libunwind: Fix unw_getcontext() return value on AArch64.

[logan]

Summary

unw_getcontext() should return UNW_ESUCCESS on success. However, the assembly
for AArch64 is incorrect since "ldr x0, #0" is a PC-relative load instead of an
immediate value load.

This patch should fix the problem by changing ldr to mov.

[kledzik]

LGTM

[rengolin]

Ouch! LGTM. Thanks!

[logan]

Hi,

Thanks for your review. Committed as rL240648.

src/UnwindRegistersSave.S

DEFINE_LIBUNWIND_FUNCTION(unw_getcontext)
   stp    d18,d19, [x0, #0x1A0]
   stp    d20,d21, [x0, #0x1B0]
   stp    d22,d23, [x0, #0x1C0]
   stp    d24,d25, [x0, #0x1D0]
   stp    d26,d27, [x0, #0x1E0]
   stp    d28,d29, [x0, #0x1F0]
   str    d30,     [x0, #0x200]
   str    d31,     [x0, #0x208]
-  ldr    x0, #0                   // return UNW_ESUCCESS
+  mov    x0, #0                   // return UNW_ESUCCESS
   ret
 
 #elif defined(__arm__) && !defined(__APPLE__)
 
 #if !defined(__ARM_ARCH_ISA_ARM)
   .thumb
 #endif
 

test/unw_getcontext.pass.cpp

+#include <assert.h>
+#include <libunwind.h>
+
+int main() {
+  unw_context_t context;
+  int ret = unw_getcontext(&context);
+  assert(ret == UNW_ESUCCESS);
+}