clang-tidy的altera-struct-pack-align建议与GCC警告冲突是否为Bug？

I ran a full set of clang-tidy checks alongside GCC and hit a frustrating contradiction: the fix recommended by clang-tidy for a padding warning triggers a valid warning from GCC. This looks like a clear bug in the altera-struct-pack-align check.

Minimal Reproducible Example #

struct a{ virtual void func()=0; virtual void func2()=0; };
struct b:a{ void func() override {}; void func2() override {}; private: int x{}; };
int main(){ b b_item; }

Clang-Tidy Output #

/home/main.cpp:7:8: note: use "attribute((aligned(0)))" to align struct 'a' to 0 bytes
struct a{^
/home/main.cpp:13:8: warning: accessing fields in struct 'b' is inefficient due to padding; only needs 4 bytes but is using 16 bytes [altera-struct-pack-align]
struct b:a{^

After Applying Clang-Tidy's Fix #

struct a{ virtual void func()=0; virtual void func2()=0; } __attribute__((aligned(0)));
struct b:a{ void func() override {}; void func2() override {}; private: int x{}; };
int main(){ b b_item; }

GCC Warning Triggered by the Fix #

warning: requested alignment ‘0’ is not a positive power of 2 [-Wattributes]
12 | } attribute((aligned(0)));

Analysis #

The problem here is that clang-tidy's altera-struct-pack-align check is suggesting an alignment value that's invalid for GCC. GCC requires the aligned attribute argument to be a positive integer that's a power of 2—using 0 directly violates this rule, hence the warning.

This is a bug in the clang-tidy check: it generates a fix that's incompatible with GCC, even though the original code compiles cleanly with the compiler. The check should either avoid recommending aligned(0) when targeting GCC, or use a valid alignment value that addresses the padding concern without triggering compiler warnings.

内容的提问来源于stack exchange，提问作者Spyros Mourelatos