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

[Luis Machado <luis.machado@linaro.org>]

On 10/29/19 10:43 PM, 刘康 wrote:
> Hmmm, I'll switch my gdbserver to a latest version.
> 
> Thank you so much and sorry for boring you with this.

Not a problem. The list is here for answering questions like these.

Luis

> 
> 
> At 2019-10-29 20:36:59, "Luis Machado" <luis.machado@linaro.org> wrote:
>>Hi,
>>
>> From reading the GDB NEWS file, proper support for gdbserver 
>>remote/extended-remote fork/vfork event reporting was included in GDB 
>>7.11, commit 19d9d4efd18bcc633e99cb6a3e39bd9b22ca70ce and others.
>>
>>I'd give a more recent GDB a try, since GDB 7.6 is mora than 5 years old 
>>now.
>>
>>On 10/29/19 7:42 AM, 刘康 wrote:
>>> Hi,
>>> My gdbserver andarm-linux-androideabi-gdbversion are both 7.6. and my 
>>> reproduction way is as follow:
>>> 
>>> 
>>> 
>>> and my gdbremotescript.gdb is
>>> 
>>> 
>>> the debug target "usb_upgrade_check" is the ELF of the source code 
>>> above(just ignore its strange name...it means nothing:-)     )
>>> 
>>> my target and host is communicating via TCP/IP protocol and my target 
>>> gdbserver launch parameter is
>>> 
>>> 
>>> my target's kernel version is 3.10.86
>>> 
>>> When everything is ready I do "set detach-on-fork off" and "set 
>>> follow-fork-mode child" at host and execute the continue command.
>>> The problem comes: host always has only one inferior which trace parent 
>>> process, no new inferior will be created and the child process could not 
>>> be traced in any way.
>>> I have also tried version 7.9 and the performance is the same.
>>> 
>>> My kernel and libc works well for syscall like ptrace and waitpid , 
>>> because I have make sure that the linux_test_for_tracefork() has no 
>>> problem by adding gdbserver some log.
>>> 
>>> At 2019-10-28 20:26:33, "Luis Machado" <luis.machado@linaro.org> wrote:
>>>>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_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
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>> 
>>> 
>>> 
> 
> 
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