On Thu, Nov 14, 2013 at 10:09 PM, Jakub Jelinek <ja...@redhat.com> wrote: > On Thu, Nov 14, 2013 at 07:08:17PM +0100, Jakub Jelinek wrote: >> On Thu, Nov 14, 2013 at 09:56:36PM +0400, Konstantin Serebryany wrote: >> > I thought about alignment but did not reflect it anywhere in the >> > interface/comments. >> > The alignment should be min(4096, N), which is enough for most purposes. >> >> You mean max(4096, N), right? > > Oops, of course min. > >> And, what exactly is N? 1 << (class_id + 6)?
Right. The minimal allocation unit is 64-aligned 64-bytes. Then 128-aligned 128-bytes and so on up to 4096. Then only 4096-alignment is guaranteed. These are the chunks returned by __asan_stack_malloc. The compiler pads them with redzones which in clang (and IIRC in gcc) are 32-aligned 32-bytes. You raised a valid concern about 512-bit (64-byte) alignment. Clang asan does not support that now (will just not add a redzone to such variables). Someday we'll implement adaptable redzones for stack (we did that for globals and heap already) which will fix this. --kcc > > But this is valid. > > Jakub
