bug#47067: 28.0.50; [feature/native-comp] Crash while scrolling through dispnew.c

[Pip Cet <pipcet@gmail.com>]

On Sat, Mar 13, 2021 at 11:10 AM Eli Zaretskii <eliz@gnu.org> wrote:
> > From: Pip Cet <pipcet@gmail.com>
> > Date: Sat, 13 Mar 2021 08:53:04 +0000
> > Cc: Andrea Corallo <akrl@sdf.org>, 47067@debbugs.gnu.org
> >
> > It's c-beginning-of-statement-1 that I think is the immediate caller.
>
> It's nowhere in the C backtrace, only its caller

But it was in one of the previous backtraces?

> c-font-lock-cut-off-declarators is.  And I'm not sure we can trust the
> C backtrace anyway, given its abnormalities that I cannot explain yet.

Good point.

> > Can you disassemble the function around 0x09c32285 (or, in another
> > dump, whatever calls Flss), particularly the 256 bytes or so before
> > that EIP?
>
> Below.  The updated address for the caller of Flss is 0x09d82285,
> which is not in any function whose name is known to GDB.

That's normal, assuming you didn't compile with comp-debug > 0.

> (gdb) disassemble 0x9d82100,+0x200
> Dump of assembler code from 0x9d82100 to 0x9d82300:
>    0x09d82100:  mov    %edx,-0xe4(%ebp)
>    0x09d82106:  mov    0x9e87564,%edx
>    0x09d8210c:  mov    %eax,-0xe0(%ebp)
>    0x09d82112:  mov    -0x100(%ebp),%eax
>    0x09d82118:  mov    %edx,-0xdc(%ebp)
>    0x09d8211e:  mov    %eax,0x4(%esp)
>    0x09d82122:  call   *0xd84(%ebx)
>    0x09d82128:  mov    %eax,-0xf0(%ebp)
>    0x09d8212e:  mov    %edx,-0xec(%ebp)
>    0x09d82134:  mov    %eax,(%esp)
>    0x09d82137:  mov    %edx,0x4(%esp)
>    0x09d8213b:  call   *0xad8(%ebx)
>    0x09d82141:  mov    %eax,-0xf0(%ebp)
>    0x09d82147:  mov    %edx,-0xec(%ebp)
>    0x09d8214d:  call   *0xab0(%ebx)
>    0x09d82153:  jmp    0x9d80934
>    0x09d82158:  lea    0x0(%esi,%eiz,1),%esi
>    0x09d8215f:  nop
>    0x09d82160:  mov    0x9e87b50,%eax
>    0x09d82165:  mov    0x9e87b54,%edx
>    0x09d8216b:  mov    %eax,-0xf0(%ebp)
>    0x09d82171:  mov    0x9e87aa0,%eax
>    0x09d82176:  mov    %edx,-0xec(%ebp)
>    0x09d8217c:  mov    0x9e87aa4,%edx
>    0x09d82182:  mov    %eax,(%esp)
>    0x09d82185:  mov    %edx,0x4(%esp)
>    0x09d82189:  call   *0x1358(%ebx)
>    0x09d8218f:  movl   $0x4,(%esp)
>    0x09d82196:  mov    %eax,-0xe8(%ebp)
>    0x09d8219c:  mov    0x9e875f0,%eax
>    0x09d821a1:  mov    %edx,-0xe4(%ebp)
>    0x09d821a7:  mov    0x9e875f4,%edx
>    0x09d821ad:  mov    %eax,-0xe0(%ebp)
>    0x09d821b3:  mov    %eax,-0xd8(%ebp)
>    0x09d821b9:  mov    -0x100(%ebp),%eax
>    0x09d821bf:  mov    %edx,-0xdc(%ebp)
>    0x09d821c5:  mov    %edx,-0xd4(%ebp)
>    0x09d821cb:  mov    %eax,0x4(%esp)
>    0x09d821cf:  call   *0xd84(%ebx)
>    0x09d821d5:  mov    0x9e8a750,%ecx
>    0x09d821db:  mov    %eax,-0xf0(%ebp)
>    0x09d821e1:  mov    (%ecx),%ecx
>    0x09d821e3:  mov    %edx,-0xec(%ebp)
>    0x09d821e9:  mov    0x54(%ecx),%esi
>    0x09d821ec:  mov    0x20(%esi),%esi
>    0x09d821ef:  mov    %esi,0x54(%ecx)
>    0x09d821f2:  jmp    0x9d808b2
>    0x09d821f7:  lea    0x0(%esi,%eiz,1),%esi
>    0x09d821fe:  xchg   %ax,%ax
>    0x09d82200:  mov    0x9e87950,%eax
>    0x09d82205:  mov    0x9e87954,%edx
>    0x09d8220b:  mov    %eax,(%esp)
>    0x09d8220e:  mov    %edx,0x4(%esp)
>    0x09d82212:  call   *0x1358(%ebx)
>    0x09d82218:  mov    %edx,-0xec(%ebp)
>    0x09d8221e:  or     %eax,%edx
>    0x09d82220:  mov    %eax,-0xf0(%ebp)
>    0x09d82226:  je     0x9d82308
>    0x09d8222c:  mov    0x9e87690,%eax
>    0x09d82231:  mov    0x9e87694,%edx
>    0x09d82237:  mov    %eax,(%esp)
>    0x09d8223a:  mov    %edx,0x4(%esp)
>    0x09d8223e:  call   *0x1358(%ebx)
>    0x09d82244:  mov    %eax,-0xf0(%ebp)
>    0x09d8224a:  mov    0x9e875a8,%eax
>    0x09d8224f:  mov    %edx,-0xec(%ebp)
>    0x09d82255:  mov    0x9e875ac,%edx
>    0x09d8225b:  mov    %eax,(%esp)
>    0x09d8225e:  mov    %edx,0x4(%esp)
>    0x09d82262:  call   *0x1358(%ebx)
>    0x09d82268:  mov    %edi,0x4(%esp)
>    0x09d8226c:  mov    %eax,-0xe8(%ebp)
>    0x09d82272:  mov    %edx,-0xe4(%ebp)
>    0x09d82278:  movl   $0x2,(%esp)
>    0x09d8227f:  call   *0x1318(%ebx)
>    0x09d82285:  mov    %edx,-0xec(%ebp)  <<<<<<<<<<<<<<<<<<<<

So EDI is bunk at this point. Can you go back a bit further to where
it's initialized?

> (gdb) info registers
> eax            0x30                48
> ecx            0x6a54fe8           111497192
> edx            0x8                 8
> ebx            0x187b8c0           25671872
> esp            0x826650            0x826650
> ebp            0x826778            0x826778
> esi            0x4002d2b0          1073926832
> edi            0x28                40

That value should be between 0x826650 and 0x826778.

Pip