Re: Fixing UML against NPTL (was: Re: [uml-devel] [PATCH] UML: Use PTRACE_KILL instead of SIGKILL to kill host-OS processes (take #2))

[Daniel Jacobowitz <dan@debian.org>]

On Thu, Nov 04, 2004 at 05:31:21AM +0100, Blaisorblade wrote:
> 2) getpid() on a child clone returns the process's pid when run with a 
> NPTL-enabled glibc, while it returns the thread pid with a LinuxThreads one; 
> this causes tons of problems with UML, which uses signals as inter-thread and 
> intra-thread communication.
> 
> Note UML is not using pthread_create() to create the threads, where this 
> behaviour is an improvement. I'm using a plain clone() call without the 
> CLONE_THREAD flag (which is not even added in by glibc, according to strace).
> 
> I've not yet checked if glibc is hijacking getpid() or not, but that would be 
> strange anyway.

Glibc caches the PID.  If you're going to use clone directly, use the
gettid/getpid syscall directly.  It's kind of rude that glibc breaks
getpid in this way; I recommend filing a bug in the glibc bugzilla at
sources.redhat.com.

-- 
Daniel Jacobowitz