[libcxx-commits] [PATCH] D128998: [libunwind] Handle G in personality string

[Youngsuk Kim via Phabricator via libcxx-commits]

JOE1994 added inline comments.


================
Comment at: libunwind/src/DwarfInstructions.hpp:225
+          __asm__ __volatile__(".arch_extension memtag\n"
+                               "stg %[Ptr], [%[Ptr]]\n"
+                               :
----------------
This added inline assembly (`stg` instruction).
According to [the ARM instruction reference guide](https://developer.arm.com/documentation/100076/0100/fou1538563923467), `stg` instruction is only supported in `ARMv8.5` and later.

Since this change (D128998), I can no longer build `libunwind` on my `ARMv8.1` machine.
The assembler gives the following error:

```
/tmp/ccim5Evd.s: Assembler messages:
/tmp/ccim5Evd.s:9031: Error: unknown architectural extension `memtag'
/tmp/ccim5Evd.s:9031: Error: unknown mnemonic `stg' -- `stg x2,[x2]'
/tmp/ccim5Evd.s:9040: Error: unknown architectural extension `memtag'
/tmp/ccim5Evd.s:9040: Error: unknown mnemonic `stg' -- `stg x2,[x2]'
```

Is there a way to add a guard to only insert the `stg` instruction in supported ISAs?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D128998/new/

https://reviews.llvm.org/D128998