Re:Re: gdbserver for arm does not support multi-process debugging

[刘康 <lkang0305@163.com>]

Hi,
I see, maybe my gdbserver version is too old...I'll compile a latest version and try again.


Thank you so much for your help!

At 2019-10-24 18:38:46, "Luis Machado" <luis.machado@linaro.org> wrote:
>Hi,
>
>I just ran a quick check (foll-fork.exp and follow-vfork.exp tests) on a 
>arm machine and things worked as expected.
>
>What version of GDB/kernel are you using?
>
>On 10/24/19 2:32 AM, 刘康 wrote:
>> Hi Luis,
>> 
>> Yes, I know that gdbserver willcatch PTRACE_EVENT_FORK in 
>> gdb/gdbserver/linux-low.c:handle_extended_wait and get the child 
>> process's pid via PTRACE_GETEVENTMSG.
>> 
>> I found the way of X86 version gdb to deal with PTRACE_EVENT_FORKwill 
>> set waitstatus toTARGET_WAITKIND_FORKED and add a new inferior .What's 
>> more ,it can trace child/parent process automatically as long as I set 
>> "follow-fork-mode" to "child" or "parent".
>> 
>> But it seems like gdbserver will not tell PTRACE_EVENT_FORK to thehost 
>> arm-XXX-gdb this event ,as a result , user cannot trace child process or 
>> add a new inferior no matter what value of "detach-on-fork off" and 
>> "follow-fork-mode" I have tried.
>> 
>> At 2019-10-18 20:27:19, "Luis Machado" <luis.machado@linaro.org> wrote:
>>>Hi,
>>>
>>>On 10/17/19 3:19 AM, 刘康 wrote:
>>>> Dear gdb@sourceware.org
>>>> 
>>>> 
>>>> I am researching the gdbserver's source code for ARM, what confused me is that it does not support multi-process to debug the target's child process, cause it dose not interesting in PTRACE_EVENT_FORK, I don't know whether it's a bug or it's just a feature by design.
>>>
>>>The handling of PTRACE_EVENT_FORK, PTRACE_EVENT_VFORK and 
>>>PTRACE_EVENT_CLONE is in generic linux code. See 
>>>gdb/gdbserver/linux-low.c:handle_extended_wait.
>>>
>>>As long as the kernel supports reporting such events via ptrace and we 
>>>are debugging using extended remote mode (not regular remote mode), it 
>>>should work. If it doesn't, then we may have a problem that we should fix.
>>>
>>>Does that answer your question?
>>>
>>>Luis
>> 
>> 
>>