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bootstrap: disable strict aliasing

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The C backend has always gleefully violated C's strict aliasing rules,
and I just got bitten by it for the first time when bootstrapping on
macOS. This probably hasn't been helping with some of the weird
bootstrap-related CI failures we've seen. So, update `bootstrap.c` and
`CMakeLists.txt` to tell GCC/Clang to disable type-based alias analysis.

No change is needed to the MSVC flags because MSVC does not, and never
has, implemented TBAA.
This commit is contained in:
Matthew Lugg
2026-03-09 12:02:58 +00:00
parent 57114044db
commit 79e7b719a3
2 changed files with 4 additions and 3 deletions
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CMakeLists.txt
+2 -2
View File
@@ -608,8 +608,8 @@ if(MSVC)
set(ZIG2_LINK_FLAGS "/STACK:16777216 /FORCE:MULTIPLE")
else()
set(ZIG_WASM2C_COMPILE_FLAGS "-std=c99 -O2")
set(ZIG1_COMPILE_FLAGS "-std=c99 -Os")
set(ZIG2_COMPILE_FLAGS "-std=c99 -O0 -fno-sanitize=undefined -fno-stack-protector")
set(ZIG1_COMPILE_FLAGS "-std=c99 -Os -fno-strict-aliasing")
set(ZIG2_COMPILE_FLAGS "-std=c99 -O0 -fno-sanitize=undefined -fno-stack-protector -fno-strict-aliasing")
# Must match the condition in build.zig.
if(ZIG_HOST_TARGET_ARCH MATCHES "^(arm|thumb)(eb)?$" OR ZIG_HOST_TARGET_ARCH MATCHES "^powerpc(64)?(le)?$")
set(ZIG1_COMPILE_FLAGS "${ZIG1_COMPILE_FLAGS} -ffunction-sections -fdata-sections")
bootstrap.c
+2 -1
View File
@@ -136,7 +136,7 @@ int main(int argc, char **argv) {
}
{
const char *child_argv[] = {
cc, "-o", "zig1", "zig1.c", "stage1/wasi.c", "-std=c99", "-Os", "-lm", NULL,
cc, "-o", "zig1", "zig1.c", "stage1/wasi.c", "-std=c99", "-Os", "-fno-strict-aliasing", "-lm", NULL,
};
print_and_run(child_argv);
}
@@ -213,6 +213,7 @@ int main(int argc, char **argv) {
#if defined(__GNUC__)
"-pthread",
#endif
"-fno-strict-aliasing",
workaround_gcc_sra_miscomp ? "-fno-tree-sra" : NULL,
NULL,
};