Re: Regression in 2.6.25-rc3: s2ram segfaults before suspending

Klaus S. Madsen
2008-02-28T15:04:54Z

On Thu, Feb 28, 2008 at 10:40:00 +0100, Ingo Molnar wrote:
>
> * Klaus S. Madsen <ksm@hjernemadsen.org> wrote:
>
> > > > 524 int r;
> > > > 525 #ifdef __PIC__
> > > > 526 asm volatile (
> > > > 527 "pushl %%ebx\n\t"
> > > > 528 "movl %2, %%ebx\n\t"
> > > > 529 "int $0x80\n\t"
> > > > 530 "popl %%ebx"
> > > > (gdb) bt
> > > > #0 0xb7facf4a in run_vm86 () at lrmi.c:526
> > > > #1 0xb7fad61b in LRMI_int (i=16, r=0xbffca670) at lrmi.c:844
> > > > #2 0x0804acfc in do_vbe_service (AX=20227, BX=0, regs=0xbffca670)
> > > > at vbetool/vbetool.c:158
> > > > #3 0x0804af7e in __get_mode () at vbetool/vbetool.c:453
> > > > #4 0x0804a30f in s2ram_hacks () at s2ram-x86.c:268
> > > > #5 0x0804954f in main (argc=1, argv=0x0) at s2ram-main.c:92

[snip]

> > > thanks for tracking this down. It would be nice to figure out why this
> > > change made a difference. Perhaps VM86 mode has some restrictions in
> > > what type of pagetables it can operate in - and the CPU just refuses to
> > > properly emulate those 16-bit instructions? (this would be very weird).
> > > We are trying to execute 16-bit BIOS code here, right?
> > >
> > > which instruction is the segfault coming from - the int $0x80? So in
> > > vm86 mode we generated a #GPF which shows up as a SIGSEGV?

The segfault was at address 0xb7f59f4a, and the disassembly of
the run_vm86 function is:

0xb7f59f20 <run_vm86+0>: push %ebp
0xb7f59f21 <run_vm86+1>: mov %esp,%ebp
0xb7f59f23 <run_vm86+3>: push %edi
0xb7f59f24 <run_vm86+4>: push %esi
0xb7f59f25 <run_vm86+5>: push %ebx
0xb7f59f26 <run_vm86+6>: call 0xb7f59697 <__i686.get_pc_thunk.bx>
0xb7f59f2b <run_vm86+11>: add $0x18b5,%ebx
0xb7f59f31 <run_vm86+17>: sub $0x3c,%esp
0xb7f59f34 <run_vm86+20>: lea 0x48c(%ebx),%eax
0xb7f59f3a <run_vm86+26>: mov %eax,0xffffffc0(%ebp)
0xb7f59f3d <run_vm86+29>: mov $0x71,%eax
0xb7f59f42 <run_vm86+34>: mov 0xffffffc0(%ebp),%ecx
0xb7f59f45 <run_vm86+37>: push %ebx
0xb7f59f46 <run_vm86+38>: mov %ecx,%ebx
0xb7f59f48 <run_vm86+40>: int $0x80
0xb7f59f4a <run_vm86+42>: pop %ebx
0xb7f59f4b <run_vm86+43>: mov %eax,%edx
0xb7f59f4d <run_vm86+45>: and $0xff,%eax
0xb7f59f52 <run_vm86+50>: cmp $0x2,%eax
0xb7f59f55 <run_vm86+53>: je 0xb7f5a0b5 <run_vm86+405>
0xb7f59f5b <run_vm86+59>: sub $0x1,%eax
0xb7f59f5e <run_vm86+62>: jne 0xb7f5a28a <run_vm86+874>

Hope this helps.

--
Kind regards
Klaus S. Madsen