[LLD][ELF] Make --fix-cortex-a53-843419 work on big endian hosts

[peter.smith]

Summary

The reinterpret cast to uint32_t to read the little-endian instructions will only work on a little endian system. Use ulittle32_t to always read little-endian (AArch64 instructions are always little endian).

Fixes PR36056: https://bugs.llvm.org/show_bug.cgi?id=36056

An alternative logically equivalent fix is to use read32le into a uint32_t but that is slightly more of a change to the structure of the code. I've uploaded to the PR a prototype fix under https://bugs.llvm.org/attachment.cgi?id=19727 and can use that if you prefer.

Found by Simon Dardis during release candidate testing on a Mips Big Endian system.

[peter.smith]

+ const ulittle32_t *InstBuf = reinterpret_cast<const ulittle32_t *>(Buf + Off);

This is OK.

+ ulittle32_t Instr1 = *InstBuf++;
+ ulittle32_t Instr2 = *InstBuf++;
+ ulittle32_t Instr3 = *InstBuf++;

But the values should still be uint32_t. The endian.h types should only
ever be used to form pointers.

Cheers,
Rafael

Thanks for pointing that out. I've updated the diff accordingly.

[peter.smith]

Spoke to soon, forgot to correct the last ulittle32_t that was hiding from me. Now updated.

lld/trunk/ELF/AArch64ErrataFix.cpp

 
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 
 using namespace llvm;
 using namespace llvm::ELF;
 using namespace llvm::object;
+using namespace llvm::support;
 using namespace llvm::support::endian;
 
 using namespace lld;
 using namespace lld::elf;
 
 // Helper functions to identify instructions and conditions needed to trigger
 // the Cortex-A53-843419 erratum.
 
static uint64_t scanCortexA53Errata843419(InputSection *IS, uint64_t &Off,
   if (Off >= Limit || Limit - Off < 12) {
     // Need at least 3 4-byte sized instructions to trigger erratum.
     Off = Limit;
     return 0;
   }
 
   uint64_t PatchOff = 0;
   const uint8_t *Buf = IS->Data.begin();
-  const uint32_t *InstBuf = reinterpret_cast<const uint32_t *>(Buf + Off);
+  const ulittle32_t *InstBuf = reinterpret_cast<const ulittle32_t *>(Buf + Off);
   uint32_t Instr1 = *InstBuf++;
   uint32_t Instr2 = *InstBuf++;
   uint32_t Instr3 = *InstBuf++;
   if (is843419ErratumSequence(Instr1, Instr2, Instr3)) {
     PatchOff = Off + 8;
   } else if (OptionalAllowed && !isBranch(Instr3)) {
     uint32_t Instr4 = *InstBuf++;
     if (is843419ErratumSequence(Instr1, Instr2, Instr4))