Re: single-step SIGALRM issue

[teawater <teawater@gmail.com>]

This is because GDB think SIGALRM is a random signal.
Maybe command "handle SIGALRM stop print nopass" can deal with it.

On Wed, Jan 21, 2009 at 16:22, Laszlo Benedek <laszlo.benedek@gmail.com> wrote:
> No, we don't use RSP, we simply start our program with gdb. Did you
> mean that by linking together?
> I know why the SIGALRM signals come, my original question was why gdb
> fails to single step our program when the SIGALRM signals come instead
> of the SIGTRAP.
>
> Best regards,
> Laszlo Benedek
>
> On Wed, Jan 21, 2009 at 8:31 AM, teawater <teawater@gmail.com> wrote:
>> How do your simulator work with GDB? Link together or connect with RSP?
>>
>> I think maybe "It uses the SIGALRM signal to simulate interrupts."
>> this is the reason you got SIGALRM.
>>
>> On Wed, Jan 21, 2009 at 15:16, Laszlo Benedek <laszlo.benedek@gmail.com> wrote:
>>> I am afraid I don't understand your question. What do you mean by
>>> returning a SIGTRAP?
>>> GDB receives the signals from the OS, not my program sends them.
>>>
>>> On Wed, Jan 21, 2009 at 7:17 AM, teawater <teawater@gmail.com> wrote:
>>>> "it is expecting a SIGTRAP signal but sometimes it receives a SIGALRM
>>>> instead."
>>>>
>>>> Why you can't aways return SIGTRAP?
>>>>
>>>> On Tue, Jan 20, 2009 at 01:50, Laszlo Benedek <laszlo.benedek@gmail.com> wrote:
>>>>> Hi,
>>>>>
>>>>> I am part of a team developing a simulator and we have problems
>>>>> debugging the simulator with gdb.
>>>>> The simulator is an application written for x86-linux and it was
>>>>> written in c/c++.
>>>>> It uses the SIGALRM signal to simulate interrupts.
>>>>>
>>>>> The test that fails:
>>>>> I start the simulator in gdb and insert a breakpoint at a certain function call.
>>>>> When the program reaches the breakpoint it correctly stops, then I try
>>>>> to use single stepping.
>>>>> At this point something wierd happens, sometimes it works fine and I
>>>>> can use the step command
>>>>> but sometimes the program starts to run and then hangs.
>>>>>
>>>>> I tried to find the reason of this and here is what I've found. When
>>>>> gdb starts single stepping
>>>>> it is expecting a SIGTRAP signal but sometimes it receives a SIGALRM
>>>>> instead. In this case it
>>>>> decides to switch the inferior in 'continue' mode, inserts a
>>>>> breakpoint and waits. In this case our
>>>>> program continues to run from the original breakpoint and eventually
>>>>> it reaches a point where it calls sigsuspend
>>>>> and it waits for signals but it does not receive any signals anymore.
>>>>> It seems that gdb is blocking them somehow
>>>>> when this single-step => continue switch happens. I read the comment
>>>>> in the gdb source and it says that gdb expects
>>>>> that the program's signal handler will be called and it will stop at
>>>>> the return of the signal handler because gdb just
>>>>> inserted a breakpoint there. For some reason the signal handler of our
>>>>> program is not called at all after it gets into this 'continue' mode.
>>>>>
>>>>> I'd like to fix this or at least decide if this is an error in gdb or
>>>>> in the simulator (or both?), but I don't really know how to continue.
>>>>> Has anyone experienced anything like this before ?
>>>>> Any comment, idea would be appreciated.
>>>>>
>>>>> Thanks for your help in advance!
>>>>>
>>>>> Best regards,
>>>>> Laszlo Benedek
>>>>>
>>>>
>>>
>>
>