Re: [PATCH][BZ #16214] Fix TLS access on S390 with -march=z10

[Andreas Krebbel <krebbel at linux dot vnet dot ibm dot com>]

On Thu, Nov 28, 2013 at 05:53:10PM +0530, Siddhesh Poyarekar wrote:
> How about just something like:
> 
> strong_alias (__tls_get_addr, __tls_get_addr_internal);
> 
> and then adding __tls_get_addr_internal as GLIBC_PRIVATE in Versions?
> I believe that should keep __tls_get_addr private and export
> __tls_get_addr_internal@@GLIBC_PRIVATE.  I don't have a test box yet
> to verify my claim, so this is again a suggestion based on just
> reading the code.

You are right it is really that simple.  An alias removes the hidden
attribute.

Attached is an updated version of the patch addressing your comments.

Bye,

-Andreas-


2013-11-28  Siddhesh Poyarekar  <siddhesh@redhat.com>
	    Andreas Krebbel  <Andreas.Krebbel@de.ibm.com>

	[BZ #16214]
	* sysdeps/s390/dl-tls.h (__TLS_GET_ADDR): Invoke
	__tls_get_addr_internal instead of __tls_get_offset in order to
	avoid GOT pointer dependency.  Make rtld export
	__tls_get_addr_internal@@GLIBC_PRIVATE while still hiding
	__tls_get_addr since we are a __tls_get_offset platform.
	* sysdeps/s390/s390-64/tls-macros.h (TLS_IE PIC): Don't rely on
	GOT pointer being set up before.
	* sysdeps/s390/s390-32/tls-macros.h (TLS_IE PIC): Likewise.


commit e648fd8cb80f6ee97730cae5133250a38146dd1d
Author: Andreas Krebbel <krebbel@linux.vnet.ibm.com>
Date:   Wed Nov 27 18:17:09 2013 +0100

    [BZ #16214] S/390: Fix TLS GOT pointer setup.

diff --git a/sysdeps/s390/Versions b/sysdeps/s390/Versions
index e18617c..baf9842 100644
--- a/sysdeps/s390/Versions
+++ b/sysdeps/s390/Versions
@@ -3,4 +3,8 @@ ld {
     # runtime interface to TLS
     __tls_get_offset;
   }
+  GLIBC_PRIVATE {
+    # Exported by ld used by libc.
+    __tls_get_addr_internal;
+  }
 }
diff --git a/sysdeps/s390/dl-tls.h b/sysdeps/s390/dl-tls.h
index 68a5af4..3eb1c6b 100644
--- a/sysdeps/s390/dl-tls.h
+++ b/sysdeps/s390/dl-tls.h
@@ -26,11 +26,21 @@ typedef struct
 
 
 #ifdef SHARED
-/* This is the prototype for the GNU version.  */
-extern void *__tls_get_addr (tls_index *ti) attribute_hidden;
+
 extern unsigned long __tls_get_offset (unsigned long got_offset);
 
 # ifdef IS_IN_rtld
+
+#  include <shlib-compat.h>
+
+extern void *__tls_get_addr (tls_index *ti) attribute_hidden;
+/* Make an temporary alias to get rid of the hidden attribute.  The
+   hidden attribute is required to prevent __tls_get_addr from being
+   exported.  */
+strong_alias (__tls_get_addr, __tls_get_addr_internal1);
+versioned_symbol (ld, __tls_get_addr_internal1,
+		  __tls_get_addr_internal, GLIBC_PRIVATE);
+
 /* The special thing about the s390 TLS ABI is that we do not have the
    standard __tls_get_addr function but the __tls_get_offset function
    which differs in two important aspects:
@@ -63,15 +73,21 @@ __tls_get_offset:\n\
 1:	.long	__tls_get_addr - 0b\n\
 ");
 #  endif
-# endif
+# else /* IS_IN_rtld */
+extern void *__tls_get_addr_internal (tls_index *ti);
+# endif /* !IS_IN_rtld */
 
 # define GET_ADDR_OFFSET \
   (ti->ti_offset - (unsigned long) __builtin_thread_pointer ())
 
-# define __TLS_GET_ADDR(__ti) \
-  ({ extern char _GLOBAL_OFFSET_TABLE_[] attribute_hidden;		  \
-     (void *) __tls_get_offset ((char *) (__ti) - _GLOBAL_OFFSET_TABLE_)  \
-     + (unsigned long) __builtin_thread_pointer (); })
+/* Use the privately exported __tls_get_addr_internal instead of
+   __tls_get_offset in order to avoid the __tls_get_offset special
+   linkage requiring the GOT pointer to be set up in r12.  The
+   compiler will take care of setting up r12 only if itself issued the
+   __tls_get_offset call.  */
+# define __TLS_GET_ADDR(__ti)					\
+  ({ (void *) __tls_get_addr_internal ((char *) (__ti))		\
+      + (unsigned long) __builtin_thread_pointer (); })
 
 #endif
 
diff --git a/sysdeps/s390/s390-32/tls-macros.h b/sysdeps/s390/s390-32/tls-macros.h
index 8a0ad58..a592d81 100644
--- a/sysdeps/s390/s390-32/tls-macros.h
+++ b/sysdeps/s390/s390-32/tls-macros.h
@@ -8,12 +8,15 @@
 
 #ifdef PIC
 # define TLS_IE(x) \
-  ({ unsigned long __offset;						      \
+  ({ unsigned long __offset, __got;					      \
      asm ("bras %0,1f\n"						      \
-	  "0:\t.long " #x "@gotntpoff\n"				      \
-	  "1:\tl %0,0(%0)\n\t"						      \
-	  "l %0,0(%0,%%r12):tls_load:" #x				      \
-	  : "=&a" (__offset) : : "cc" );				      \
+	  "0:\t.long _GLOBAL_OFFSET_TABLE_-0b\n\t"			      \
+	  ".long " #x "@gotntpoff\n"					      \
+	  "1:\tl %1,0(%0)\n\t"						      \
+	  "la %1,0(%1,%0)\n\t"						      \
+	  "l %0,4(%0)\n\t"						      \
+	  "l %0,0(%0,%1):tls_load:" #x "\n"				      \
+	  : "=&a" (__offset), "=&a" (__got) : : "cc" );			      \
      (int *) (__builtin_thread_pointer() + __offset); })
 #else
 # define TLS_IE(x) \
diff --git a/sysdeps/s390/s390-64/tls-macros.h b/sysdeps/s390/s390-64/tls-macros.h
index be8aa6c..3c59436 100644
--- a/sysdeps/s390/s390-64/tls-macros.h
+++ b/sysdeps/s390/s390-64/tls-macros.h
@@ -8,12 +8,13 @@
 
 #ifdef PIC
 # define TLS_IE(x) \
-  ({ unsigned long __offset;						      \
-     asm ("bras %0,1f\n"						      \
-	  "0:\t.quad " #x "@gotntpoff\n"				      \
-	  "1:\tlg %0,0(%0)\n\t"						      \
-	  "lg %0,0(%0,%%r12):tls_load:" #x				      \
-	  : "=&a" (__offset) : : "cc" );				      \
+  ({ unsigned long __offset, __got;					      \
+     asm ("bras %0,0f\n\t"						      \
+	  ".quad " #x "@gotntpoff\n"					      \
+	  "0:\tlarl %1,_GLOBAL_OFFSET_TABLE_\n\t"			      \
+	  "lg %0,0(%0)\n\t"						      \
+	  "lg %0,0(%0,%1):tls_load:" #x	"\n"				      \
+	  : "=&a" (__offset), "=&a" (__got) : : "cc" );			      \
      (int *) (__builtin_thread_pointer() + __offset); })
 #else
 # define TLS_IE(x) \