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Re: "finish" command leads to SIGTRAP
It's something to do with the nature of single stepping through a "popfq"
instruction. Given the following instructions:
0x7fffe104638f: add $0x8,%rsp
0x7fffe1046393: popfq
0x7fffe1046394: pop %rbp
0x7fffe1046395: jmpq *%rax
If I set a breakpoint at the first of that set and single step through, I
end up with:
eflags 0x346 [ PF ZF TF IF ]
but if I set a breakpoint on the last instruction and avoid single stepping
I get:
eflags 0x246 [ PF ZF IF ]
and I think it's that TF that is causing the SIGTRAP?
On Thu, 21 Feb 2019 at 13:12, Pedro Alves <palves@redhat.com> wrote:
> Might be unrelated, but ISTR that there used to be a kernel bug
> that would lead to the cpu's trace flag getting stuck set
> when you step in a signal handler. That would result in
> SIGTRAP happening at every step from that point on. Could
> that be the case here?
>
> I'd look at "set debug displaced on" too. Otherwise, it's a matter
> at staring at the logs, and trying to understand what is happening.
> Basically, "finish" sets a breakpoint at the caller and runs to it.
> But all sorts of other things can happen behind the scenes.
>
> Thanks,
> Pedro Alves
>
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