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

From: Daniel Jacobowitz
Date: Thu Nov 11 2004 - 13:03:40 EST

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

Daniel Jacobowitz
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