[ELF] Demote symbols in /DISCARD/ discarded sections to Undefined (#69295)
When an input section is matched by /DISCARD/ in a linker script, GNU ld
reports errors for relocations referencing symbols defined in the section:
`.aaa' referenced in section `.bbb' of a.o: defined in discarded section `.aaa' of a.o
Implement the error by demoting eligible symbols to `Undefined` and changing
STB_WEAK to STB_GLOBAL. As a side benefit, in relocatable links, relocations
referencing symbols defined relative to /DISCARD/ discarded sections no longer
set symbol/type to zeros.
It's arguable whether a weak reference to a discarded symbol should lead to
errors. GNU ld reports an error and our demoting approach reports an error as
well.
Close #58891
Co-authored-by: Bevin Hansson <[email protected]>
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
index 07061d3..671eb56 100644
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -316,12 +316,13 @@
if (!config->warnSymbolOrdering)
return;
- // If UnresolvedPolicy::Ignore is used, no "undefined symbol" error/warning
- // is emitted. It makes sense to not warn on undefined symbols.
+ // If UnresolvedPolicy::Ignore is used, no "undefined symbol" error/warning is
+ // emitted. It makes sense to not warn on undefined symbols (excluding those
+ // demoted by demoteSymbols).
//
// Note, ld.bfd --symbol-ordering-file= does not warn on undefined symbols,
// but we don't have to be compatible here.
- if (sym->isUndefined() &&
+ if (sym->isUndefined() && !cast<Undefined>(sym)->discardedSecIdx &&
config->unresolvedSymbols == UnresolvedPolicy::Ignore)
return;
@@ -330,9 +331,12 @@
auto report = [&](StringRef s) { warn(toString(file) + s + sym->getName()); };
- if (sym->isUndefined())
- report(": unable to order undefined symbol: ");
- else if (sym->isShared())
+ if (sym->isUndefined()) {
+ if (cast<Undefined>(sym)->discardedSecIdx)
+ report(": unable to order discarded symbol: ");
+ else
+ report(": unable to order undefined symbol: ");
+ } else if (sym->isShared())
report(": unable to order shared symbol: ");
else if (d && !d->section)
report(": unable to order absolute symbol: ");
