Re: git-blame segfault

From: Markus Trippelsdorf <markus@trippelsdorf.de>
Date: Dec 3, 2013, 08:45 UTC
Message-ID: <20131203084540.GA276@x4>
In-Reply-To: <20131202150541.GB275@x4>

On 2013.12.02 at 16:05 +0100, Markus Trippelsdorf wrote:

Show 36 quoted lines

> On 2013.12.02 at 15:15 +0100, Antoine Pelisse wrote:
> > Would that mean that gcc is doing some steps in the wrong order ? That
> > is setting xecfg.hunk_func and then emptying the structure ? I've
> > already had a similar bug, but that's very unfortunate.
> 
> Yes. I think this might be the case:
> 
> (gdb) disass
> Dump of assembler code for function diff_hunks:
>    0x0000000000410460 <+0>:     sub    $0x58,%rsp
>    0x0000000000410464 <+4>:     xor    %eax,%eax
>    0x0000000000410466 <+6>:     mov    %eax,%r9d
>    0x0000000000410469 <+9>:     add    $0x20,%eax
>    0x000000000041046c <+12>:    cmp    $0x20,%eax
>    0x000000000041046f <+15>:    movq   $0x0,0x20(%rsp,%r9,1)
>    0x0000000000410478 <+24>:    movq   $0x0,0x28(%rsp,%r9,1)
>    0x0000000000410481 <+33>:    movq   $0x0,0x30(%rsp,%r9,1)
>    0x000000000041048a <+42>:    movq   $0x0,0x38(%rsp,%r9,1)
>    0x0000000000410493 <+51>:    jb     0x410466 <diff_hunks+6>
>    0x0000000000410495 <+53>:    lea    0x20(%rsp),%r10
>    0x000000000041049a <+58>:    mov    %rdx,0x20(%rsp)
>    0x000000000041049f <+63>:    mov    %rcx,0x48(%rsp)
>    0x00000000004104a4 <+68>:    add    %r10,%rax
>    0x00000000004104a7 <+71>:    mov    %r8,0x10(%rsp)
>    0x00000000004104ac <+76>:    mov    %rsp,%rdx
>    0x00000000004104af <+79>:    movq   $0x0,(%rax)
>    0x00000000004104b6 <+86>:    movq   $0x0,0x8(%rax)
>    0x00000000004104be <+94>:    lea    0x10(%rsp),%r8
>    0x00000000004104c3 <+99>:    movslq 0x171882(%rip),%rax        # 0x581d4c <xdl_opts>
>    0x00000000004104ca <+106>:   mov    %r10,%rcx
>    0x00000000004104cd <+109>:   movq   $0x0,0x18(%rsp)
>    0x00000000004104d6 <+118>:   mov    %rax,(%rsp)
>    0x00000000004104da <+122>:   callq  0x50aee0 <xdi_diff>
> => 0x00000000004104df <+127>:   add    $0x58,%rsp
>    0x00000000004104e3 <+131>:   retq   
> End of assembler dump.

Should be fixed in gcc soon. For the curious, here is the assembler diff (bad vs. good):

        .type   diff_hunks, @function
 diff_hunks:
 .LFB104:
        .cfi_startproc
        subq    $88, %rsp
        .cfi_def_cfa_offset 96
        xorl    %eax, %eax
 .L31:
        movl    %eax, %r9d
        addl    $32, %eax
        cmpl    $32, %eax
        movq    $0, 32(%rsp,%r9)
        movq    $0, 40(%rsp,%r9)
        movq    $0, 48(%rsp,%r9)
        movq    $0, 56(%rsp,%r9)
        jb      .L31
        leaq    32(%rsp), %r10
        movq    %rdx, 32(%rsp)
-       movq    %rcx, 72(%rsp)
-       addq    %r10, %rax
        movq    %r8, 16(%rsp)
+       addq    %r10, %rax
+       leaq    16(%rsp), %r8
        movq    %rsp, %rdx
-       movq    $0, (%rax)
        movq    $0, 8(%rax)
-       leaq    16(%rsp), %r8
+       movq    $0, (%rax)
        movslq  xdl_opts(%rip), %rax
+       movq    %rcx, 72(%rsp)
        movq    %r10, %rcx
        movq    $0, 24(%rsp)
        movq    %rax, (%rsp)
        call    xdi_diff
        addq    $88, %rsp
        .cfi_def_cfa_offset 8

-- 
Markus