powerpc: setcontext.S uses power6 mtfsf when not supported [BZ #18116]

The attached patch fixes a glibc build failure with gcc 5 on powerpc64le
caused by a recent change in gcc where the compiler defines the
_ARCH_PWR6 macro when processing assembly files but doesn't invoke the
assembler in the corresponding machine mode (unless it has been
explicitly configured to target POWER 6 or later).  A bug had been filed
with gcc for this (65341) but was closed as won't fix. Glibc relies on
the _ARCH_PWR6 macro in a few .S files to make use of Power ISA 2.5
instructions (specifically, the four-argument form of the mtfsf insn).
A similar problem had occurred in the past (bug 10118) but the fix that
was committed for it didn't anticipate this new problem.

ChangeLog

@@ -1,3 +1,12 @@
+2015-03-11  Martin Sebor  <msebor@redhat.com>
+
+	[BZ #18116]
+        * sysdeps/unix/sysv/linux/powerpc/powerpc64/setcontext.S
+        (__setcontext): Use extended four-operand version of mtsf whenever
+	possible.
+        * sysdeps/unix/sysv/linux/powerpc/powerpc64/swapcontext.S
+        (__novec_swapcontext): Likewise.
+
 2015-06-01  Siddhesh Poyarekar  <siddhesh@redhat.com>
 
 	* benchtests/scripts/compare_bench.py: New file.

sysdeps/unix/sysv/linux/powerpc/powerpc64/setcontext.S

@@ -81,22 +81,31 @@ ENTRY(__novec_setcontext)
 
 # ifdef _ARCH_PWR6
   /* Use the extended four-operand version of the mtfsf insn.  */
-  mtfsf  0xff,fp0,1,0
-# else
   .machine push
   .machine "power6"
+
+  mtfsf  0xff,fp0,1,0
+
+  .machine pop
+# else
   /* Availability of DFP indicates a 64-bit FPSCR.  */
   andi.  r6,r5,PPC_FEATURE_HAS_DFP
   beq    5f
   /* Use the extended four-operand version of the mtfsf insn.  */
+  .machine push
+  .machine "power6"
+
   mtfsf  0xff,fp0,1,0
+
+  .machine pop
+
   b      6f
   /* Continue to operate on the FPSCR as if it were 32-bits.  */
 5:
   mtfsf  0xff,fp0
 6:
-  .machine pop
 # endif /* _ARCH_PWR6 */
+
   lfd  fp29,(SIGCONTEXT_FP_REGS+(PT_R29*8))(r31)
   lfd  fp28,(SIGCONTEXT_FP_REGS+(PT_R28*8))(r31)
   lfd  fp27,(SIGCONTEXT_FP_REGS+(PT_R27*8))(r31)
@@ -364,22 +373,31 @@ L(has_no_vec):
 
 # ifdef _ARCH_PWR6
   /* Use the extended four-operand version of the mtfsf insn.  */
-  mtfsf  0xff,fp0,1,0
-# else
   .machine push
   .machine "power6"
+
+  mtfsf  0xff,fp0,1,0
+
+  .machine pop
+# else
   /* Availability of DFP indicates a 64-bit FPSCR.  */
   andi.  r6,r5,PPC_FEATURE_HAS_DFP
   beq    7f
   /* Use the extended four-operand version of the mtfsf insn.  */
+  .machine push
+  .machine "power6"
+
   mtfsf  0xff,fp0,1,0
+
+  .machine pop
+
   b      8f
   /* Continue to operate on the FPSCR as if it were 32-bits.  */
 7:
   mtfsf  0xff,fp0
 8:
-  .machine pop
 # endif /* _ARCH_PWR6 */
+
   lfd  fp29,(SIGCONTEXT_FP_REGS+(PT_R29*8))(r31)
   lfd  fp28,(SIGCONTEXT_FP_REGS+(PT_R28*8))(r31)
   lfd  fp27,(SIGCONTEXT_FP_REGS+(PT_R27*8))(r31)

sysdeps/unix/sysv/linux/powerpc/powerpc64/swapcontext.S

@@ -173,24 +173,34 @@ ENTRY(__novec_swapcontext)
   lfd  fp0,(SIGCONTEXT_FP_REGS+(32*8))(r31)
   lfd  fp31,(SIGCONTEXT_FP_REGS+(PT_R31*8))(r31)
   lfd  fp30,(SIGCONTEXT_FP_REGS+(PT_R30*8))(r31)
+
 # ifdef _ARCH_PWR6
   /* Use the extended four-operand version of the mtfsf insn.  */
-  mtfsf  0xff,fp0,1,0
-# else
   .machine push
   .machine "power6"
+
+  mtfsf  0xff,fp0,1,0
+
+  .machine pop
+# else
   /* Availability of DFP indicates a 64-bit FPSCR.  */
   andi.  r6,r8,PPC_FEATURE_HAS_DFP
   beq    5f
-  /* Use the extended four-operand version of the mtfsf insn.  */
+
+  .machine push
+  .machine "power6"
+
   mtfsf  0xff,fp0,1,0
+
+  .machine pop
+
   b      6f
   /* Continue to operate on the FPSCR as if it were 32-bits.  */
 5:
   mtfsf  0xff,fp0
 6:
-  .machine pop
 #endif /* _ARCH_PWR6 */
+
   lfd  fp29,(SIGCONTEXT_FP_REGS+(PT_R29*8))(r31)
   lfd  fp28,(SIGCONTEXT_FP_REGS+(PT_R28*8))(r31)
   lfd  fp27,(SIGCONTEXT_FP_REGS+(PT_R27*8))(r31)
@@ -652,24 +662,34 @@ L(has_no_vec2):
   lfd  fp0,(SIGCONTEXT_FP_REGS+(32*8))(r31)
   lfd  fp31,(SIGCONTEXT_FP_REGS+(PT_R31*8))(r31)
   lfd  fp30,(SIGCONTEXT_FP_REGS+(PT_R30*8))(r31)
+
 # ifdef _ARCH_PWR6
   /* Use the extended four-operand version of the mtfsf insn.  */
-  mtfsf  0xff,fp0,1,0
-# else
   .machine push
   .machine "power6"
+
+  mtfsf  0xff,fp0,1,0
+
+  .machine pop
+# else
   /* Availability of DFP indicates a 64-bit FPSCR.  */
   andi.  r6,r8,PPC_FEATURE_HAS_DFP
   beq    7f
-  /* Use the extended four-operand version of the mtfsf insn.  */
+
+  .machine push
+  .machine "power6"
+
   mtfsf  0xff,fp0,1,0
+
+  .machine pop
+
   b      8f
   /* Continue to operate on the FPSCR as if it were 32-bits.  */
 7:
   mtfsf  0xff,fp0
 8:
-  .machine pop
 #endif /* _ARCH_PWR6 */
+
   lfd  fp29,(SIGCONTEXT_FP_REGS+(PT_R29*8))(r31)
   lfd  fp28,(SIGCONTEXT_FP_REGS+(PT_R28*8))(r31)
   lfd  fp27,(SIGCONTEXT_FP_REGS+(PT_R27*8))(r31)