gdbserver for arm does not support multi-process debugging

[Luis Machado]

Do let us know what you see. If it still doesn't work with the most 
recent versions, it may be a real bug somewhere (not necessarily in 
gdb/gdbserver).

On 10/28/19 8:12 AM, 刘康 wrote:
> 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_FORKEDÂ 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
>>> 
>>> 
>>> 
> 
> 
>