https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109956
--- Comment #11 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Alexander Monakov from comment #8) > (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. Not only accessible but also not used by sth else. That is, a following 'char' variable may not be placed into the padding.