Re: [Regression] Segfault on native-extended-gdbserver + fork

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2018-01-29 11:00, Pedro Alves wrote:
> On 01/28/2018 04:50 PM, Simon Marchi wrote:
>> On 2018-01-28 01:32, Sergio Durigan Junior wrote:
> 
>> I'm fine with this, but I was curious about what happens in Pedro's 
>> multi-target branch.  I remember he said that the detach_inferior(int) 
>> version disappears in that branch, though I can't find where he said 
>> that.  But looking at the branch I can see it's indeed the case:
>> 
>>   
>> https://github.com/palves/gdb/blob/palves/multi-target/gdb/inferior.c#L250
>> 
>> So I was wondering what remote_follow_fork calls in that case, since 
>> it can't call the detach_inferior(inferior *) version without an 
>> inferior.  Apparently it calls a new remote_detach_pid function:
>> 
>>   
>> https://github.com/palves/gdb/blob/palves/multi-target/gdb/remote.c#L5859
> 
> remote_detach_pid is not new.  It exists in master.  What that url 
> shows
> is that I commented out the detach_inferior call in the branch.
> 
> Because in this case, we'd detaching a remote process that the core
> of gdb never learned about.

Oops I read that wrong.

>> 
>> This means (I just tried it) that it won't show the "[Inferior %d 
>> detached]\n" message in that case.  So what I would suggest is putting
>> 
>>   if (print_inferior_events)
>>     printf_unfiltered (_("[Inferior %d detached]\n"), pid);
>> 
>> in its own function, called by both versions of detach_inferior for 
>> now (bonus, it de-duplicates the printing of the message).  In the 
>> multi-target branch, remote_target::follow_fork (renamed from 
>> remote_follow_fork) can call this function in the case where we don't 
>> have an inferior object.
> 
> But why would we want to print that?  We will have already printed
> 
>   "Detaching after fork from child process PID."
> 
> from the common code.  When native debugging, in this scenario,
> we don't call detach_inferior either, right?  Can't see why
> we'd want to call it for remote.

It's true that it's a bit of a lie to say "[Inferior PID detached]" if 
there never actually was an inferior for that PID.  Since we never print 
"[Inferior PID detached]" on native in that case, I am fine with 
removing the call from remote.c.  Sergio, that would fix the crash you 
found I think?

Simon