[aaalloc]

From #27939

while compiling

#include <unistd.h>

int main(int argc, char **argv) {
  fsync(0);
  fdatasync(0);
  return 0;
}

You get

wasm-ld: error: import module mismatch for symbol: __wasi_fd_sync
>>> defined as env in /home/paradust/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/thinlto/libwasmfs-debug.a(syscalls.o)
>>> defined as wasi_snapshot_preview1 in /home/paradust/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/thinlto/minimal.wasm.lto.libc-debug.a(fsync.o at 2366516).o
emcc: error: '/home/paradust/emsdk/upstream/bin/wasm-ld -o minimal.wasm /tmp/tmp_mszapyplibemscripten_js_symbols.so -Bstatic --strip-debug -u__cxa_atexit --export=emscripten_stack_get_end --export=emscripten_stack_get_free --export=emscripten_stack_get_base --export=emscripten_stack_get_current --export=emscripten_stack_init --export=wasmfs_flush --export=_emscripten_stack_alloc --export=setThrew --export=__wasm_call_ctors --export=_emscripten_stack_restore --export-if-defined=__start_em_asm --export-if-defined=__stop_em_asm --export-if-defined=__start_em_lib_deps --export-if-defined=__stop_em_lib_deps --export-if-defined=__start_em_js --export-if-defined=__stop_em_js --export-if-defined=main --export-if-defined=__main_argc_argv --export-if-defined=fflush --export-table -z stack-size=65536 --no-growable-memory --initial-heap=16777216 --no-entry --stack-first --table-base=1 /tmp/emscripten_temp_8xy2kcjf/minimal.o -L/home/paradust/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/thinlto -L/home/paradust/emsdk/upstream/emscripten/src/lib -lGL-getprocaddr -lal -lhtml5 -lstubs-debug -lnoexit -lc-debug -ldlmalloc-debug -lclang_rt.builtins -lc++-debug-noexcept -lc++abi-debug-noexcept -lsockets -lwasmfs_no_fs -lwasmfs-debug -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr' failed (returned 1)

and thats because of this

>>> defined as env in /home/paradust/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/thinlto/libwasmfs-debug.a(syscalls.o)
>>> defined as wasi_snapshot_preview1 in /home/paradust/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/thinlto/minimal.wasm.lto.libc-debug.a(fsync.o at 2366516).o

It seems that fdatasync

int fdatasync(int fd)
{
     return syscall_cp(SYS_fdatasync, fd);
}
// system/lib/libc/musl/arch/emscripten/bits/syscall.h
#define SYS_fdatasync		__syscall_fdatasync


// system/lib/wasmfs/syscalls.cpp
int __syscall_fdatasync(int fd) {
  // TODO: Optimize this to avoid unnecessarily flushing unnecessary metadata.
  // Translate from WASI positive error codes to negative error codes.
  return -__wasi_fd_sync(fd);
}

is practically the same as fsync

int fsync(int fd)
{
#if __EMSCRIPTEN__
	return __wasi_syscall_ret(__wasi_fd_sync(fd));
#else
	return syscall_cp(SYS_fsync, fd);
#endif
}

but here we don't have SYS_fsync definition in system/lib/libc/musl/arch/emscripten/bits/syscall.h, so i assume it never goes into the else, and there you go you have your double definition

I followed how fsync is defined but maybe we can go the other way around by applying how fdatasync was to fsync, i don't know.

I have runned test with

test/runner.py 'other.test_unistd_fdatasync' \
               'other.test_fsync*' \
               'core0.test_unistd_misc*' \
               'lto0.test_unistd_misc*' \
               'lto2.test_unistd_misc*'

and everything pass

[gemini-code-assist]

Code Review

This pull request introduces an Emscripten-specific implementation for fdatasync using WASI's __wasi_fd_sync. The reviewer correctly pointed out a bug where a negative error code is passed to __wasi_syscall_ret, which expects a positive error code. This would result in errno being set to a negative value, violating POSIX standards. A code suggestion was provided to remove the minus sign.

[sbc100]

I feel like this error not correct and there is probably a fix on the llvm side that fixes the root cause here.. I'm looking into it now.

[sbc100]

I have a fix on the llvm side: llvm/llvm-project#239883

I'm still not if this is quite the right place to fix the issue..