| Message ID | CAFULd4b5gA0VgTiMzrFnY+tRKjNUoDDqJm7C1_PxENPfQ1dVzg@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
On 02/13/2012 02:54 PM, Uros Bizjak wrote: > - movq 56(%rsi), %rdx > movl %edi, %eax > cfi_def_cfa(%rcx, 0) > - cfi_register(%rip, %rdx) > movq %rcx, %rsp > - jmp *%rdx > + jmp *56(%rsi) If you're going to do that, the correct fix for the unwind info is - cfi_register(%rip, %rdx) + cfi_offset(%rip, 56) Otherwise ok. r~
On Mon, Feb 13, 2012 at 11:57 PM, Richard Henderson <rth@redhat.com> wrote: > On 02/13/2012 02:54 PM, Uros Bizjak wrote: >> - movq 56(%rsi), %rdx >> movl %edi, %eax >> cfi_def_cfa(%rcx, 0) >> - cfi_register(%rip, %rdx) >> movq %rcx, %rsp >> - jmp *%rdx >> + jmp *56(%rsi) > > If you're going to do that, the correct fix for the unwind info is > > - cfi_register(%rip, %rdx) > + cfi_offset(%rip, 56) Hm, we just defined new CFA as rcx+0, so we should define location of rip relative to new CFA. Since CFA points to stack slot just before return address was pushed, new rip lies at CFA-8 for 64bit resp. CFA-4 for x86_32. Did I get these .cfi directives correctly? SYM(GTM_longjmp): cfi_startproc #ifdef __x86_64__ movq (%rsi), %rcx movq 8(%rsi), %rbx movq 16(%rsi), %rbp movq 24(%rsi), %r12 movq 32(%rsi), %r13 movq 40(%rsi), %r14 movq 48(%rsi), %r15 movl %edi, %eax cfi_def_cfa(%rcx, 0) cfi_offset(%rip, -8) movq %rcx, %rsp jmp *56(%rsi) #else movl (%edx), %ecx movl 4(%edx), %ebx movl 8(%edx), %esi movl 12(%edx), %edi movl 16(%edx), %ebp cfi_def_cfa(%ecx, 0) cfi_offset(%eip, -4) movl %ecx, %esp jmp *20(%edx) #endif cfi_endproc Uros.
On 02/13/2012 04:09 PM, Uros Bizjak wrote: > On Mon, Feb 13, 2012 at 11:57 PM, Richard Henderson <rth@redhat.com> wrote: >> On 02/13/2012 02:54 PM, Uros Bizjak wrote: >>> - movq 56(%rsi), %rdx >>> movl %edi, %eax >>> cfi_def_cfa(%rcx, 0) >>> - cfi_register(%rip, %rdx) >>> movq %rcx, %rsp >>> - jmp *%rdx >>> + jmp *56(%rsi) >> >> If you're going to do that, the correct fix for the unwind info is >> >> - cfi_register(%rip, %rdx) >> + cfi_offset(%rip, 56) > > Hm, we just defined new CFA as rcx+0, so we should define location of > rip relative to new CFA. Since CFA points to stack slot just before > return address was pushed, new rip lies at CFA-8 for 64bit resp. CFA-4 > for x86_32. Did I get these .cfi directives correctly? No. The value at %rcx-8 is total garbage. There no guarantee that the call stack leading to this abort has anything in common with the call stack that created the jmpbuf, except *above* %rcx, the new CFA. The new rip is at rsi+56. You can see that in that you jump to it. r~
On Tue, Feb 14, 2012 at 1:15 AM, Richard Henderson <rth@redhat.com> wrote: >>>> - movq 56(%rsi), %rdx >>>> movl %edi, %eax >>>> cfi_def_cfa(%rcx, 0) >>>> - cfi_register(%rip, %rdx) >>>> movq %rcx, %rsp >>>> - jmp *%rdx >>>> + jmp *56(%rsi) >>> >>> If you're going to do that, the correct fix for the unwind info is >>> >>> - cfi_register(%rip, %rdx) >>> + cfi_offset(%rip, 56) >> >> Hm, we just defined new CFA as rcx+0, so we should define location of >> rip relative to new CFA. Since CFA points to stack slot just before >> return address was pushed, new rip lies at CFA-8 for 64bit resp. CFA-4 >> for x86_32. Did I get these .cfi directives correctly? > > No. The value at %rcx-8 is total garbage. There no guarantee that > the call stack leading to this abort has anything in common with the > call stack that created the jmpbuf, except *above* %rcx, the new CFA. > > The new rip is at rsi+56. You can see that in that you jump to it. Thanks for the explanation, I will commit the patch with your suggested change. Uros.
Index: config/x86/sjlj.S =================================================================== --- config/x86/sjlj.S (revision 184177) +++ config/x86/sjlj.S (working copy) @@ -119,23 +119,19 @@ SYM(GTM_longjmp): movq 32(%rsi), %r13 movq 40(%rsi), %r14 movq 48(%rsi), %r15 - movq 56(%rsi), %rdx movl %edi, %eax cfi_def_cfa(%rcx, 0) - cfi_register(%rip, %rdx) movq %rcx, %rsp - jmp *%rdx + jmp *56(%rsi) #else movl (%edx), %ecx movl 4(%edx), %ebx movl 8(%edx), %esi movl 12(%edx), %edi movl 16(%edx), %ebp - movl 20(%edx), %edx cfi_def_cfa(%ecx, 0) - cfi_register(%eip, %edx) movl %ecx, %esp - jmp *%edx + jmp *20(%edx) #endif cfi_endproc
Hello! We can jump indirect from memory address, sparing a couple of cycles. 2012-02-14 Uros Bizjak <ubizjak@gmail.com> * config/x86/target.h (GTM_longjmp): Jump indirect from memory address. Tested on x86_64-pc-linux-gnu {,-m32}. OK for mainline? Uros.