[Bug c/109956] GCC reserves 9 bytes for struct s { int a; char b; char t[]; } x = {1, 2, 3};

[amonakov at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109956

Alexander Monakov <amonakov at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |amonakov at gcc dot gnu.org

--- Comment #8 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
(In reply to jos...@codesourcery.com from comment #6)
> For the standard, dynamically allocated case, you should only need to 
> allocate enough memory to contain the initial part of the struct and the 
> array members being accessed - not any padding after that array.  (There 
> were wording problems before C99 TC2; see DR#282.)

I think the following testcase indicates that GCC assumes that tail padding is
accessible:

struct S {
        int i;
        char c;
        char fam[];
};

void f(struct S *p, struct S *q)
{
        *p = *q;
}

f:
        movq    (%rsi), %rax
        movq    %rax, (%rdi)
        ret

Sorry for the tangential remark, but there seems to be a contradiction.