[lld] Add support for relocations in x86_64 objects on Arm64EC targets.

[jacek]

Summary

Since EC targets may combine various object types, we need to pick relocation format based on chunk type instead of global config.

[jacek]

Moving to https://github.com/llvm/llvm-project/pull/69098

lld/COFF/Chunks.h

public:
   };
 
   SectionChunk(ObjFile *file, const coff_section *header);
   static bool classof(const Chunk *c) { return c->kind() == SectionKind; }
   size_t getSize() const { return header->SizeOfRawData; }
   ArrayRef<uint8_t> getContents() const;
   void writeTo(uint8_t *buf) const;
 
+  MachineTypes getMachine() const { return file->getMachineType(); }
+
   // Defend against unsorted relocations. This may be overly conservative.
   void sortRelocations();
 
   // Write and relocate a portion of the section. This is intended to be called
   // in a loop. Relocations must be sorted first.
   void writeAndRelocateSubsection(ArrayRef<uint8_t> sec,
                                   ArrayRef<uint8_t> subsec,
                                   uint32_t &nextRelocIndex, uint8_t *buf) const;

lld/COFF/Chunks.cpp

if (!sym ||
     return;
   }
 
   uint64_t s = sym->getRVA();
 
   // Compute the RVA of the relocation for relative relocations.
   uint64_t p = rva + rel.VirtualAddress;
   uint64_t imageBase = file->ctx.config.imageBase;
-  switch (file->ctx.config.machine) {
+  switch (getMachine()) {
   case AMD64:
     applyRelX64(off, rel.Type, os, s, p, imageBase);
     break;
   case I386:
     applyRelX86(off, rel.Type, os, s, p, imageBase);
     break;
   case ARMNT:
     applyRelARM(off, rel.Type, os, s, p, imageBase);

 }
 
 // Windows-specific.
 // Collect all locations that contain absolute addresses, which need to be
 // fixed by the loader if load-time relocation is needed.
 // Only called when base relocation is enabled.
 void SectionChunk::getBaserels(std::vector<Baserel> *res) {
   for (const coff_relocation &rel : getRelocs()) {
-    uint8_t ty = getBaserelType(rel, file->ctx.config.machine);
+    uint8_t ty = getBaserelType(rel, getMachine());
     if (ty == IMAGE_REL_BASED_ABSOLUTE)
       continue;
     Symbol *target = file->getSymbol(rel.SymbolTableIndex);
     if (!target || isa<DefinedAbsolute>(target))
       continue;
     res->emplace_back(rva + rel.VirtualAddress, ty);
   }
 }

lld/test/COFF/arm64ec-reloc.test

+REQUIRES: aarch64, x86
+RUN: split-file %s %t.dir && cd %t.dir
+
+Link a mix of ARM64EC and x86_64 data and check that relocations work.
+
+RUN: llvm-mc -filetype=obj -triple=arm64ec-windows arm64ec-data-sym.s -o arm64ec-data-sym.obj
+RUN: llvm-mc -filetype=obj -triple=x86_64-windows x86_64-data-sym.s -o x86_64-data-sym.obj
+RUN: lld-link -out:test.dll -machine:arm64ec arm64ec-data-sym.obj x86_64-data-sym.obj -dll -noentry
+
+RUN: llvm-readobj --hex-dump=.data test.dll | FileCheck -check-prefix=ARM64EC-DATA %s
+ARM64EC-DATA: 0x180001000 00100080 01000000 08100080 01000000
+
+RUN: llvm-readobj --coff-basereloc test.dll | FileCheck -check-prefix=RELOCS %s
+RELOCS:      BaseReloc [
+RELOCS-NEXT:   Entry {
+RELOCS-NEXT:     Type: DIR64
+RELOCS-NEXT:     Address: 0x1000
+RELOCS-NEXT:   }
+RELOCS-NEXT:   Entry {
+RELOCS-NEXT:     Type: DIR64
+RELOCS-NEXT:     Address: 0x1008
+RELOCS-NEXT:   }
+RELOCS-NEXT: ]
+
+#--- arm64ec-data-sym.s
+        .data
+        .globl arm64ec_data_sym
+        .p2align 2, 0x0
+arm64ec_data_sym:
+        .xword arm64ec_data_sym
+
+#--- x86_64-data-sym.s
+        .data
+        .globl x86_64_data_sym
+        .p2align 2, 0x0
+x86_64_data_sym:
+        .quad x86_64_data_sym