[lld] [ELF] Synthesize STT_FILE if necessary (PR #209087)

[Fangrui Song via llvm-commits]

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@@ -669,6 +671,16 @@ class SymbolTableBaseSection : public SyntheticSection {
   // A vector of symbols and their string table offsets.
   SmallVector<SymbolTableEntry, 0> symbols;
 
+  // Synthetic STT_FILE with an empty name, added by maybeAddSttFile and placed
+  // by sortSymTabSymbols before all symbols demoted to STB_LOCAL.
+  Defined *synthSttFileSym = nullptr;
+
+  // symbols[firstGlobalIdx, synthSttFileIdx) were originally non-local and may
+  // be converted to local. synthSttFileIdx is where synthSttFileSym lands.
+  // Locals added later (thunks via addSyntheticLocal) fall outside and stay
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MaskRay wrote:

Thanks for the suggestion.
I've gone ahead and attributed thunk symbols to the synthesized STT_FILE symbol with empty name. Simplified the comment here. Since there are extensive comments in SymbolTableBaseSection::sortSymTabSymbols and SymbolTableBaseSection::maybeAddSttFile, I've trimmed the comment here.

https://github.com/llvm/llvm-project/pull/209087