On Sat, Dec 08, 2007 at 08:24:57PM -0800, John Reiser wrote:
>In source file arch/um/os-Linux/process.c there is a warning:
>-----
>/* Don't use the glibc version, which caches the result in TLS. It misses some
> * syscalls, and also breaks with clone(), which does not unshare the TLS.
> */
>
>int os_getpid(void)
AFAIK, there are two reasons that we make sure we call the system call
getpid -
when we're testing ptrace, we want getpid to result in exactly
one system call
there was a brief bug in libc where getpid returned the wrong
answer due to caching across a clone
This bug did get into the wild, and people did try to run UML on such
systems, so that's why the code is careful about making the system call.
> I see no os_clone(), yet the glibc clone() does the same caching of pid in
> ThreadLocalStorage [TLS], and the TLS still may be shared. If nobody reads
> glibc's shared TLS slot for PID then an actual bug will be avoided. However,
> it is unsafe to leave such a tempting pitfall.
What's the actual bug, exactly? As long as libc's getpid gives us the
right answer, we're happy.
> Also, if you are ptrace()ing
> through a glibc clone(), then in many cases you will see syscall(__NR_getpid)
> *from glibc* immediately following! There is an "extra" getpid()
> that the tracking logic might not expect.
Where do we care about how clone translates into a system call?
> arch/um/drivers/ubd_user.c
> arch/um/kernel/tt/tracer.c
> arch/um/os/tt.c
> arch/um/os/start_up.c
> arch/um/os/skas/process.c
These guys all just want a new process - they don't care how it
happens.
Is something in here causing valgrind some trouble?
Jeff
--
Work email - jdike at linux dot intel dot com
-------------------------------------------------------------------------
SF.Net email is sponsored by:
Check out the new SourceForge.net Marketplace.
It's the best place to buy or sell services for
just about anything Open Source.
http://sourceforge.net/services/buy/index.php
_______________________________________________
User-mode-linux-devel mailing list
User-mode-linux-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
