----- Original Message -----
> At 09/23/2011 09:41 PM, Dave Anderson Write:
> >
> >
> > ----- Original Message -----
> >> If the task is a user program, the sp can be points to anywhere,
> >> because we can modify sp in assembly.
> >> For example:
> >>
> >> .globl main
> >> .type main, @function
> >> main:
> >>
> >> finit
> >> subq $16, (%rsp)
> >> movq $0, (%rsp)
> >> .loop:
> >> jmp .loop
> >>
> >>
> >
> > Why would any user task do that?
> >
> > And what happens when a backtrace is attempted on such a task?
> >
> > Since the current code would not set BT_USER_SPACE, I'm guessing that it
> > would run into this (at least on x86_64):
> >
> > if (!(bt->flags & BT_USER_SPACE) && (!rsp || !accessible(rsp))) {
> > error(INFO, "cannot determine starting stack pointer\n");
> > return;
> > }
>
> Yes, crash will run into this on x86_64.
OK, so why not change the above to do something like this:
if (!(bt->flags & BT_USER_SPACE) && (!rsp || !accessible(rsp))) {
fprintf(ofp, "cannot determine starting stack pointer\n");
if(KVMDUMP_DUMPFILE())
kvmdump_display_regs(bt->tc->processor, ofp);
else if (ELF_NOTES_VALID() && DISKDUMP_DUMPFILE())
diskdump_display_regs(bt->tc->processor, ofp);
else if (SADUMP_DUMPFILE()) {
sadump_display_regs(bt->tc->processor, ofp);
return;
}
Dave
> >
> > I do believe that I put the additional in_user_stack() checks in those
> > locations for a reason. Consider a task running in kernel mode that
> > corrupts its return address stack location with a non-kernel address,
> > or called a function indirectly that had a NULL pointer in it. That
> > would cause a kernel crash with a non-kernel RIP in its exception frame,
> > and your patch would mistake it for user-space.
>
> I know the reason why you check if sp is in user stack.
> What about this:
> if !is_kernel_text(ip) && (sp is in kernel stack(include irq))
> try to backtrace according to sp
> else
> display registers
>
> If both ip and sp is corrupted, and we can not determine sp according to
> the content in the stack, I think we should display registers.
>
> >
> > In any case, you're going to have to come up with a more compelling
> > reason to change all of these locations. (And for that matter, I wonder
> > why you didn't patch Fujitsu's get_sadump_regs() the same way?)
>
> No only for Fujitsu's sadump, I think kvmdump has the same problem.
>
> By the way, crash try to use the register when the dump format is diskdump.
> I think we should use the register value when the dump format is Fujitsu's
> sadump.
>
> Thanks
> Wen Congyang
>
> >
> > Dave
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