8ac685ff84
Provides the libc / libcxx / libm symbols that the wasm32-unknown-
unknown skia static archive (built via vendor/skia-safe-op) imports
at link time but wasm-bindgen does not synthesize. With this crate
linked in, the post-bindgen bundle has 0 env.* imports and is
runtime-loadable as a vanilla browser ES module.
Categories implemented (~83 symbols, dedup against the actual
import list):
- allocator: malloc / free / calloc / realloc / malloc_usable_size
via dlmalloc-rs + a 16-byte size header per allocation so the
GlobalAlloc::dealloc layout contract is preserved on free and
realloc copies min(old_size, new_size) on grow
- libm: asinh / acosh / atanh / nextafterf / remainder via libm
- libc string: memchr / wmemchr / strcmp / strcpy / strtoull
hand-rolled byte-wise
- libc stdio: snprintf / vsnprintf / vfprintf as C-side variadic
stubs (stdio_stub.c, compiled by cc) that route into a Rust
extern wasm_libc_shim_stdio_panic before returning, so any
actual invocation surfaces a named panic via console_error_
panic_hook instead of a silent empty success
- libc misc: abort (panics with diagnostic) + __errno_location
(single-mut-static — single-threaded wasm only)
- C++ ABI: __cxa_atexit (no-op), __cxa_guard_acquire / release,
__cxa_pure_virtual (panics)
- operator new / delete: _Znwm / _Znam / _ZdlPv* / _ZdaPv*
forwarding to malloc / free; _Znwm(0) routes through
malloc(1) per C++ standard (operator new must return a
non-null pointer)
- threads: sem_init / sem_destroy / sem_post / sem_wait no-op
- libcxx string / locale / iostream / shared_weak_count /
to_string: ~23 panic stubs via the libcxx_stub! macro that
panic with the symbol name; these are linker-pulled by
templated code that the skia raster + custom_empty fontmgr
pipeline does not exercise at runtime, so a panic = regression
signal
Build-time gating:
- active only on wasm32-unknown-unknown via cfg(all(target_arch
= "wasm32", target_os = "unknown")); native builds link an
empty crate so the symbols do not collide with the host libc
- compile_error! on target_feature = "atomics" because the
static-mut errno + non-atomic __cxa guard impls would race
under wasm threads — the path forward is real TLS errno +
atomic guard variables in a follow-up sub-phase
Step 1b §3.2 P0.5B Run path, sub-phase C-hard.2.
38 lines
1.3 KiB
Rust
38 lines
1.3 KiB
Rust
// Compile the C-variadic stdio stubs for wasm32-unknown-unknown.
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// On any other target this is a no-op so the crate links empty.
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fn main() {
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let target = std::env::var("TARGET").unwrap_or_default();
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if target != "wasm32-unknown-unknown" {
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return;
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}
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let emsdk = match std::env::var("EMSDK") {
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Ok(v) => v,
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Err(_) => panic!(
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"wasm-libc-shim requires the EMSDK env var pointing at an emsdk install \
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(used only for libcxx headers + emsdk's bundled wasm32-aware clang)"
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),
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};
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let llvm_bin = format!("{emsdk}/upstream/emscripten/llvm/bin");
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let sysroot = format!("{emsdk}/upstream/emscripten/cache/sysroot");
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let mut build = cc::Build::new();
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build
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.compiler(format!("{llvm_bin}/clang"))
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.archiver(format!("{llvm_bin}/llvm-ar"))
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.file("src/stdio_stub.c")
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.flag(format!("--sysroot={sysroot}"))
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.flag(format!("-isystem{sysroot}/include"))
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.flag(format!("-isystem{sysroot}/include/compat"))
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.flag("--target=wasm32-unknown-unknown")
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.flag("-fvisibility=default")
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.flag("-fno-exceptions")
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.flag("-O2")
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.opt_level(2)
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.warnings(false);
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build.compile("wasm_libc_shim_stdio");
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println!("cargo:rerun-if-changed=src/stdio_stub.c");
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println!("cargo:rerun-if-env-changed=EMSDK");
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}
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