[PATCH] D25240: [ELF] Emit warning instead of error, when undefined symbol is not really used.

[Eugene Leviant via llvm-commits]

evgeny777 created this revision.
evgeny777 added reviewers: ruiu, rafael.
evgeny777 added subscribers: grimar, ikudrin, llvm-commits.
evgeny777 set the repository for this revision to rL LLVM.
evgeny777 added a project: lld.

The situation when undefined symbol is not used often takes place, when compiler flags -ffunction-sections -fdata-sections are used in conjunction with linker flag --gc-sections.
In such case we can have undefined symbol which is used by some function collected by linker GC. Both gold and ld add undefined symbol to symtab without reporting any error or warning. This patch makes lld to emit warning instead of error in such cases.


Repository:
  rL LLVM

https://reviews.llvm.org/D25240

Files:
  ELF/Relocations.cpp
  ELF/Symbols.h
  ELF/Writer.cpp
  test/ELF/libsearch.s
  test/ELF/sysroot.s


Index: test/ELF/sysroot.s
===================================================================
--- test/ELF/sysroot.s
+++ test/ELF/sysroot.s
@@ -7,7 +7,7 @@
 // REQUIRES: x86
 
 // Should not link because of undefined symbol _bar
-// RUN: not ld.lld -o %t/r %t/m.o 2>&1 \
+// RUN: ld.lld -o %t/r %t/m.o 2>&1 \
 // RUN:     | FileCheck --check-prefix=UNDEFINED %s
 // UNDEFINED: undefined symbol: _bar
 
Index: test/ELF/libsearch.s
===================================================================
--- test/ELF/libsearch.s
+++ test/ELF/libsearch.s
@@ -16,7 +16,7 @@
 // NOLIBRARY: missing arg value for "-l", expected 1 argument.
 
 // Should not link because of undefined symbol _bar
-// RUN: not ld.lld -o %t3 %t.o 2>&1 \
+// RUN: ld.lld -o %t3 %t.o 2>&1 \
 // RUN:   | FileCheck --check-prefix=UNDEFINED %s
 // UNDEFINED: undefined symbol: _bar
 
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -317,9 +317,10 @@
   std::string Msg = "undefined symbol: ";
   Msg += Config->Demangle ? demangle(Sym->getName()) : Sym->getName().str();
 
+  bool Unused = !Sym->IsRelocTarget && !Sym->symbol()->includeInDynsym();
   if (Sym->File)
     Msg += " in " + getFilename(Sym->File);
-  if (Config->UnresolvedSymbols == UnresolvedPolicy::Warn)
+  if (Config->UnresolvedSymbols == UnresolvedPolicy::Warn || Unused)
     warn(Msg);
   else
     error(Msg);
Index: ELF/Symbols.h
===================================================================
--- ELF/Symbols.h
+++ ELF/Symbols.h
@@ -52,7 +52,7 @@
     LazyObjectKind,
   };
 
-  SymbolBody(Kind K) : SymbolKind(K) {}
+  SymbolBody(Kind K) : SymbolKind(K), IsRelocTarget(false) {}
 
   Symbol *symbol();
   const Symbol *symbol() const {
@@ -121,6 +121,9 @@
   // True if this symbol has an entry in the global part of MIPS GOT.
   unsigned IsInGlobalMipsGot : 1;
 
+  // True if the symbol is relocation target.
+  unsigned IsRelocTarget : 1;
+
   // The following fields have the same meaning as the ELF symbol attributes.
   uint8_t Type;    // symbol type
   uint8_t StOther; // st_other field value
Index: ELF/Relocations.cpp
===================================================================
--- ELF/Relocations.cpp
+++ ELF/Relocations.cpp
@@ -557,6 +557,7 @@
     const RelTy &RI = *I;
     SymbolBody &Body = File.getRelocTargetSym(RI);
     uint32_t Type = RI.getType(Config->Mips64EL);
+    Body.IsRelocTarget = true;
 
     RelExpr Expr = Target->getRelExpr(Type, Body);
     bool Preemptible = isPreemptible(Body, Type);


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D25240.73488.patch
Type: text/x-patch
Size: 2560 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20161004/7583c865/attachment-0001.bin>