Fix ARM fpu_control.h for assemblers requiring VFP insn names (bug 21047) [committed]

[Joseph Myers <joseph at codesourcery dot com>]

Bug 21047 reports that the clang assembler disallows the ARM
implementations of _FPU_GETCW and _FPU_SETCW.

These are deliberately written the way they are, using generic
coprocessor instructions (from the days when VFP was just one possible
coprocessor for ARM) that have the right encodings, to handle the case
of the instructions being used runtime-conditionally inside glibc,
where use of these macros is not meant to result in either the
assembler requiring VFP to be enabled at assembly time or in it
marking the object as using VFP.  However, more recent ARM ARM
versions have restricted the definitions of the coprocessor
instructions and reportedly the clang assembler follows that in
disallowing those names for VFP instructions.

In the non-__SOFTFP__ case - which in fact is the only case where
these macro definitions can be used outside the build of glibc itself
- using VFP instruction names is of course fine, since we know that
VFP is enabled for that compilation.  Thus, this patch uses the
current VFP names for these instructions in that case to improve
compatibility for this header file.

Tested for hard-float and soft-float builds of glibc, including that
installed stripped shared libraries are unchanged by the patch.  
Committed.

2017-01-19  Joseph Myers  <joseph@codesourcery.com>

	[BZ #21047]
	* sysdeps/arm/fpu_control.h [!__SOFTFP__] (_FPU_GETCW): Use VFP
	name for instruction.
	[!__SOFTFP__] (_FPU_SETCW): Likewise.

diff --git a/sysdeps/arm/fpu_control.h b/sysdeps/arm/fpu_control.h
index d49066c..405d427 100644
--- a/sysdeps/arm/fpu_control.h
+++ b/sysdeps/arm/fpu_control.h
@@ -53,12 +53,19 @@ extern fpu_control_t __fpu_control;
 typedef unsigned int fpu_control_t;
 
 /* Macros for accessing the hardware control word.  */
+#ifdef __SOFTFP__
 /* This is fmrx %0, fpscr.  */
-#define _FPU_GETCW(cw) \
+# define _FPU_GETCW(cw) \
   __asm__ __volatile__ ("mrc p10, 7, %0, cr1, cr0, 0" : "=r" (cw))
 /* This is fmxr fpscr, %0.  */
-#define _FPU_SETCW(cw) \
+# define _FPU_SETCW(cw) \
   __asm__ __volatile__ ("mcr p10, 7, %0, cr1, cr0, 0" : : "r" (cw))
+#else
+# define _FPU_GETCW(cw) \
+  __asm__ __volatile__ ("vmrs %0, fpscr" : "=r" (cw))
+# define _FPU_SETCW(cw) \
+  __asm__ __volatile__ ("vmsr fpscr, %0" : : "r" (cw))
+#endif
 
 /* Default control word set at startup.  */
 extern fpu_control_t __fpu_control;

-- 
Joseph S. Myers
joseph@codesourcery.com