[PATCH] [lbc++abi] [unwinder] Support Cortex-m0

[Renato Golin]

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Comment at: src/Unwind/UnwindRegistersRestore.S:341
@@ -330,1 +340,3 @@
+#endif
+#if __ARM_ARCH > 4 || __ARM_ARCH_4T__
   bx lr
----------------
I think we should use the same trick we used in other ARM files, to define a macro that is set by the arch for returning.

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Comment at: src/Unwind/UnwindRegistersRestore.S:355
@@ -342,2 +354,3 @@
 DEFINE_LIBUNWIND_PRIVATE_FUNCTION(_ZN9libunwind13Registers_arm19restoreVFPWithFLDMDEPy)
+#if !defined(__ARM_ARCH_6M__) && !defined(__ARM_ARCH_6SM__)
   @ VFP and iwMMX instructions are only available when compiling with the flags
----------------
Do you want to export the symbols (unwindVFP) but have it do nothing? Is it even possible to try to unwind VFP on v6M? Shouldn't this be a compilation error?

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Comment at: src/Unwind/UnwindRegistersRestore.S:380
@@ -365,2 +379,3 @@
 #if __ARM_ARCH < 7
+#if !defined(__ARM_ARCH_6M__) && !defined(__ARM_ARCH_6SM__)
   ldc p11, cr0, [r0], {0x21}  @ fldmiax r0, {d0-d15}
----------------
This macro is in a different order than the one above, and will generate vldmia on v6M which will fail.

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Comment at: src/Unwind/UnwindRegistersSave.S:285
@@ -284,1 +284,3 @@
 
+#if defined(__ARM_ARCH_6M__) || defined(__ARM_ARCH_6SM__) 
+  .thumb
----------------
Maybe we should also have a macro that will use thumb on thumb-only platforms like v6M and v6M variants. That would have to be accompanied by changes to other areas, making them Thumb/2 friendly (like the ones you add here).

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Comment at: src/Unwind/UnwindRegistersSave.S:368
@@ -350,2 +367,3 @@
 DEFINE_LIBUNWIND_PRIVATE_FUNCTION(_ZN9libunwind13Registers_arm9saveVFPv3EPy)
+#if defined(__ARM_ARCH_6M__) || defined(__ARM_ARCH_6SM__) 
   @ VFP and iwMMX instructions are only available when compiling with the flags
----------------
compnerd wrote:
> This also doesn't work for ARMv7.  Consider ARM VFPv3-d16 (e.g. Tegra2) ... vstmia r0, {d16-d31} refers to a non-existent register set.
And this is exactly the opposite as the other, which would just get "bx lr" on ARMv6M

http://reviews.llvm.org/D5314