Fix simd (default) build on clang >=16: undeclared libm fns in shim math.h - #1
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Fix simd (default) build on clang >=16: undeclared libm fns in shim math.h#1Leonardo-Rocha wants to merge 1 commit into
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The bundled wasm-sse2 compat headers (emscripten's SSE2->wasm128 shims, under shims/include/wasm-sse2/) reference fabs/lrint/lrintf/llrint/llrintf in their inline conversion helpers, but the freestanding shim math.h never declares them and stdb.rs exports only the float libm functions. clang 16 promoted -Wimplicit-function-declaration to a default error, so on any clang >= 16 a default (simd) build fails while parsing those headers: xmmintrin.h:600: error: call to undeclared function 'lrint' emmintrin.h:388: error: call to undeclared function 'fabs' Older clang (implicit decl = warning) or a toolchain whose own headers declare these hides the gap. It reproduces cleanly under zig cc (clang 18) in a strict -ffreestanding include setup where nothing leaks the decls. Add static inline definitions that lower to native wasm ops (f64.abs, f64.nearest + trunc conversions) — no libcall and no Rust-side libm export needed, so the fix is self-contained in the shim regardless of whether any path actually references them.
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Note: assisted by Claude Fable 5.
What
The bundled
wasm-sse2compat headers (emscripten's SSE2→wasm128 shims, undercrates/box3d-sys/shims/include/wasm-sse2/) referencefabs/lrint/lrintf/llrint/llrintfin their inline conversion helpers. But the freestanding shimmath.hnever declares them, andstdb.rsexports only the float libm functions (sinf…logf) — these five doubles are declared nowhere.Why it fails now
clang 16 promoted
-Wimplicit-function-declarationfrom a warning to a default error (the C99 non-conformance cleanup; GCC 14 followed). So a defaultcargo build—simdis on by default — hard-fails on any clang ≥16 while parsing those headers:It's a frontend diagnostic, not a link failure — the helpers are mostly unused and would be dropped at link, but the parse error fires regardless. It stays hidden on older clang (implicit-decl still a warning) or a toolchain whose own headers declare these ahead of the shim. Reproduces cleanly under
zig cc(clang 18) with a strict-ffreestandinginclude layout where nothing leaks the decls.The fix
Add static inline definitions to the shim
math.h. They lower to native wasm ops (f64.abs,f64.nearest+ trunc conversions) — no libcall, and no Rust-side libm export needed, so the fix is self-contained in the header. Zero behavior change for toolchains that already build: clang lowersfabs/lrintto the same native ops today; this only makes the declarations always visible.Alternatives considered
Bare
externdeclarations (matching the existing float-decl style) + exporting the doubles fromstdb.rslikesinf/etc. Works too, but needs a Rust export and a libcall; the inline-builtin form avoids both. Happy to switch to whichever you prefer for consistency.Verification (wasm32-unknown-unknown)
simddefault, clang 18 via zig cc): fails with the errors above.cargo build -p box3d-sys --target wasm32-unknown-unknowncompiles clean.Repro note (zig cc only)
If reproducing with
zig cc, also rewrite-isystem <dir>→-I <dir>for the shim dirs: zig prepends its bundled x86 intrinsic headers ahead of caller-isystemdirs and would otherwise shadow the compat shims with real x86 SSE2. Not relevant to the fix itself — noted in case it helps anyone verifying.