[Bug sanitizer/61293] asan can not find left buffer overflow of new[]-allocated buffer, frontend help needed

["jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61293

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
IMNSHO you can't change the value of extra, that is an ABI issue,
and -fsanitize=address shouldn't be an ABI changing option.  Consider:
struct S { S (); ~S (); };
S *foo (int n) { return new S[n]; }
void bar (S *p) { delete [] p; }
int main () { bar (foo (5)); }
where bar is defined in a different compilation unit/library and something is
built with -fsanitize=address, something is not.

If the padding before structure is at least 64-bit, sure, instrumenting the FE
to put there an __asan_poison_memory_region call after the size is stored there
and in delete[] again to __asan_unpoison_memory_region before reading the size
should not be that hard.

For 32-bit code if the type doesn't need at least 64-bit alignment (again,
alignment of the type is an ABI thing), you are out of luck I'm afraid.
Thus, e.g. tests for this will need to be conditionalized.