hash_map, HashMap};
+use core::convert::TryFrom;
+use cranelift_codegen::ir;
+
+/// WebAssembly requires that the caller and callee signatures in an indirect
+/// call must match. To implement this efficiently, keep a registry of all
+/// signatures, shared by all instances, so that call sites can just do an
+/// index comparison.
+#[derive(Debug)]
+pub struct SignatureRegistry {
+    signature_hash: HashMap<ir::Signature, VMSharedSignatureIndex>,
+}
+
+impl SignatureRegistry {
+    /// Create a new `SignatureRegistry`.
+    pub fn new() -> Self {
+        Self {
+            signature_hash: HashMap::new(),
+        }
+    }
+
+    /// Register a signature and return its unique index.
+    pub fn register(&mut self, sig: &ir::Signature) -> VMSharedSignatureIndex {
+        let len = self.signature_hash.len();
+        match self.signature_hash.entry(sig.clone()) {
+            hash_map::Entry::Occupied(entry) => *entry.get(),
+            hash_map::Entry::Vacant(entry) => {
+                // Keep `signature_hash` len under 2**32 -- VMSharedSignatureIndex::new(core::u32::MAX)
+                // is reserved for VMSharedSignatureIndex::default().
+                debug_assert!(
+                    len < core::u32::MAX as usize,
+                    "Invariant check: signature_hash.len() < core::u32::MAX"
+                );
+                let sig_id = VMSharedSignatureIndex::new(u32::try_from(len).unwrap());
+                entry.insert(sig_id);
+                sig_id
+            }
+        }
+    }
+}

crates/runtime/src/signalhandlers.rs

@@ -0,0 +1,130 @@
+//! Interface to low-level signal-handling mechanisms.
+
+#![allow(non_upper_case_globals)]
+#![allow(non_camel_case_types)]
+#![allow(non_snake_case)]
+
+use crate::vmcontext::VMContext;
+use crate::RwLock;
+use core::borrow::{Borrow, BorrowMut};
+use core::cell::Cell;
+
+#[derive(Default)]
+struct TrapContext {
+    tried_to_install_signal_handlers: Cell<bool>,
+    have_signal_handlers: Cell<bool>,
+}
+
+extern "C" {
+    fn EnsureEagerSignalHandlers() -> libc::c_int;
+    #[cfg(any(target_os = "macos", target_os = "ios"))]
+    fn EnsureDarwinMachPorts() -> libc::c_int;
+}
+
+struct InstallState {
+    tried: bool,
+    success: bool,
+}
+
+impl InstallState {
+    fn new() -> Self {
+        Self {
+            tried: false,
+            success: false,
+        }
+    }
+}
+
+lazy_static! {
+    static ref EAGER_INSTALL_STATE: RwLock<InstallState> = RwLock::new(InstallState::new());
+    static ref LAZY_INSTALL_STATE: RwLock<InstallState> = RwLock::new(InstallState::new());
+}
+
+/// This function performs the low-overhead signal handler initialization that we
+/// want to do eagerly to ensure a more-deterministic global process state. This
+/// is especially relevant for signal handlers since handler ordering depends on
+/// installation order: the wasm signal handler must run *before* the other crash
+/// handlers and since POSIX signal handlers work LIFO, this function needs to be
+/// called at the end of the startup process, after other handlers have been
+/// installed. This function can thus be called multiple times, having no effect
+/// after the first call.
+#[no_mangle]
+pub extern "C" fn wasmtime_init_eager() {
+    let mut locked = EAGER_INSTALL_STATE.write().unwrap();
+    let state = locked.borrow_mut();
+
+    if state.tried {
+        return;
+    }
+
+    state.tried = true;
+    assert!(!state.success);
+
+    if unsafe { EnsureEagerSignalHandlers() == 0 } {
+        return;
+    }
+
+    state.success = true;
+}
+
+thread_local! {
+    static TRAP_CONTEXT: TrapContext = TrapContext::default();
+}
+
+/// Assuming `EnsureEagerProcessSignalHandlers` has already been called,
+/// this function performs the full installation of signal handlers which must
+/// be performed per-thread. This operation may incur some overhead and
+/// so should be done only when needed to use wasm.
+#[no_mangle]
+pub extern "C" fn wasmtime_init_finish(vmctx: &mut VMContext) {
+    if !TRAP_CONTEXT.with(|cx| cx.tried_to_install_signal_handlers.get()) {
+        TRAP_CONTEXT.with(|cx| {
+            cx.tried_to_install_signal_handlers.set(true);
+            assert!(!cx.have_signal_handlers.get());
+        });
+
+        {
+            let locked = EAGER_INSTALL_STATE.read().unwrap();
+            let state = locked.borrow();
+            assert!(
+                state.tried,
+                "call wasmtime_init_eager before calling wasmtime_init_finish"
+            );
+            if !state.success {
+                return;
+            }
+        }
+
+        #[cfg(any(target_os = "macos", target_os = "ios"))]
+        ensure_darwin_mach_ports();
+
+        TRAP_CONTEXT.with(|cx| {
+            cx.have_signal_handlers.set(true);
+        })
+    }
+
+    let instance = unsafe { vmctx.instance() };
+    let have_signal_handlers = TRAP_CONTEXT.with(|cx| cx.have_signal_handlers.get());
+    if !have_signal_handlers && instance.needs_signal_handlers() {
+        panic!("failed to install signal handlers");
+    }
+}
+
+#[cfg(any(target_os = "macos", target_os = "ios"))]
+fn ensure_darwin_mach_ports() {
+    let mut locked = LAZY_INSTALL_STATE.write().unwrap();
+    let state = locked.borrow_mut();
+
+    if state.tried {
+        return;
+    }
+
+    state.tried = true;
+    assert!(!state.success);
+
+    if unsafe { EnsureDarwinMachPorts() != 0 } {
+        return;
+    }
+
+    state.success = true;
+}

crates/runtime/src/table.rs

@@ -0,0 +1,101 @@
+//! Memory management for tables.
+//!
+//! `Table` is to WebAssembly tables what `LinearMemory` is to WebAssembly linear memories.
+
+use crate::vmcontext::{VMCallerCheckedAnyfunc, VMTableDefinition};
+use alloc::vec::Vec;
+use core::convert::{TryFrom, TryInto};
+use cranelift_wasm::TableElementType;
+use wasmtime_environ::{TablePlan, TableStyle};
+
+/// A table instance.
+#[derive(Debug)]
+pub struct Table {
+    vec: Vec<VMCallerCheckedAnyfunc>,
+    maximum: Option<u32>,
+}
+
+impl Table {
+    /// Create a new table instance with specified minimum and maximum number of elements.
+    pub fn new(plan: &TablePlan) -> Self {
+        match plan.table.ty {
+            TableElementType::Func => (),
+            TableElementType::Val(ty) => {
+                unimplemented!("tables of types other than anyfunc ({})", ty)
+            }
+        };
+        match plan.style {
+            TableStyle::CallerChecksSignature => Self {
+                vec: vec![
+                    VMCallerCheckedAnyfunc::default();
+                    usize::try_from(plan.table.minimum).unwrap()
+                ],
+                maximum: plan.table.maximum,
+            },
+        }
+    }
+
+    /// Returns the number of allocated elements.
+    pub fn size(&self) -> u32 {
+        self.vec.len().try_into().unwrap()
+    }
+
+    /// Grow table by the specified amount of elements.
+    ///
+    /// Returns `None` if table can't be grown by the specified amount
+    /// of elements.
+    pub fn grow(&mut self, delta: u32) -> Option<u32> {
+        let new_len = match self.size().checked_add(delta) {
+            Some(len) => {
+                if let Some(max) = self.maximum {
+                    if len > max {
+                        return None;
+                    }
+                }
+                len
+            }
+            None => {
+                return None;
+            }
+        };
+        self.vec.resize(
+            usize::try_from(new_len).unwrap(),
+            VMCallerCheckedAnyfunc::default(),
+        );
+        Some(new_len)
+    }
+
+    /// Get reference to the specified element.
+    ///
+    /// Returns `None` if the index is out of bounds.
+    pub fn get(&self, index: u32) -> Option<&VMCallerCheckedAnyfunc> {
+        self.vec.get(index as usize)
+    }
+
+    /// Get mutable reference to the specified element.
+    ///
+    /// Returns `None` if the index is out of bounds.
+    pub fn get_mut(&mut self, index: u32) -> Option<&mut VMCallerCheckedAnyfunc> {
+        self.vec.get_mut(index as usize)
+    }
+
+    /// Return a `VMTableDefinition` for exposing the table to compiled wasm code.
+    pub fn vmtable(&mut self) -> VMTableDefinition {
+        VMTableDefinition {
+            base: self.vec.as_mut_ptr() as *mut u8,
+            current_elements: self.vec.len().try_into().unwrap(),
+        }
+    }
+}
+
+impl AsRef<[VMCallerCheckedAnyfunc]> for Table {
+    fn as_ref(&self) -> &[VMCallerCheckedAnyfunc] {
+        self.vec.as_slice()
+    }
+}
+
+impl AsMut<[VMCallerCheckedAnyfunc]> for Table {
+    fn as_mut(&mut self) -> &mut [VMCallerCheckedAnyfunc] {
+        self.vec.as_mut_slice()
+    }
+}

crates/runtime/src/trap_registry.rs

@@ -0,0 +1,71 @@
+use crate::HashMap;
+use crate::{RwLock, RwLockReadGuard, RwLockWriteGuard};
+use cranelift_codegen::ir;
+use lazy_static::lazy_static;
+
+lazy_static! {
+    static ref REGISTRY: RwLock<TrapRegistry> = RwLock::new(TrapRegistry::default());
+}
+
+/// The registry maintains descriptions of traps in currently allocated functions.
+#[derive(Default)]
+pub struct TrapRegistry {
+    traps: HashMap<usize, TrapDescription>,
+}
+
+/// Description of a trap.
+#[derive(Clone, Copy, PartialEq, Debug)]
+pub struct TrapDescription {
+    /// Location of the trap in source binary module.
+    pub source_loc: ir::SourceLoc,
+    /// Code of the trap.
+    pub trap_code: ir::TrapCode,
+}
+
+/// RAII guard for deregistering traps
+pub struct TrapRegistrationGuard(usize);
+
+impl TrapRegistry {
+    /// Registers a new trap.
+    /// Returns a RAII guard that deregisters the trap when dropped.
+    pub fn register_trap(
+        &mut self,
+        address: usize,
+        source_loc: ir::SourceLoc,
+        trap_code: ir::TrapCode,
+    ) -> TrapRegistrationGuard {
+        let entry = TrapDescription {
+            source_loc,
+            trap_code,
+        };
+        let previous_trap = self.traps.insert(address, entry);
+        assert!(previous_trap.is_none());
+        TrapRegistrationGuard(address)
+    }
+
+    fn deregister_trap(&mut self, address: usize) {
+        assert!(self.traps.remove(&address).is_some());
+    }
+
+    /// Gets a trap description at given address.
+    pub fn get_trap(&self, address: usize) -> Option<TrapDescription> {
+        self.traps.get(&address).copied()
+    }
+}
+
+impl Drop for TrapRegistrationGuard {
+    fn drop(&mut self) {
+        let mut registry = get_mut_trap_registry();
+        registry.deregister_trap(self.0);
+    }
+}
+
+/// Gets guarded writable reference to traps registry
+pub fn get_mut_trap_registry() -> RwLockWriteGuard<'static, TrapRegistry> {
+    REGISTRY.write().expect("trap registry lock got poisoned")
+}
+
+/// Gets guarded readable reference to traps registry
+pub fn get_trap_registry() -> RwLockReadGuard<'static, TrapRegistry> {
+    REGISTRY.read().expect("trap registry lock got poisoned")
+}

crates/runtime/src/traphandlers.rs

@@ -0,0 +1,170 @@
+//! WebAssembly trap handling, which is built on top of the lower-level
+//! signalhandling mechanisms.
+
+use crate::trap_registry::get_trap_registry;
+use crate::trap_registry::TrapDescription;
+use crate::vmcontext::{VMContext, VMFunctionBody};
+use alloc::string::{String, ToString};
+use core::cell::Cell;
+use core::ptr;
+use cranelift_codegen::ir;
+
+extern "C" {
+    fn WasmtimeCallTrampoline(
+        vmctx: *mut u8,
+        callee: *const VMFunctionBody,
+        values_vec: *mut u8,
+    ) -> i32;
+    fn WasmtimeCall(vmctx: *mut u8, callee: *const VMFunctionBody) -> i32;
+}
+
+thread_local! {
+    static RECORDED_TRAP: Cell<Option<TrapDescription>> = Cell::new(None);
+    static JMP_BUF: Cell<*const u8> = Cell::new(ptr::null());
+    static RESET_GUARD_PAGE: Cell<bool> = Cell::new(false);
+}
+
+/// Check if there is a trap at given PC
+#[doc(hidden)]
+#[allow(non_snake_case)]
+#[no_mangle]
+pub extern "C" fn CheckIfTrapAtAddress(_pc: *const u8) -> i8 {
+    // TODO: stack overflow can happen at any random time (i.e. in malloc() in memory.grow)
+    // and it's really hard to determine if the cause was stack overflow and if it happened
+    // in WebAssembly module.
+    // So, let's assume that any untrusted code called from WebAssembly doesn't trap.
+    // Then, if we have called some WebAssembly code, it means the trap is stack overflow.
+    JMP_BUF.with(|ptr| !ptr.get().is_null()) as i8
+}
+
+/// Record the Trap code and wasm bytecode offset in TLS somewhere
+#[doc(hidden)]
+#[allow(non_snake_case)]
+#[no_mangle]
+pub extern "C" fn RecordTrap(pc: *const u8, reset_guard_page: bool) {
+    // TODO: please see explanation in CheckIfTrapAtAddress.
+    let registry = get_trap_registry();
+    let trap_desc = registry
+        .get_trap(pc as usize)
+        .unwrap_or_else(|| TrapDescription {
+            source_loc: ir::SourceLoc::default(),
+            trap_code: ir::TrapCode::StackOverflow,
+        });
+
+    if reset_guard_page {
+        RESET_GUARD_PAGE.with(|v| v.set(true));
+    }
+
+    RECORDED_TRAP.with(|data| {
+        assert_eq!(
+            data.get(),
+            None,
+            "Only one trap per thread can be recorded at a moment!"
+        );
+        data.set(Some(trap_desc))
+    });
+}
+
+#[doc(hidden)]
+#[allow(non_snake_case)]
+#[no_mangle]
+pub extern "C" fn EnterScope(ptr: *const u8) -> *const u8 {
+    JMP_BUF.with(|buf| buf.replace(ptr))
+}
+
+#[doc(hidden)]
+#[allow(non_snake_case)]
+#[no_mangle]
+pub extern "C" fn GetScope() -> *const u8 {
+    JMP_BUF.with(|buf| buf.get())
+}
+
+#[doc(hidden)]
+#[allow(non_snake_case)]
+#[no_mangle]
+pub extern "C" fn LeaveScope(ptr: *const u8) {
+    RESET_GUARD_PAGE.with(|v| {
+        if v.get() {
+            reset_guard_page();
+            v.set(false);
+        }
+    });
+
+    JMP_BUF.with(|buf| buf.set(ptr))
+}
+
+#[cfg(target_os = "windows")]
+fn reset_guard_page() {
+    extern "C" {
+        fn _resetstkoflw() -> winapi::ctypes::c_int;
+    }
+
+    // We need to restore guard page under stack to handle future stack overflows properly.
+    // https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/resetstkoflw?view=vs-2019
+    if unsafe { _resetstkoflw() } == 0 {
+        panic!("failed to restore stack guard page");
+    }
+}
+
+#[cfg(not(target_os = "windows"))]
+fn reset_guard_page() {}
+
+fn trap_message() -> String {
+    let trap_desc = RECORDED_TRAP
+        .with(|data| data.replace(None))
+        .expect("trap_message must be called after trap occurred");
+
+    format!(
+        "wasm trap: {}, source location: {}",
+        trap_code_to_expected_string(trap_desc.trap_code),
+        trap_desc.source_loc,
+    )
+}
+
+fn trap_code_to_expected_string(trap_code: ir::TrapCode) -> String {
+    use ir::TrapCode::*;
+    match trap_code {
+        StackOverflow => "call stack exhausted".to_string(),
+        HeapOutOfBounds => "out of bounds memory access".to_string(),
+        TableOutOfBounds => "undefined element".to_string(),
+        OutOfBounds => "out of bounds".to_string(), // Note: not covered by the test suite
+        IndirectCallToNull => "uninitialized element".to_string(),
+        BadSignature => "indirect call type mismatch".to_string(),
+        IntegerOverflow => "integer overflow".to_string(),
+        IntegerDivisionByZero => "integer divide by zero".to_string(),
+        BadConversionToInteger => "invalid conversion to integer".to_string(),
+        UnreachableCodeReached => "unreachable".to_string(),
+        Interrupt => "interrupt".to_string(), // Note: not covered by the test suite
+        User(x) => format!("user trap {}", x), // Note: not covered by the test suite
+    }
+}
+
+/// Call the wasm function pointed to by `callee`. `values_vec` points to
+/// a buffer which holds the incoming arguments, and to which the outgoing
+/// return values will be written.
+#[no_mangle]
+pub unsafe extern "C" fn wasmtime_call_trampoline(
+    vmctx: *mut VMContext,
+    callee: *const VMFunctionBody,
+    values_vec: *mut u8,
+) -> Result<(), String> {
+    if WasmtimeCallTrampoline(vmctx as *mut u8, callee, values_vec) == 0 {
+        Err(trap_message())
+    } else {
+        Ok(())
+    }
+}
+
+/// Call the wasm function pointed to by `callee`, which has no arguments or
+/// return values.
+#[no_mangle]
+pub unsafe extern "C" fn wasmtime_call(
+    vmctx: *mut VMContext,
+    callee: *const VMFunctionBody,
+) -> Result<(), String> {
+    if WasmtimeCall(vmctx as *mut u8, callee) == 0 {
+        Err(trap_message())
+    } else {
+        Ok(())
+    }
+}

crates/runtime/src/vmcontext.rs

@@ -0,0 +1,615 @@
+//! This file declares `VMContext` and several related structs which contain
+//! fields that compiled wasm code accesses directly.
+
+use crate::instance::Instance;
+use core::any::Any;
+use core::{ptr, u32};
+use wasmtime_environ::BuiltinFunctionIndex;
+
+/// An imported function.
+#[derive(Debug, Copy, Clone)]
+#[repr(C)]
+pub struct VMFunctionImport {
+    /// A pointer to the imported function body.
+    pub body: *const VMFunctionBody,
+
+    /// A pointer to the `VMContext` that owns the function.
+    pub vmctx: *mut VMContext,
+}
+
+#[cfg(test)]
+mod test_vmfunction_import {
+    use super::VMFunctionImport;
+    use core::mem::size_of;
+    use wasmtime_environ::{Module, VMOffsets};
+
+    #[test]
+    fn check_vmfunction_import_offsets() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMFunctionImport>(),
+            usize::from(offsets.size_of_vmfunction_import())
+        );
+        assert_eq!(
+            offset_of!(VMFunctionImport, body),
+            usize::from(offsets.vmfunction_import_body())
+        );
+        assert_eq!(
+            offset_of!(VMFunctionImport, vmctx),
+            usize::from(offsets.vmfunction_import_vmctx())
+        );
+    }
+}
+
+/// A placeholder byte-sized type which is just used to provide some amount of type
+/// safety when dealing with pointers to JIT-compiled function bodies. Note that it's
+/// deliberately not Copy, as we shouldn't be carelessly copying function body bytes
+/// around.
+#[repr(C)]
+pub struct VMFunctionBody(u8);
+
+#[cfg(test)]
+mod test_vmfunction_body {
+    use super::VMFunctionBody;
+    use core::mem::size_of;
+
+    #[test]
+    fn check_vmfunction_body_offsets() {
+        assert_eq!(size_of::<VMFunctionBody>(), 1);
+    }
+}
+
+/// The fields compiled code needs to access to utilize a WebAssembly table
+/// imported from another instance.
+#[derive(Debug, Copy, Clone)]
+#[repr(C)]
+pub struct VMTableImport {
+    /// A pointer to the imported table description.
+    pub from: *mut VMTableDefinition,
+
+    /// A pointer to the `VMContext` that owns the table description.
+    pub vmctx: *mut VMContext,
+}
+
+#[cfg(test)]
+mod test_vmtable_import {
+    use super::VMTableImport;
+    use core::mem::size_of;
+    use wasmtime_environ::{Module, VMOffsets};
+
+    #[test]
+    fn check_vmtable_import_offsets() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMTableImport>(),
+            usize::from(offsets.size_of_vmtable_import())
+        );
+        assert_eq!(
+            offset_of!(VMTableImport, from),
+            usize::from(offsets.vmtable_import_from())
+        );
+        assert_eq!(
+            offset_of!(VMTableImport, vmctx),
+            usize::from(offsets.vmtable_import_vmctx())
+        );
+    }
+}
+
+/// The fields compiled code needs to access to utilize a WebAssembly linear
+/// memory imported from another instance.
+#[derive(Debug, Copy, Clone)]
+#[repr(C)]
+pub struct VMMemoryImport {
+    /// A pointer to the imported memory description.
+    pub from: *mut VMMemoryDefinition,
+
+    /// A pointer to the `VMContext` that owns the memory description.
+    pub vmctx: *mut VMContext,
+}
+
+#[cfg(test)]
+mod test_vmmemory_import {
+    use super::VMMemoryImport;
+    use core::mem::size_of;
+    use wasmtime_environ::{Module, VMOffsets};
+
+    #[test]
+    fn check_vmmemory_import_offsets() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMMemoryImport>(),
+            usize::from(offsets.size_of_vmmemory_import())
+        );
+        assert_eq!(
+            offset_of!(VMMemoryImport, from),
+            usize::from(offsets.vmmemory_import_from())
+        );
+        assert_eq!(
+            offset_of!(VMMemoryImport, vmctx),
+            usize::from(offsets.vmmemory_import_vmctx())
+        );
+    }
+}
+
+/// The fields compiled code needs to access to utilize a WebAssembly global
+/// variable imported from another instance.
+#[derive(Debug, Copy, Clone)]
+#[repr(C)]
+pub struct VMGlobalImport {
+    /// A pointer to the imported global variable description.
+    pub from: *mut VMGlobalDefinition,
+}
+
+#[cfg(test)]
+mod test_vmglobal_import {
+    use super::VMGlobalImport;
+    use core::mem::size_of;
+    use wasmtime_environ::{Module, VMOffsets};
+
+    #[test]
+    fn check_vmglobal_import_offsets() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMGlobalImport>(),
+            usize::from(offsets.size_of_vmglobal_import())
+        );
+        assert_eq!(
+            offset_of!(VMGlobalImport, from),
+            usize::from(offsets.vmglobal_import_from())
+        );
+    }
+}
+
+/// The fields compiled code needs to access to utilize a WebAssembly linear
+/// memory defined within the instance, namely the start address and the
+/// size in bytes.
+#[derive(Debug, Copy, Clone)]
+#[repr(C)]
+pub struct VMMemoryDefinition {
+    /// The start address.
+    pub base: *mut u8,
+
+    /// The current logical size of this linear memory in bytes.
+    pub current_length: usize,
+}
+
+#[cfg(test)]
+mod test_vmmemory_definition {
+    use super::VMMemoryDefinition;
+    use core::mem::size_of;
+    use wasmtime_environ::{Module, VMOffsets};
+
+    #[test]
+    fn check_vmmemory_definition_offsets() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMMemoryDefinition>(),
+            usize::from(offsets.size_of_vmmemory_definition())
+        );
+        assert_eq!(
+            offset_of!(VMMemoryDefinition, base),
+            usize::from(offsets.vmmemory_definition_base())
+        );
+        assert_eq!(
+            offset_of!(VMMemoryDefinition, current_length),
+            usize::from(offsets.vmmemory_definition_current_length())
+        );
+        /* TODO: Assert that the size of `current_length` matches.
+        assert_eq!(
+            size_of::<VMMemoryDefinition::current_length>(),
+            usize::from(offsets.size_of_vmmemory_definition_current_length())
+        );
+        */
+    }
+}
+
+/// The fields compiled code needs to access to utilize a WebAssembly table
+/// defined within the instance.
+#[derive(Debug, Copy, Clone)]
+#[repr(C)]
+pub struct VMTableDefinition {
+    /// Pointer to the table data.
+    pub base: *mut u8,
+
+    /// The current number of elements in the table.
+    pub current_elements: u32,
+}
+
+#[cfg(test)]
+mod test_vmtable_definition {
+    use super::VMTableDefinition;
+    use core::mem::size_of;
+    use wasmtime_environ::{Module, VMOffsets};
+
+    #[test]
+    fn check_vmtable_definition_offsets() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMTableDefinition>(),
+            usize::from(offsets.size_of_vmtable_definition())
+        );
+        assert_eq!(
+            offset_of!(VMTableDefinition, base),
+            usize::from(offsets.vmtable_definition_base())
+        );
+        assert_eq!(
+            offset_of!(VMTableDefinition, current_elements),
+            usize::from(offsets.vmtable_definition_current_elements())
+        );
+    }
+}
+
+/// The storage for a WebAssembly global defined within the instance.
+///
+/// TODO: Pack the globals more densely, rather than using the same size
+/// for every type.
+#[derive(Debug, Copy, Clone)]
+#[repr(C, align(16))]
+pub struct VMGlobalDefinition {
+    storage: [u8; 16],
+    // If more elements are added here, remember to add offset_of tests below!
+}
+
+#[cfg(test)]
+mod test_vmglobal_definition {
+    use super::VMGlobalDefinition;
+    use core::mem::{align_of, size_of};
+    use wasmtime_environ::{Module, VMOffsets};
+
+    #[test]
+    fn check_vmglobal_definition_alignment() {
+        assert!(align_of::<VMGlobalDefinition>() >= align_of::<i32>());
+        assert!(align_of::<VMGlobalDefinition>() >= align_of::<i64>());
+        assert!(align_of::<VMGlobalDefinition>() >= align_of::<f32>());
+        assert!(align_of::<VMGlobalDefinition>() >= align_of::<f64>());
+        assert!(align_of::<VMGlobalDefinition>() >= align_of::<[u8; 16]>());
+    }
+
+    #[test]
+    fn check_vmglobal_definition_offsets() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMGlobalDefinition>(),
+            usize::from(offsets.size_of_vmglobal_definition())
+        );
+    }
+
+    #[test]
+    fn check_vmglobal_begins_aligned() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(offsets.vmctx_globals_begin() % 16, 0);
+    }
+}
+
+impl VMGlobalDefinition {
+    /// Construct a `VMGlobalDefinition`.
+    pub fn new() -> Self {
+        Self { storage: [0; 16] }
+    }
+
+    /// Return a reference to the value as an i32.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_i32(&self) -> &i32 {
+        &*(self.storage.as_ref().as_ptr() as *const i32)
+    }
+
+    /// Return a mutable reference to the value as an i32.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_i32_mut(&mut self) -> &mut i32 {
+        &mut *(self.storage.as_mut().as_mut_ptr() as *mut i32)
+    }
+
+    /// Return a reference to the value as a u32.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_u32(&self) -> &u32 {
+        &*(self.storage.as_ref().as_ptr() as *const u32)
+    }
+
+    /// Return a mutable reference to the value as an u32.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_u32_mut(&mut self) -> &mut u32 {
+        &mut *(self.storage.as_mut().as_mut_ptr() as *mut u32)
+    }
+
+    /// Return a reference to the value as an i64.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_i64(&self) -> &i64 {
+        &*(self.storage.as_ref().as_ptr() as *const i64)
+    }
+
+    /// Return a mutable reference to the value as an i64.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_i64_mut(&mut self) -> &mut i64 {
+        &mut *(self.storage.as_mut().as_mut_ptr() as *mut i64)
+    }
+
+    /// Return a reference to the value as an u64.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_u64(&self) -> &u64 {
+        &*(self.storage.as_ref().as_ptr() as *const u64)
+    }
+
+    /// Return a mutable reference to the value as an u64.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_u64_mut(&mut self) -> &mut u64 {
+        &mut *(self.storage.as_mut().as_mut_ptr() as *mut u64)
+    }
+
+    /// Return a reference to the value as an f32.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_f32(&self) -> &f32 {
+        &*(self.storage.as_ref().as_ptr() as *const f32)
+    }
+
+    /// Return a mutable reference to the value as an f32.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_f32_mut(&mut self) -> &mut f32 {
+        &mut *(self.storage.as_mut().as_mut_ptr() as *mut f32)
+    }
+
+    /// Return a reference to the value as f32 bits.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_f32_bits(&self) -> &u32 {
+        &*(self.storage.as_ref().as_ptr() as *const u32)
+    }
+
+    /// Return a mutable reference to the value as f32 bits.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_f32_bits_mut(&mut self) -> &mut u32 {
+        &mut *(self.storage.as_mut().as_mut_ptr() as *mut u32)
+    }
+
+    /// Return a reference to the value as an f64.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_f64(&self) -> &f64 {
+        &*(self.storage.as_ref().as_ptr() as *const f64)
+    }
+
+    /// Return a mutable reference to the value as an f64.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_f64_mut(&mut self) -> &mut f64 {
+        &mut *(self.storage.as_mut().as_mut_ptr() as *mut f64)
+    }
+
+    /// Return a reference to the value as f64 bits.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_f64_bits(&self) -> &u64 {
+        &*(self.storage.as_ref().as_ptr() as *const u64)
+    }
+
+    /// Return a mutable reference to the value as f64 bits.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_f64_bits_mut(&mut self) -> &mut u64 {
+        &mut *(self.storage.as_mut().as_mut_ptr() as *mut u64)
+    }
+
+    /// Return a reference to the value as an u128.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_u128(&self) -> &u128 {
+        &*(self.storage.as_ref().as_ptr() as *const u128)
+    }
+
+    /// Return a mutable reference to the value as an u128.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_u128_mut(&mut self) -> &mut u128 {
+        &mut *(self.storage.as_mut().as_mut_ptr() as *mut u128)
+    }
+
+    /// Return a reference to the value as u128 bits.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_u128_bits(&self) -> &[u8; 16] {
+        &*(self.storage.as_ref().as_ptr() as *const [u8; 16])
+    }
+
+    /// Return a mutable reference to the value as u128 bits.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub unsafe fn as_u128_bits_mut(&mut self) -> &mut [u8; 16] {
+        &mut *(self.storage.as_mut().as_mut_ptr() as *mut [u8; 16])
+    }
+}
+
+/// An index into the shared signature registry, usable for checking signatures
+/// at indirect calls.
+#[repr(C)]
+#[derive(Debug, Eq, PartialEq, Clone, Copy, Hash)]
+pub struct VMSharedSignatureIndex(u32);
+
+#[cfg(test)]
+mod test_vmshared_signature_index {
+    use super::VMSharedSignatureIndex;
+    use core::mem::size_of;
+    use wasmtime_environ::{Module, TargetSharedSignatureIndex, VMOffsets};
+
+    #[test]
+    fn check_vmshared_signature_index() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMSharedSignatureIndex>(),
+            usize::from(offsets.size_of_vmshared_signature_index())
+        );
+    }
+
+    #[test]
+    fn check_target_shared_signature_index() {
+        assert_eq!(
+            size_of::<VMSharedSignatureIndex>(),
+            size_of::<TargetSharedSignatureIndex>()
+        );
+    }
+}
+
+impl VMSharedSignatureIndex {
+    /// Create a new `VMSharedSignatureIndex`.
+    pub fn new(value: u32) -> Self {
+        Self(value)
+    }
+}
+
+impl Default for VMSharedSignatureIndex {
+    fn default() -> Self {
+        Self::new(u32::MAX)
+    }
+}
+
+/// The VM caller-checked "anyfunc" record, for caller-side signature checking.
+/// It consists of the actual function pointer and a signature id to be checked
+/// by the caller.
+#[derive(Debug, Clone)]
+#[repr(C)]
+pub struct VMCallerCheckedAnyfunc {
+    /// Function body.
+    pub func_ptr: *const VMFunctionBody,
+    /// Function signature id.
+    pub type_index: VMSharedSignatureIndex,
+    /// Function `VMContext`.
+    pub vmctx: *mut VMContext,
+    // If more elements are added here, remember to add offset_of tests below!
+}
+
+#[cfg(test)]
+mod test_vmcaller_checked_anyfunc {
+    use super::VMCallerCheckedAnyfunc;
+    use core::mem::size_of;
+    use wasmtime_environ::{Module, VMOffsets};
+
+    #[test]
+    fn check_vmcaller_checked_anyfunc_offsets() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMCallerCheckedAnyfunc>(),
+            usize::from(offsets.size_of_vmcaller_checked_anyfunc())
+        );
+        assert_eq!(
+            offset_of!(VMCallerCheckedAnyfunc, func_ptr),
+            usize::from(offsets.vmcaller_checked_anyfunc_func_ptr())
+        );
+        assert_eq!(
+            offset_of!(VMCallerCheckedAnyfunc, type_index),
+            usize::from(offsets.vmcaller_checked_anyfunc_type_index())
+        );
+        assert_eq!(
+            offset_of!(VMCallerCheckedAnyfunc, vmctx),
+            usize::from(offsets.vmcaller_checked_anyfunc_vmctx())
+        );
+    }
+}
+
+impl Default for VMCallerCheckedAnyfunc {
+    fn default() -> Self {
+        Self {
+            func_ptr: ptr::null_mut(),
+            type_index: Default::default(),
+            vmctx: ptr::null_mut(),
+        }
+    }
+}
+
+/// An array that stores addresses of builtin functions. We translate code
+/// to use indirect calls. This way, we don't have to patch the code.
+#[repr(C)]
+pub struct VMBuiltinFunctionsArray {
+    ptrs: [usize; Self::len()],
+}
+
+impl VMBuiltinFunctionsArray {
+    pub const fn len() -> usize {
+        BuiltinFunctionIndex::builtin_functions_total_number() as usize
+    }
+
+    pub fn initialized() -> Self {
+        use crate::libcalls::*;
+        let mut ptrs = [0; Self::len()];
+        ptrs[BuiltinFunctionIndex::get_memory32_grow_index().index() as usize] =
+            wasmtime_memory32_grow as usize;
+        ptrs[BuiltinFunctionIndex::get_imported_memory32_grow_index().index() as usize] =
+            wasmtime_imported_memory32_grow as usize;
+        ptrs[BuiltinFunctionIndex::get_memory32_size_index().index() as usize] =
+            wasmtime_memory32_size as usize;
+        ptrs[BuiltinFunctionIndex::get_imported_memory32_size_index().index() as usize] =
+            wasmtime_imported_memory32_size as usize;
+        Self { ptrs }
+    }
+}
+
+/// The storage for a WebAssembly invocation argument
+///
+/// TODO: These could be packed more densely, rather than using the same size for every type.
+#[derive(Debug, Copy, Clone)]
+#[repr(C, align(16))]
+pub struct VMInvokeArgument([u8; 16]);
+
+#[cfg(test)]
+mod test_vm_invoke_argument {
+    use super::VMInvokeArgument;
+    use core::mem::{align_of, size_of};
+    use wasmtime_environ::{Module, VMOffsets};
+
+    #[test]
+    fn check_vm_invoke_argument_alignment() {
+        assert_eq!(align_of::<VMInvokeArgument>(), 16);
+    }
+
+    #[test]
+    fn check_vmglobal_definition_offsets() {
+        let module = Module::new();
+        let offsets = VMOffsets::new(size_of::<*mut u8>() as u8, &module);
+        assert_eq!(
+            size_of::<VMInvokeArgument>(),
+            usize::from(offsets.size_of_vmglobal_definition())
+        );
+    }
+}
+
+impl VMInvokeArgument {
+    /// Create a new invocation argument filled with zeroes
+    pub fn new() -> Self {
+        Self([0; 16])
+    }
+}
+
+/// The VM "context", which is pointed to by the `vmctx` arg in Cranelift.
+/// This has information about globals, memories, tables, and other runtime
+/// state associated with the current instance.
+///
+/// The struct here is empty, as the sizes of these fields are dynamic, and
+/// we can't describe them in Rust's type system. Sufficient memory is
+/// allocated at runtime.
+///
+/// TODO: We could move the globals into the `vmctx` allocation too.
+#[derive(Debug)]
+#[repr(C)]
+pub struct VMContext {}
+
+impl VMContext {
+    /// Return a mutable reference to the associated `Instance`.
+    ///
+    /// This is unsafe because it doesn't work on just any `VMContext`, it must
+    /// be a `VMContext` allocated as part of an `Instance`.
+    #[allow(clippy::cast_ptr_alignment)]
+    pub(crate) unsafe fn instance(&mut self) -> &mut Instance {
+        &mut *((self as *mut Self as *mut u8).offset(-Instance::vmctx_offset()) as *mut Instance)
+    }
+
+    /// Return a mutable reference to the host state associated with this `Instance`.
+    ///
+    /// This is unsafe because it doesn't work on just any `VMContext`, it must
+    /// be a `VMContext` allocated as part of an `Instance`.
+    pub unsafe fn host_state(&mut self) -> &mut dyn Any {
+        self.instance().host_state()
+    }
+
+    /// Lookup an export in the global exports namespace.
+    pub unsafe fn lookup_global_export(&mut self, field: &str) -> Option<crate::export::Export> {
+        self.instance().lookup_global_export(field)
+    }
+}