Connect helper C symbols to their static library

This commit adds a `#[link]` annotation to the block defining symbols
coming from a native static library that we build and link. This is
required by rustc to get symbols to get exported correctly when linking
wasmtime into a Rust dynamic library instead of always as an rlib.

While I was at it I went ahead and renamed the symbols now that they're
no longer in C++ and they're doing setjmp/longjmp and not much else.

Closes #3006

crates/runtime/src/helpers.c

@@ -14,7 +14,7 @@
 #define platform_jmp_buf sigjmp_buf
 #endif
 
-int RegisterSetjmp(
+int wasmtime_setjmp(
     void **buf_storage,
     void (*body)(void*, void*),
     void *payload,
@@ -28,7 +28,7 @@ int RegisterSetjmp(
   return 1;
 }
 
-void Unwind(void *JmpBuf) {
+void wasmtime_longjmp(void *JmpBuf) {
   platform_jmp_buf *buf = (platform_jmp_buf*) JmpBuf;
   platform_longjmp(*buf, 1);
 }

crates/runtime/src/traphandlers.rs

@@ -14,15 +14,16 @@ use wasmtime_environ::ir;
 
 pub use self::tls::{tls_eager_initialize, TlsRestore};
 
+#[link(name = "wasmtime-helpers")]
 extern "C" {
     #[allow(improper_ctypes)]
-    fn RegisterSetjmp(
+    fn wasmtime_setjmp(
         jmp_buf: *mut *const u8,
         callback: extern "C" fn(*mut u8, *mut VMContext),
         payload: *mut u8,
         callee: *mut VMContext,
     ) -> i32;
-    fn Unwind(jmp_buf: *const u8) -> !;
+    fn wasmtime_longjmp(jmp_buf: *const u8) -> !;
 }
 
 cfg_if::cfg_if! {
@@ -177,7 +178,7 @@ where
     F: FnMut(*mut VMContext),
 {
     return CallThreadState::new(signal_handler).with(vminterrupts, |cx| {
-        RegisterSetjmp(
+        wasmtime_setjmp(
             cx.jmp_buf.as_ptr(),
             call_closure::<F>,
             &mut closure as *mut F as *mut u8,
@@ -251,7 +252,7 @@ impl CallThreadState {
     fn unwind_with(&self, reason: UnwindReason) -> ! {
         unsafe {
             (*self.unwind.get()).as_mut_ptr().write(reason);
-            Unwind(self.jmp_buf.get());
+            wasmtime_longjmp(self.jmp_buf.get());
         }
     }
 
@@ -306,7 +307,7 @@ impl CallThreadState {
         }
 
         // If all that passed then this is indeed a wasm trap, so return the
-        // `jmp_buf` passed to `Unwind` to resume.
+        // `jmp_buf` passed to `wasmtime_longjmp` to resume.
         self.jmp_buf.get()
     }
 

crates/runtime/src/traphandlers/macos.rs

@@ -33,7 +33,7 @@
 
 #![allow(non_snake_case)]
 
-use crate::traphandlers::{tls, Trap, Unwind};
+use crate::traphandlers::{tls, wasmtime_longjmp, Trap};
 use mach::exception_types::*;
 use mach::kern_return::*;
 use mach::mach_init::*;
@@ -389,7 +389,7 @@ unsafe extern "C" fn unwind(wasm_pc: *const u8) -> ! {
         state.jmp_buf.get()
     });
     debug_assert!(!jmp_buf.is_null());
-    Unwind(jmp_buf);
+    wasmtime_longjmp(jmp_buf);
 }
 
 thread_local! {

crates/runtime/src/traphandlers/unix.rs

@@ -1,4 +1,4 @@
-use crate::traphandlers::{tls, Trap, Unwind};
+use crate::traphandlers::{tls, wasmtime_longjmp, Trap};
 use std::cell::RefCell;
 use std::convert::TryInto;
 use std::io;
@@ -99,7 +99,7 @@ unsafe extern "C" fn trap_handler(
             return true;
         }
         info.capture_backtrace(pc);
-        Unwind(jmp_buf)
+        wasmtime_longjmp(jmp_buf)
     });
 
     if handled {

crates/runtime/src/traphandlers/windows.rs

@@ -1,4 +1,4 @@
-use crate::traphandlers::{tls, Trap, Unwind};
+use crate::traphandlers::{tls, wasmtime_longjmp, Trap};
 use std::io;
 use winapi::um::errhandlingapi::*;
 use winapi::um::minwinbase::*;
@@ -69,7 +69,7 @@ unsafe extern "system" fn exception_handler(exception_info: PEXCEPTION_POINTERS)
             EXCEPTION_CONTINUE_EXECUTION
         } else {
             info.capture_backtrace(ip);
-            Unwind(jmp_buf)
+            wasmtime_longjmp(jmp_buf)
         }
     })
 }