[llvm] [yaml2obj][XOFF] Update yaml2obj for XCOFF to create valid XCOFF files in more cases. (PR #77620)

[James Henderson via llvm-commits]

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@@ -98,11 +98,26 @@ bool XCOFFWriter::nameShouldBeInStringTable(StringRef SymbolName) {
 bool XCOFFWriter::initRelocations(uint64_t &CurrentOffset) {
   for (XCOFFYAML::Section &InitSection : InitSections) {
     if (!InitSection.Relocations.empty()) {
-      InitSection.NumberOfRelocations = InitSection.Relocations.size();
-      InitSection.FileOffsetToRelocations = CurrentOffset;
       uint64_t RelSize = Is64Bit ? XCOFF::RelocationSerializationSize64
                                  : XCOFF::RelocationSerializationSize32;
-      CurrentOffset += InitSection.NumberOfRelocations * RelSize;
+      const uint64_t UsedSize = RelSize * InitSection.Relocations.size();
+
+      // If NumberOfRelocations was specified, we use it, even if it's
+      // not consistent with the number of provided relocations
+      if (!InitSection.NumberOfRelocations)
+        InitSection.NumberOfRelocations = InitSection.Relocations.size();
+
+      // If the YAML file specified an offset to relocations, we use it.
+      if (InitSection.FileOffsetToRelocations) {
+        if (CurrentOffset > InitSection.FileOffsetToRelocations) {
+          ErrHandler("Specified FileOffsetToRelocations will overwrite"
+                     "existing data");
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jh7370 wrote:

Nit: this does not conform to the error/warning message style in the coding standards (lower-case first letter needed, plus additional context, e.g. what the `CurrentOffset` value actually is).

https://github.com/llvm/llvm-project/pull/77620