Hi All,

This patch fixes an issue reported by one of our customers where an instruction
exception gets raised when using '__sync_fetch_and_add' on a PowerPC 440
processor.  The instruction causing the exception is 'lwsync'.  Luckily Joseph
laid the groundwork when solving a similar issue for e500 cores [1] by adding a
new macro ('TARGET_NO_LWSYNC') for controlling whether 'lwsync' is available .

This patch extends the 'TARGET_NO_LWSYNC' macro to include the PowerPC 440
and 603 processors.  The 440 because that is what the problem was reported
against and the 603 because problems have been reported elsewhere [4] about
that.  It doesn't seem like 'lwsync' is supported on 603 processors anyway.  I
looked at the IBM [2] and Freescale [3] manuals and both use the heavyweight
implementation of 'sync' (i.e. the 'sync' bit L=0).

FWIW, I also took a look at the Linux kernel code and 'lwsync' is only used
on 64-bit PowerPC processors and e500 processors that can support it.  This
can be seen in 'arch/powerpc/include/asm/synch.h':

   #if defined(__powerpc64__)
   #    define LWSYNC   lwsync
   #elif defined(CONFIG_E500)
   #    define LWSYNC                                   \
        START_LWSYNC_SECTION(96);                       \
        sync;                                           \
        MAKE_LWSYNC_SECTION_ENTRY(96, __lwsync_fixup);
   #    define LWSYNC   sync

Support for the e500 processors is determined at runtime and the kernel is
dynamically patched.

Regression tested with powerpc-none-eabi.


P.S.  If it is OK can some please commit for me?  I don't have write access.

[1] http://gcc.gnu.org/ml/gcc-patches/2006-11/msg01238.html
[3] http://cache.freescale.com/files/32bit/doc/ref_manual/MPC603EUM.pdf
[4] http://gcc.gnu.org/ml/gcc/2008-06/msg00449.html

Meador Inge
CodeSourcery / Mentor Embedded
2012-03-27  Meador Inge  <mead...@codesourcery.com>

	* config/rs6000/rs6000.h (TARGET_NO_LWSYNC): Extended to cover PPC
	440 and 603 processors.
Index: gcc/config/rs6000/rs6000.h
--- gcc/config/rs6000/rs6000.h	(revision 185881)
+++ gcc/config/rs6000/rs6000.h	(working copy)
@@ -501,8 +501,10 @@ extern int rs6000_vector_align[];
-/* E500 processors only support plain "sync", not lwsync.  */
+/* Some processors only support plain "sync", not lwsync.  */
+			  || rs6000_cpu == PROCESSOR_PPC440 \
+			  || rs6000_cpu == PROCESSOR_PPC603)
 /* Which machine supports the various reciprocal estimate instructions.  */

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