On Fri, 25 Jul 2014 13:01:11 -0700 Linus Torvalds <torva...@linux-foundation.org> wrote:
> For example, gcc will not create a small stack frame with "sub > $8,%rsp". No, what gcc does is to use a random "push" instruction. > Fair enough, but that really makes things much harder to see. Here's > an example: > > ffffffff813143a3 <dock_notify>: > ffffffff813143a3: 55 push %rbp > ffffffff813143a4: 48 89 e5 mov %rsp,%rbp > ffffffff813143a7: 41 57 push %r15 > ffffffff813143a9: 41 56 push %r14 > ffffffff813143ab: 49 89 fe mov %rdi,%r14 > ffffffff813143ae: 41 55 push %r13 > ffffffff813143b0: 41 89 f5 mov %esi,%r13d > ffffffff813143b3: 41 54 push %r12 > ffffffff813143b5: 53 push %rbx > ffffffff813143b6: 51 push %rcx > ... > ffffffff81314501: 48 8b 7e 08 mov 0x8(%rsi),%rdi > ffffffff81314505: 48 89 75 d0 mov %rsi,-0x30(%rbp) > ffffffff81314509: e8 5f d1 ff ff callq > ffffffff8131166d <acpi_bus_scan> > ffffffff8131450e: 85 c0 test %eax,%eax > ... > ffffffff813145d6: 5a pop %rdx > ffffffff813145d7: 5b pop %rbx > ffffffff813145d8: 44 89 e0 mov %r12d,%eax > ffffffff813145db: 41 5c pop %r12 > ffffffff813145dd: 41 5d pop %r13 > ffffffff813145df: 41 5e pop %r14 > ffffffff813145e1: 41 5f pop %r15 > ffffffff813145e3: 5d pop %rbp > ffffffff813145e4: c3 retq > > note the use (deep down in the function) of -0x30(%rbp), and note how > it does "pop %rdx" twice to undo the "push %rcx". It was just to > allocate space. I don't see a pop %rdx twice. Sure you're not suffering from a little dyslexia? ;-) But I do get your point. The rdx is popped where the rcx was, and both are useless, as rcx and rdx are volatile regs. > > So you definitely have to track the actual stack pointer updates, not > just the patterns of add/sub to %rsp. With Perl that would be rather trivial. I'm more concerned with branch logic. I'll see if I can include some simple branch logic too to flatten paths. But I wont really know the depth of this until I start hacking at it. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
