[llvm] [AIX] Handle toc-data offset overflowing 16-bits (PR #80092)

[Sean Fertile via llvm-commits]

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@@ -736,11 +736,26 @@ void XCOFFObjectWriter::recordRelocation(MCAssembler &Asm,
     } else {
       // The FixedValue should be the TOC entry offset from the TOC-base plus
       // any constant offset value.
-      const int64_t TOCEntryOffset = SectionMap[SymASec]->Address -
-                                     TOCCsects.front().Address +
-                                     Target.getConstant();
+      int64_t TOCEntryOffset = SectionMap[SymASec]->Address -
+                               TOCCsects.front().Address + Target.getConstant();
+      // For small code model, if the TOCEntryOffset overflows the 16-bit value,
+      // we truncate it back down to 16 bits. The linker will be able to insert
+      // fix-up code when needed.
+      // For non toc-data symbols, we already did the truncation in
+      // PPCAsmPrinter.cpp through setting Target.getConstant() in the
+      // expression above by calling getTOCEntryLoadingExprForXCOFF for the
+      // various TOC PseudoOps.
+      // For toc-data symbols, we were not able to calculate the offset from
+      // the TOC in PPCAsmPrinter.cpp since the TOC has not been finalized at
+      // that point, so we are adjusting it here though
+      // llvm::SignExtend64<16>(TOCEntryOffset);
+      // TODO: Since the time that the handling for offsets over 16-bits was
+      // added in PPCAsmPrinter.cpp using getTOCEntryLoadingExprForXCOFF, the
+      // system assembler and linker have been updated to be able to handle the
+      // overflowing offsets, so we no longer need to keep
+      // getTOCEntryLoadingExprForXCOFF.
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mandlebug wrote:

Is the situation that all supported OS levels would now have an assembler that will produce the expected results without the workaround or is it just new OS levels have the fix and we have to still wait until OS levels with the old assemblers drop off the supported list over time?

https://github.com/llvm/llvm-project/pull/80092