[clang] [llvm] [MC,llvm-readobj,yaml2obj] Support CREL relocation format (PR #91280)

[Peter Smith via llvm-commits]

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@@ -1278,29 +1285,69 @@ void ELFState<ELFT>::writeSectionContent(
   if (!Section.Relocations)
     return;
 
+  const bool IsCrel = Section.Type == llvm::ELF::SHT_CREL;
   const bool IsRela = Section.Type == llvm::ELF::SHT_RELA;
+  typename ELFT::uint OffsetMask = 8, Offset = 0, Addend = 0;
+  uint32_t Symidx = 0, Type = 0;
+  uint64_t CurrentOffset = CBA.getOffset();
+  if (IsCrel)
+    for (const ELFYAML::Relocation &Rel : *Section.Relocations)
+      OffsetMask |= Rel.Offset;
+  const int Shift = llvm::countr_zero(OffsetMask);
+  if (IsCrel)
+    CBA.writeULEB128(Section.Relocations->size() * 8 + 4 + Shift);
   for (const ELFYAML::Relocation &Rel : *Section.Relocations) {
     const bool IsDynamic = Section.Link && (*Section.Link == ".dynsym");
-    unsigned SymIdx =
+    uint32_t CurSymidx =
         Rel.Symbol ? toSymbolIndex(*Rel.Symbol, Section.Name, IsDynamic) : 0;
-    if (IsRela) {
+    if (IsCrel) {
----------------
smithp35 wrote:

Could it be worth abstracting out some of the calculations into inline functions that could be called from both here and `ElfObjectWriter.cpp`?

I'm on the fence about this myself as while it would help with consistency between the two implementations, and potentially any additional implementation of the algorithm the pieces of the algorithm that can be extracted is small.

https://github.com/llvm/llvm-project/pull/91280