Split global_asm! helper macros out from wasmtime-fibers (#4454)

This moves them into a new `wasmtime-asm-macros` crate that can be used not just
from the `wasmtime-fibers` crate but also from other crates (e.g. we will need
them in https://github.com/bytecodealliance/wasmtime/pull/4431).

crates/fiber/Cargo.toml

@@ -18,6 +18,7 @@ cfg-if = "1.0"
 
 [target.'cfg(unix)'.dependencies]
 rustix = { version = "0.35.6", features = ["mm", "param"] }
+wasmtime-asm-macros = { version = "=0.40.0", path = "../asm-macros" }
 
 [target.'cfg(windows)'.dependencies.windows-sys]
 version = "0.36.1"

crates/fiber/src/unix.rs

@@ -177,63 +177,6 @@ impl Suspend {
     }
 }
 
-// This macro itself generates a macro named `asm_func!` which is suitable for
-// generating a single `global_asm!`-defined function. This takes care of
-// platform-specific directives to get the symbol attributes correct (e.g. ELF
-// symbols get a size and are flagged as a function) and additionally handles
-// visibility across platforms. All symbols should be visible to Rust but not
-// visible externally outside of a `*.so`.
-cfg_if::cfg_if! {
-    if #[cfg(target_os = "macos")] {
-        macro_rules! asm_func {
-            ($name:tt, $($body:tt)*) => {
-                std::arch::global_asm!(concat!(
-                    ".p2align 4\n",
-                    ".private_extern _", $name, "\n",
-                    ".global _", $name, "\n",
-                    "_", $name, ":\n",
-                    $($body)*
-                ));
-            };
-        }
-        macro_rules! asm_sym {
-            ($name:tt) => (concat!("_", $name))
-        }
-    } else {
-        // Note that for now this "else" clause just assumes that everything
-        // other than macOS is ELF and has the various directives here for
-        // that.
-        cfg_if::cfg_if! {
-            if #[cfg(target_arch = "arm")] {
-                macro_rules! elf_func_type_header {
-                    ($name:tt) => (concat!(".type ", $name, ",%function\n"))
-                }
-            } else {
-                macro_rules! elf_func_type_header {
-                    ($name:tt) => (concat!(".type ", $name, ",@function\n"))
-                }
-            }
-        }
-
-        macro_rules! asm_func {
-            ($name:tt, $($body:tt)*) => {
-                std::arch::global_asm!(concat!(
-                    ".p2align 4\n",
-                    ".hidden ", $name, "\n",
-                    ".global ", $name, "\n",
-                    elf_func_type_header!($name),
-                    $name, ":\n",
-                    $($body)*
-                    ".size ", $name, ",.-", $name,
-                ));
-            };
-        }
-        macro_rules! asm_sym {
-            ($name:tt) => ($name)
-        }
-    }
-}
-
 cfg_if::cfg_if! {
     if #[cfg(target_arch = "aarch64")] {
         mod aarch64;

crates/fiber/src/unix/aarch64.rs

@@ -18,6 +18,8 @@
 //   `DW_CFA_AARCH64_negate_ra_state` DWARF operation (aliased with the
 //   `.cfi_window_save` assembler directive) informs an unwinder about this
 
+use wasmtime_asm_macros::asm_func;
+
 cfg_if::cfg_if! {
     if #[cfg(target_os = "macos")] {
         macro_rules! cfi_window_save { () => (""); }

crates/fiber/src/unix/arm.rs

@@ -8,6 +8,8 @@
 // Also at this time this file is heavily based off the x86_64 file, so you'll
 // probably want to read that one as well.
 
+use wasmtime_asm_macros::{asm_func, asm_sym};
+
 // fn(top_of_stack(%r0): *mut u8)
 asm_func!(
     "wasmtime_fiber_switch",

crates/fiber/src/unix/x86.rs

@@ -10,6 +10,8 @@
 // different so the reserved space at the top of the stack is 8 bytes, not 16
 // bytes. Still two pointers though.
 
+use wasmtime_asm_macros::{asm_func, asm_sym};
+
 // fn(top_of_stack: *mut u8)
 asm_func!(
     "wasmtime_fiber_switch",

crates/fiber/src/unix/x86_64.rs

@@ -5,6 +5,8 @@
 // all the other bits. Documentation tries to reference various bits here and
 // there but try to make sure to read over everything before tweaking things!
 
+use wasmtime_asm_macros::{asm_func, asm_sym};
+
 // fn(top_of_stack(rdi): *mut u8)
 asm_func!(
     "wasmtime_fiber_switch",