[lld] [LLD][COFF] Add basic ARM64X dynamic relocations support (PR #118035)

[Martin Storsjö via llvm-commits]

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@@ -2555,6 +2566,33 @@ void Writer::addBaserelBlocks(std::vector<Baserel> &v) {
   relocSec->addChunk(make<BaserelChunk>(page, &v[i], &v[0] + j));
 }
 
+void Writer::createDynamicRelocs() {
+  if (!ctx.dynamicRelocs)
+    return;
+
+  const uint32_t coffHeaderOffset = dosStubSize + sizeof(PEMagic);
+  const uint32_t peHeaderOffset = coffHeaderOffset + sizeof(coff_file_header);
+  const uint32_t dataDirOffset = peHeaderOffset + sizeof(pe32plus_header);
+
+  // Adjust the Machine field in the COFF header to AMD64.
+  ctx.dynamicRelocs->add(IMAGE_DVRT_ARM64X_FIXUP_TYPE_VALUE, sizeof(uint16_t),
+                         coffHeaderOffset + offsetof(coff_file_header, Machine),
+                         AMD64);
+
+  // Adjust the load config directory.
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mstorsjo wrote:

"Adjust", as in setting the values to 0, if I understand the code correctly? Can you adjust (no pun intended ;-) ) the comment to be more clear about what adjustment it does?

Then again, I guess that the FIXME below means that clearing it isn't the final intended behaviour, but an initial stepping stone?

https://github.com/llvm/llvm-project/pull/118035