Re: [PATCH] Remove lwp -> pid conversion in linux_nat_xfer_partial

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

On 2017-03-21 21:00, Pedro Alves wrote:
> Nope.  If you call "exit", then yes.  The kernel kills the whole thread
> group in response to that system call.  If the leader does
> pthread_exit, then no, the thread group stays around until all children
> exit too.  The kernel won't report the main thread's exit status (i.e.,
> we can't reap that zombie, and we'd hang if we tried a blocking 
> waitpid)
> until all the children are reaped first.  That's why we have
> linux-nat.c:check_zombie_leaders (and the equivalent in gdbserver).

Oh ok, in my testing I was just letting main return, but I guess it 
reaches a point where the libc calls the exit syscall.  When I call 
pthread_exit, the process stays alive.

>>> So if possible to switch those spots too, I'd recommend/prefer it.
>> 
>> Ok, I'll just replace ptid_get_pid with get_ptrace_pid* in this patch
> 
> Since this is linux-specific code, you should be able to use
> ptid_get_lwp directly.

Ok.

>> and look at using /proc/<pid>/task/<tid> after.  When doing the 
>> latter,
>> do I still have to consider cases where ptid is a 
>> single-process/thread
>> ptid (lwp == 0)?  From my experience, there's always a lwp on Linux, 
>> but
>> perhaps there are some setups I don't know about with which it can 
>> happen?
> 
> Right, on Linux there's always an lwp.  Before NPTL, the
> /proc/<pid>/task/<tid> path didn't exist at all, but we no longer
> support LinuxThreads.

Thanks, I'm sending an updated patch.

Simon