[lld] [lld][macho] Support 1-byte branch relocs for x86_64 (PR #164439)

[Jez Ng via llvm-commits]

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@@ -84,6 +84,8 @@ int64_t X86_64::getEmbeddedAddend(MemoryBufferRef mb, uint64_t offset,
   const uint8_t *loc = buf + offset + rel.r_address;
 
   switch (rel.r_length) {
+  case 0:
+    return *loc + pcrelOffset(rel.r_type);
   case 2:
     return static_cast<int32_t>(read32le(loc)) + pcrelOffset(rel.r_type);
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int3 wrote:

the static cast here is correct. `read32le` returns an unsigned int32_t but addends can be negative, so we need to cast to int32_t to handle them correctly.

> Does it make sense to factor this out by adding a new address variable and return address + pcrelOffset(rel.r_type); at the end?

sure, done

https://github.com/llvm/llvm-project/pull/164439