[PATCH] D71735: [ELF] Don't suggest an alternative spelling for a symbol in a discarded section

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: grimar, peter.smith, ruiu.
Herald added subscribers: llvm-commits, luismarques, s.egerton, lenary, PkmX, simoncook, arichardson, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

For undef-not-suggest.s, we currently make redundant alternative
spelling suggestions:

  ld.lld: error: relocation refers to a discarded section: .text.foo
  >>> defined in a.o
  >>> section group signature: foo
  >>> prevailing definition is in a.o
  >>> referenced by a.o:(.rodata+0x0)
  >>> did you mean:
  >>> defined in: a.o
  
  ld.lld: error: relocation refers to a symbol in a discarded section: foo
  >>> defined in a.o
  >>> section group signature: foo
  >>> prevailing definition is in a.o
  >>> referenced by a.o:(.rodata+0x8)
  >>> did you mean: for
  >>> defined in: a.o

On many targets, a relocation referencing a local symbol is represented
as a section symbol. RISC-V is not, so it allows us to enhance the test
a bit.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D71735

Files:
  lld/ELF/Relocations.cpp
  lld/test/ELF/undef-not-suggest.s


Index: lld/test/ELF/undef-not-suggest.s
===================================================================
--- /dev/null
+++ lld/test/ELF/undef-not-suggest.s
@@ -0,0 +1,25 @@
+# REQUIRES: riscv
+## Check we don't suggest alternative spelling for relocations to symbols
+## defined in discarded sections.
+
+# RUN: llvm-mc -filetype=obj -triple=riscv64 %s -o %t.o
+# RUN: not ld.lld %t.o %t.o -o /dev/null 2>&1 | FileCheck %s
+
+# CHECK-NOT: did you mean:
+
+.section .text.foo,"axG",%progbits,foo,comdat
+foo:
+
+.section .rodata
+## Relocation which references .text.foo .
+## Check we don't suggest .data, which has an empty name.
+.quad .text.foo
+
+## Relocation which references foo (this is not represented a section symbol on
+## RISC-V). Check we don't suggest for.
+.quad foo
+
+## .data is referenced, so there is a section symbol for .data
+.section .data
+.quad .data
+for:
Index: lld/ELF/Relocations.cpp
===================================================================
--- lld/ELF/Relocations.cpp
+++ lld/ELF/Relocations.cpp
@@ -714,12 +714,20 @@
 // Suggest an alternative spelling of an "undefined symbol" diagnostic. Returns
 // the suggested symbol, which is either in the symbol table, or in the same
 // file of sym.
+template <class ELFT>
 static const Symbol *getAlternativeSpelling(const Undefined &sym,
                                             std::string &pre_hint,
                                             std::string &post_hint) {
-  // Build a map of local defined symbols.
   DenseMap<StringRef, const Symbol *> map;
   if (sym.file && !isa<SharedFile>(sym.file)) {
+    // If sym is a symbol defined in a discarded section, maybeReportDiscarded()
+    // will give an error. Don't suggest an alternative spelling.
+    auto *file = dyn_cast_or_null<ObjFile<ELFT>>(sym.file);
+    if (file && sym.discardedSecIdx != 0 &&
+        file->getSections()[sym.discardedSecIdx] == &InputSection::discarded)
+      return nullptr;
+
+    // Build a map of local defined symbols.
     for (const Symbol *s : sym.file->getSymbols())
       if (s->isLocal() && s->isDefined())
         map.try_emplace(s->getName(), s);
@@ -865,8 +873,8 @@
 
   if (correctSpelling) {
     std::string pre_hint = ": ", post_hint;
-    if (const Symbol *corrected =
-            getAlternativeSpelling(cast<Undefined>(sym), pre_hint, post_hint)) {
+    if (const Symbol *corrected = getAlternativeSpelling<ELFT>(
+            cast<Undefined>(sym), pre_hint, post_hint)) {
       msg += "\n>>> did you mean" + pre_hint + toString(*corrected) + post_hint;
       if (corrected->file)
         msg += "\n>>> defined in: " + toString(corrected->file);


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