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.
30 lines
909 B
TOML
30 lines
909 B
TOML
[package]
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name = "wasm-libc-shim"
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version.workspace = true
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edition.workspace = true
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rust-version.workspace = true
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license.workspace = true
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description = "C-hard.2 — minimal libc / libcxx / libm shim for wasm32-unknown-unknown skia bundles (Step 1b §3.2 P0.5B Run path)"
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[lib]
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name = "wasm_libc_shim"
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path = "src/lib.rs"
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[dependencies]
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# Pure-Rust no_std allocator with a wasm32 backend; satisfies the
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# malloc/free/calloc/realloc/malloc_usable_size import family.
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dlmalloc = { version = "0.2", features = ["global"] }
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# Pure-Rust no_std math; satisfies asinh/acosh/atanh/nextafterf/remainder.
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libm = "0.2"
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[build-dependencies]
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# Compile a tiny C stub for the variadic snprintf / vsnprintf / vfprintf
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# trio. Stable Rust does not allow `extern "C" fn(...)` with C-variadic
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# without the `c_variadic` feature; using a 5-line .c file keeps the
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# crate stable-compatible.
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cc = "1"
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[features]
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default = []
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