On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds <torva...@linux-foundation.org> wrote: > On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf <jpoim...@redhat.com> wrote: >> >> Just to clarify, I think you're asking if, for versions of gcc which >> don't support -mpreferred-stack-boundary=3, objtool can analyze all C >> functions to ensure their stacks are 16-byte aligned. >> >> It's certainly possible, but I don't see how that solves the problem. >> The stack will still be misaligned by entry code. Or am I missing >> something? > > I think the argument is that we *could* try to align things, if we > just had some tool that actually then verified that we aren't missing > anything. > > I'm not entirely happy with checking the generated code, though, > because as Ingo says, you have a 50:50 chance of just getting it right > by mistake. So I'd much rather have some static tool that checks > things at a code level (ie coccinelle or sparse).
What I meant was checking the entry code to see if it aligns stack frames, and good luck getting sparse to do that. Hmm, getting 16-byte alignment for real may actually be entirely a lost cause. After all, I think we have some inline functions that do asm volatile ("call ..."), and I don't see any credible way of forcing alignment short of generating an entirely new stack frame and aligning that. Ick. This whole situation stinks, and I wish that the gcc developers had been less daft here in the first place or that we'd noticed and gotten it fixed much longer ago. Can we come up with a macro like STACK_ALIGN_16 that turns into __aligned__(32) on bad gcc versions and combine that with your sparse patch? -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html