Use R0/R1 instead of R4/R5 for eh_return on ARM

gcc/unwind-pnacl.h

 #ifndef UNWIND_PNACL_H
 #define UNWIND_PNACL_H
 
 #define STACK_GROWS_DOWNWARD 1
 
 /* Define: __builtin_dwarf_sp_column */
 #if defined(__x86_64__)
 #define __builtin_dwarf_sp_column() 7
 #elif defined(__i386__)
 #define __builtin_dwarf_sp_column() 4
@@ skipping 76 matching lines @@
 #else
 #error "Unknown platform"
 #endif
 
 /* This corresponds to:  __builtin_eh_return_data_regno(0)  */
 #if defined(__x86_64__)
 #define pnacl_unwind_result0_reg() 0
 #elif defined(__i386__)
 #define pnacl_unwind_result0_reg() 0
 #elif defined(__arm__)
-#define pnacl_unwind_result0_reg() 4
+#define pnacl_unwind_result0_reg() 0
 #elif defined(__mips__)
 #define pnacl_unwind_result0_reg() 4
 #else

[jvoung (off chromium), 2015/06/03 17:21:04]

I wonder if mips is going to have the same problem...

[Derek Schuff, 2015/06/03 20:51:11]

Yeah, it seems likely. I still have the suspicion that there was something that
was kind of mitigating this problem before, that maybe isn't working now.
Because those registers were always getting clobbered before, and it seems kind
of inconceivable that there were never any situations where they were being used
until now.

 #error "unknown platform"
 #endif
 
 /* This corresponds to:   __builtin_eh_return_data_regno(1) */
 #if defined(__x86_64__)
 #define pnacl_unwind_result1_reg() 1
 #elif defined(__i386__)
 #define pnacl_unwind_result1_reg() 2
 #elif defined(__arm__)
-#define pnacl_unwind_result1_reg() 5
+#define pnacl_unwind_result1_reg() 1
 #elif defined(__mips__)
 #define pnacl_unwind_result1_reg() 5
 #else
 #error "unknown platform"
 #endif
 
 #endif /* UNWIND_PNACL_H */