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)
-----
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. 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. So it seems to me that
there should be an os_clone() that refrains from fiddling with getpid.
[Unfortunately os_clone() is not so simple as os_getpid().]
The clone() we're talking about here is _not_ the bare syscall:
-----
_syscall5(int, clone, int, flags, void *, child_stack,
int *, parent_tidptr, struct user_desc *, newtls,
int *, child_tidptr)
-----
but rather the C-language interface:
-----
int clone(int (*fn)(void *), void *child_stack,
int flags, void *arg, ...
/* pid_t *pid, struct user_desc *tls, pid_t *ctid */ );
-----
which is declared in arch/um/include/kern.h and referenced in
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
This clone() is implemented by glibc, and at runtime lives in the shared
library /lib/libc.so.6.
Not only that, but some versions of glibc for x86 use "int $0x80" directly
only for the __NR_clone call. They use "ENTER_KERNEL" for the getpid(),
which in some cases (such as Fedora 7 and 8, but not Ubuntu 7.04) expands to
"call *%gs:nnnnn" which points at "sysenter; ret".
--
John Reiser, [EMAIL PROTECTED]
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