[PATCH] D54154: [ELF][MIPS] Use MIPS R6 `sigrie` as a trap instruction

[James Clarke via Phabricator via llvm-commits]

jrtc27 added inline comments.


================
Comment at: ELF/Arch/Mips.cpp:61
+  // Set `sigrie 1` as a trap instruction.
+  if (Config->IsLE == sys::IsLittleEndianHost)
+    write32le(&TrapInstr, 0x04170001);
----------------
atanasyan wrote:
> jrtc27 wrote:
> > Maybe I'm being stupid, but won't this do the wrong thing on a big-endian host? If, say, we're building for mips64 on mips64, `Config->IsLE` and `sys::IsLittleEndianHost` will both be false, so we'll take the `write32le` path, which will write `0x04170001` (represented in-memory natively as big-endian) as a little-endian value, i.e. incorrectly byte-swapping? It seems to me like this should be just a check for `if (Config->IsLE)`?
> Thanks a lot. The only remaining question - how could I write this nice piece of code? :)
I went and verified this because, despite having many dealings with it, it's too easy to get confused about endianness-related code. So, yes, my belief was correct, and I didn't inadvertently mislead you :) Running on powerpc64-linux-gnu:

```
-- Testing: 1 tests, 1 threads --
FAIL: lld :: ELF/mips-got16-relocatable.s (1 of 1)
******************** TEST 'lld :: ELF/mips-got16-relocatable.s' FAILED ********************
Script:
--
: 'RUN: at line 5';   /home/jrtc27/src/llvm/Build/bin/llvm-mc -filetype=obj -triple=mips-unknown-linux -mcpu=mips32r6 -o /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp.o /home/jrtc27/src/llvm/llvm/tools/lld/test/ELF/mips-got16-relocatable.s
: 'RUN: at line 6';   /home/jrtc27/src/llvm/Build/bin/ld.lld -r -o /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp.o /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp.o
: 'RUN: at line 7';   /home/jrtc27/src/llvm/Build/bin/llvm-objdump -d -r /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp | /home/jrtc27/src/llvm/Build/bin/FileCheck -check-prefix=OBJ /home/jrtc27/src/llvm/llvm/tools/lld/test/ELF/mips-got16-relocatable.s
: 'RUN: at line 8';   /home/jrtc27/src/llvm/Build/bin/ld.lld -shared -o /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp.so /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp
: 'RUN: at line 9';   /home/jrtc27/src/llvm/Build/bin/llvm-objdump -d /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp.so | /home/jrtc27/src/llvm/Build/bin/FileCheck -check-prefix=SO /home/jrtc27/src/llvm/llvm/tools/lld/test/ELF/mips-got16-relocatable.s
--
Exit Code: 1

Command Output (stderr):
--
/home/jrtc27/src/llvm/llvm/tools/lld/test/ELF/mips-got16-relocatable.s:17:13: error: OBJ-NEXT: expected string not found in input
# OBJ-NEXT: 8: 04 17 00 01 sigrie 1
            ^
<stdin>:10:2: note: scanning from here
 8: 01 00 17 04 <unknown>
 ^

--

********************
Testing Time: 0.22s
********************
Failing Tests (1):
    lld :: ELF/mips-got16-relocatable.s

  Unexpected Failures: 1
```


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D54154