On Sat, Feb 04, 2023 at 05:07:08AM -0800, Andres Freund wrote: > <source>: In function 'assign': > <source>:9:6: warning: array subscript 'foo[0]' is partly outside array > bounds of 'unsigned char[4]' [-Warray-bounds=] > 9 | p->i = i; > | ^~ > <source>:8:22: note: object of size 4 allocated by '__builtin_malloc' > 8 | foo *p = (foo *) __builtin_malloc(sizeof(int)); > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > Compiler returned: 0 > > I can't really tell if gcc is right or wrong wrong to warn about > this. On the one hand it's a union, and we only access the element that > is actually backed by memory, on the other hand, the standard does say > that the size of a union is the largest element, so we are pointing to > something undersized.
Something I have noticed, related to that.. meson reports a set of warnings here, not ./configure, still I apply the same set of CFLAGS to both. What's the difference in the meson setup that creates that, if I may ask? There is a link to the way -Warray-bound is handled? > We actually have a fair amount of code like that, but currently are > escaping most of the warnings, because gcc doesn't know that palloc() is > an allocator. With more optimizations (particularly with LTO), we end up > with more of such warnings. I'd like to annotate palloc so gcc > understands the size, as that does help to catch bugs when confusing the > type. It also helps static analyzers. Ah, that seems like a good idea in the long run. -- Michael
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