[lld] r268649 - ELF: Undefine all symbols, not just those that we expect to be defined.
Peter Collingbourne via llvm-commits
llvm-commits at lists.llvm.org
Thu May 5 10:13:49 PDT 2016
Author: pcc
Date: Thu May 5 12:13:49 2016
New Revision: 268649
URL: http://llvm.org/viewvc/llvm-project?rev=268649&view=rev
Log:
ELF: Undefine all symbols, not just those that we expect to be defined.
This allows the combined LTO object to provide a definition with the same
name as a symbol that was internalized without causing a duplicate symbol
error. This normally happens during parallel codegen which externalizes
originally-internal symbols, for example.
In order to make this work, I needed to relax the undefined symbol error to
only report an error for symbols that are used in regular objects.
Differential Revision: http://reviews.llvm.org/D19954
Added:
lld/trunk/test/ELF/lto/parallel-internalize.ll
Modified:
lld/trunk/ELF/LTO.cpp
lld/trunk/ELF/Writer.cpp
Modified: lld/trunk/ELF/LTO.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LTO.cpp?rev=268649&r1=268648&r2=268649&view=diff
==============================================================================
--- lld/trunk/ELF/LTO.cpp (original)
+++ lld/trunk/ELF/LTO.cpp Thu May 5 12:13:49 2016
@@ -106,13 +106,6 @@ void BitcodeCompiler::add(BitcodeFile &F
SmallPtrSet<GlobalValue *, 8> Used;
collectUsedGlobalVariables(M, Used, /* CompilerUsed */ false);
- // This function is called if we know that the combined LTO object will
- // provide a definition of a symbol. It undefines the symbol so that the
- // definition in the combined LTO object will replace it when parsed.
- auto Undefine = [](Symbol *S) {
- replaceBody<Undefined>(S, S->body()->getName(), STV_DEFAULT, 0);
- };
-
for (const BasicSymbolRef &Sym : Obj->symbols()) {
uint32_t Flags = Sym.getFlags();
GlobalValue *GV = Obj->getSymbolGV(Sym.getRawDataRefImpl());
@@ -123,14 +116,30 @@ void BitcodeCompiler::add(BitcodeFile &F
Symbol *S = Syms[BodyIndex++];
if (Flags & BasicSymbolRef::SF_Undefined)
continue;
- if (!GV) {
- // Module asm symbol.
- Undefine(S);
- continue;
- }
auto *B = dyn_cast<DefinedBitcode>(S->body());
if (!B || B->File != &F)
continue;
+
+ // We collect the set of symbols we want to internalize here
+ // and change the linkage after the IRMover executed, i.e. after
+ // we imported the symbols and satisfied undefined references
+ // to it. We can't just change linkage here because otherwise
+ // the IRMover will just rename the symbol.
+ if (GV && shouldInternalize(Used, S, GV))
+ InternalizedSyms.insert(GV->getName());
+
+ // At this point we know that either the combined LTO object will provide a
+ // definition of a symbol, or we will internalize it. In either case, we
+ // need to undefine the symbol. In the former case, the real definition
+ // needs to be able to replace the original definition without conflicting.
+ // In the latter case, we need to allow the combined LTO object to provide a
+ // definition with the same name, for example when doing parallel codegen.
+ replaceBody<Undefined>(S, S->body()->getName(), STV_DEFAULT, 0);
+
+ if (!GV)
+ // Module asm symbol.
+ continue;
+
switch (GV->getLinkage()) {
default:
break;
@@ -142,16 +151,6 @@ void BitcodeCompiler::add(BitcodeFile &F
break;
}
- // We collect the set of symbols we want to internalize here
- // and change the linkage after the IRMover executed, i.e. after
- // we imported the symbols and satisfied undefined references
- // to it. We can't just change linkage here because otherwise
- // the IRMover will just rename the symbol.
- if (shouldInternalize(Used, S, GV))
- InternalizedSyms.insert(GV->getName());
- else
- Undefine(S);
-
Keep.push_back(GV);
}
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=268649&r1=268648&r2=268649&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Thu May 5 12:13:49 2016
@@ -1391,7 +1391,9 @@ template <class ELFT> void Writer<ELFT>:
if (auto *SS = dyn_cast<SharedSymbol<ELFT>>(Body))
SS->File->IsUsed = true;
- if (Body->isUndefined() && !S->isWeak())
+ // We only report undefined symbols in regular objects. This means that we
+ // will accept an undefined reference in bitcode if it can be optimized out.
+ if (S->IsUsedInRegularObj && Body->isUndefined() && !S->isWeak())
reportUndefined<ELFT>(Symtab, Body);
if (auto *C = dyn_cast<DefinedCommon>(Body))
Added: lld/trunk/test/ELF/lto/parallel-internalize.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/lto/parallel-internalize.ll?rev=268649&view=auto
==============================================================================
--- lld/trunk/test/ELF/lto/parallel-internalize.ll (added)
+++ lld/trunk/test/ELF/lto/parallel-internalize.ll Thu May 5 12:13:49 2016
@@ -0,0 +1,57 @@
+; REQUIRES: x86
+; RUN: llvm-as -o %t.bc %s
+; RUN: ld.lld -m elf_x86_64 --lto-jobs=2 -save-temps -o %t %t.bc -e foo --lto-O0
+; RUN: llvm-readobj -t -dyn-symbols %t | FileCheck %s
+; RUN: llvm-nm %t0.lto.o | FileCheck --check-prefix=CHECK0 %s
+; RUN: llvm-nm %t1.lto.o | FileCheck --check-prefix=CHECK1 %s
+
+; CHECK: Symbols [
+; CHECK-NEXT: Symbol {
+; CHECK-NEXT: Name: (0)
+; CHECK-NEXT: Value: 0x0
+; CHECK-NEXT: Size: 0
+; CHECK-NEXT: Binding: Local (0x0)
+; CHECK-NEXT: Type: None (0x0)
+; CHECK-NEXT: Other: 0
+; CHECK-NEXT: Section: Undefined (0x0)
+; CHECK-NEXT: }
+; CHECK-NEXT: Symbol {
+; CHECK-NEXT: Name: bar (5)
+; CHECK-NEXT: Value: 0x11010
+; CHECK-NEXT: Size: 8
+; CHECK-NEXT: Binding: Local (0x0)
+; CHECK-NEXT: Type: Function (0x2)
+; CHECK-NEXT: Other [ (0x2)
+; CHECK-NEXT: STV_HIDDEN (0x2)
+; CHECK-NEXT: ]
+; CHECK-NEXT: Section: .text (0x2)
+; CHECK-NEXT: }
+; CHECK-NEXT: Symbol {
+; CHECK-NEXT: Name: foo (1)
+; CHECK-NEXT: Value: 0x11000
+; CHECK-NEXT: Size: 8
+; CHECK-NEXT: Binding: Global (0x1)
+; CHECK-NEXT: Type: Function (0x2)
+; CHECK-NEXT: Other: 0
+; CHECK-NEXT: Section: .text (0x2)
+; CHECK-NEXT: }
+; CHECK-NEXT: ]
+; CHECK-NEXT: DynamicSymbols [
+; CHECK-NEXT: ]
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK0: U bar
+; CHECK0: T foo
+define void @foo() {
+ call void @bar()
+ ret void
+}
+
+; CHECK1: T bar
+; CHECK1: U foo
+define void @bar() {
+ call void @foo()
+ ret void
+}
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