xtensa: fix _Unwind_GetCFA

Returning context->cfa in _Unwind_GetCFA makes CFA point one stack frame
higher than what was actually used by code at context->ra. This results
in invalid CFA value in signal frames and premature unwinding completion
in forced unwinding used by uClibc NPTL thread cancellation.
Returning context->sp from _Unwind_GetCFA makes all CFA values valid and
matching code that used them.

2015-08-18  Max Filippov  <jcmvbkbc@gmail.com>
libgcc/
	* config/xtensa/unwind-dw2-xtensa.c (_Unwind_GetCFA): Return
	context->sp instead of context->cfa.

From-SVN: r226964

libgcc/ChangeLog

 2015-08-18  Max Filippov  <jcmvbkbc@gmail.com>
 
+	* config/xtensa/unwind-dw2-xtensa.c (_Unwind_GetCFA): Return
+	context->sp instead of context->cfa.
+
+2015-08-18  Max Filippov  <jcmvbkbc@gmail.com>
+
 	* config/xtensa/t-windowed (LIB2ADDEH): Replace unwind-dw2-fde
 	with unwind-dw2-fde-dip.
 

libgcc/config/xtensa/unwind-dw2-xtensa.c

@@ -130,7 +130,7 @@ _Unwind_GetGR (struct _Unwind_Context *context, int index)
 _Unwind_Word
 _Unwind_GetCFA (struct _Unwind_Context *context)
 {
-  return (_Unwind_Ptr) context->cfa;
+  return (_Unwind_Ptr) context->sp;
 }
 
 /* Overwrite the saved value for register INDEX in CONTEXT with VAL.  */