__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: 3080ea5553 ("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>
32a4ec211d