[lld] [lld][ELF] Demote symbols in discarded sections to Undefined. (PR #68777)

[Peter Smith via llvm-commits]

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@@ -3062,6 +3062,30 @@ void LinkerDriver::link(opt::InputArgList &args) {
     script->addOrphanSections();
   }
 
+  // Explicitly demote symbols which didn't get placed. If we don't, any
+  // symbol in a discarded section will still be considered defined, even
+  // though it didn't end up in the output, and we get silently broken
+  // binaries.
+  if (script->hasSectionsCommand) {
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smithp35 wrote:

Could it be worth adding a script->seenDiscard variable so that this potentially expensive operation is only done when someone has used /DISCARD/ ?

https://github.com/llvm/llvm-project/pull/68777