[PATCH] s390: tls pointer extraction in __libc_start_main

[Martin Schwidefsky <schwidefsky at de dot ibm dot com>]

Greetings,
a glibc compiled with the latest gcc crashes in __libc_start_main.
The cause is that the compiler has decided to extract the tls pointer
in __libc_start_main() from the access registers a0/a1 into a general
register before the tls pointer has been set up by the call to
__pthread_initialize_minimal(). 

The least invasive fix is to clobber the access registers before the
first use in THREAD_SET_STACK_GUARD(). This makes the compiler to
do the tls pointer extraction after __pthread_initialize_minimal().

-- 
blue skies,
  Martin.

"Reality continues to ruin my life." - Calvin.
--

2008-10-06  Martin Schwidefsky  <schwidefsky@de.ibm.com>

	* sysdeps/s390/tls.h (THREAD_SET_STACK_GUARD): Add empty inline
	assembly with a clobber list for access registers a0 and a1.

diff -urpN libc/nptl/sysdeps/s390/tls.h libc-s390/nptl/sysdeps/s390/tls.h
--- libc/nptl/sysdeps/s390/tls.h	2007-08-07 13:09:01.000000000 +0200
+++ libc-s390/nptl/sysdeps/s390/tls.h	2008-10-06 19:55:46.000000000 +0200
@@ -161,7 +161,12 @@ typedef struct
 
 /* Set the stack guard field in TCB head.  */
 #define THREAD_SET_STACK_GUARD(value) \
-  THREAD_SETMEM (THREAD_SELF, header.stack_guard, value)
+  do 									      \
+   {									      \
+     __asm __volatile ("" : : : "a0", "a1");				      \
+     THREAD_SETMEM (THREAD_SELF, header.stack_guard, value);		      \
+   }									      \
+  while (0)
 #define THREAD_COPY_STACK_GUARD(descr) \
   ((descr)->header.stack_guard						      \
    = THREAD_GETMEM (THREAD_SELF, header.stack_guard))