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H A D | stddef.h | 32a4ec21 Tue Sep 12 11:22:24 CDT 2023 Alexey Dobriyan <adobriyan@gmail.com> uapi: stddef.h: Fix __DECLARE_FLEX_ARRAY for C++
__DECLARE_FLEX_ARRAY(T, member) macro expands to
struct { struct {} __empty_member; T member[]; };
which is subtly wrong in C++ because sizeof(struct{}) is 1 not 0, changing UAPI structures layouts.
This can be fixed by expanding to
T member[];
Now g++ doesn't like "T member[]" either, throwing errors on the following code:
struct S { union { T1 member1[]; T2 member2[]; }; };
or
struct S { T member[]; };
Use "T member[0];" which seems to work and does the right thing wrt structure layout.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Fixes: 3080ea5553cc ("stddef: Introduce DECLARE_FLEX_ARRAY() helper") Link: https://lore.kernel.org/r/97242381-f1ec-4a4a-9472-1a464f575657@p183 Signed-off-by: Kees Cook <keescook@chromium.org>
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