[llvm] r205811 - WinCOFF: Emit common symbols as specified in the COFF spec
David Majnemer
david.majnemer at gmail.com
Tue Apr 8 15:33:41 PDT 2014
Author: majnemer
Date: Tue Apr 8 17:33:40 2014
New Revision: 205811
URL: http://llvm.org/viewvc/llvm-project?rev=205811&view=rev
Log:
WinCOFF: Emit common symbols as specified in the COFF spec
Summary:
Local common symbols were properly inserted into the .bss section.
However, putting external common symbols in the .bss section would give
them a strong definition.
Instead, encode them as undefined, external symbols who's symbol value
is equivalent to their size.
Reviewers: Bigcheese, rafael, rnk
CC: llvm-commits
Differential Revision: http://reviews.llvm.org/D3324
Modified:
llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
llvm/trunk/lib/MC/MCObjectFileInfo.cpp
llvm/trunk/lib/MC/WinCOFFObjectWriter.cpp
llvm/trunk/lib/MC/WinCOFFStreamer.cpp
llvm/trunk/test/MC/COFF/comm.ll
llvm/trunk/test/MC/COFF/comm.s
Modified: llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp?rev=205811&r1=205810&r2=205811&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (original)
+++ llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp Tue Apr 8 17:33:40 2014
@@ -755,7 +755,7 @@ const MCSection *TargetLoweringObjectFil
static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
if (Kind.isText())
return ".text";
- if (Kind.isBSS ())
+ if (Kind.isBSS())
return ".bss";
if (Kind.isThreadLocal())
return ".tls$";
@@ -781,7 +781,7 @@ SelectSectionForGlobal(const GlobalValue
// Section names depend on the name of the symbol which is not feasible if the
// symbol has private linkage.
if ((GV->isWeakForLinker() || EmitUniquedSection) &&
- !GV->hasPrivateLinkage()) {
+ !GV->hasPrivateLinkage() && !Kind.isCommon()) {
const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
unsigned Characteristics = getCOFFSectionFlags(Kind);
@@ -802,7 +802,10 @@ SelectSectionForGlobal(const GlobalValue
if (Kind.isReadOnly())
return ReadOnlySection;
- if (Kind.isBSS())
+ // Note: we claim that common symbols are put in BSSSection, but they are
+ // really emitted with the magic .comm directive, which creates a symbol table
+ // entry but not a section.
+ if (Kind.isBSS() || Kind.isCommon())
return BSSSection;
return DataSection;
Modified: llvm/trunk/lib/MC/MCObjectFileInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCObjectFileInfo.cpp?rev=205811&r1=205810&r2=205811&view=diff
==============================================================================
--- llvm/trunk/lib/MC/MCObjectFileInfo.cpp (original)
+++ llvm/trunk/lib/MC/MCObjectFileInfo.cpp Tue Apr 8 17:33:40 2014
@@ -548,6 +548,10 @@ void MCObjectFileInfo::InitELFMCObjectFi
void MCObjectFileInfo::InitCOFFMCObjectFileInfo(Triple T) {
+ // The object file format cannot represent common symbols with explicit
+ // alignments.
+ CommDirectiveSupportsAlignment = false;
+
// COFF
BSSSection =
Ctx->getCOFFSection(".bss",
Modified: llvm/trunk/lib/MC/WinCOFFObjectWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/WinCOFFObjectWriter.cpp?rev=205811&r1=205810&r2=205811&view=diff
==============================================================================
--- llvm/trunk/lib/MC/WinCOFFObjectWriter.cpp (original)
+++ llvm/trunk/lib/MC/WinCOFFObjectWriter.cpp Tue Apr 8 17:33:40 2014
@@ -394,7 +394,7 @@ void WinCOFFObjectWriter::DefineSection(
SectionMap[&SectionData.getSection()] = coff_section;
}
-/// This function takes a section data object from the assembler
+/// This function takes a symbol data object from the assembler
/// and creates the associated COFF symbol staging object.
void WinCOFFObjectWriter::DefineSymbol(MCSymbolData const &SymbolData,
MCAssembler &Assembler,
@@ -443,6 +443,8 @@ void WinCOFFObjectWriter::DefineSymbol(M
int64_t Addr;
if (Symbol.getVariableValue()->EvaluateAsAbsolute(Addr, Layout))
coff_symbol->Data.Value = Addr;
+ } else if (SymbolData.isExternal() && SymbolData.isCommon()) {
+ coff_symbol->Data.Value = SymbolData.getCommonSize();
}
coff_symbol->Data.Type = (ResSymData.getFlags() & 0x0000FFFF) >> 0;
Modified: llvm/trunk/lib/MC/WinCOFFStreamer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/WinCOFFStreamer.cpp?rev=205811&r1=205810&r2=205811&view=diff
==============================================================================
--- llvm/trunk/lib/MC/WinCOFFStreamer.cpp (original)
+++ llvm/trunk/lib/MC/WinCOFFStreamer.cpp Tue Apr 8 17:33:40 2014
@@ -45,9 +45,6 @@ public:
MCCodeEmitter &CE,
raw_ostream &OS);
- void AddCommonSymbol(MCSymbol *Symbol, uint64_t Size,
- unsigned ByteAlignment, bool External);
-
// MCStreamer interface
void InitSections() override;
@@ -101,26 +98,6 @@ WinCOFFStreamer::WinCOFFStreamer(MCConte
MCCodeEmitter &CE, raw_ostream &OS)
: MCObjectStreamer(Context, MAB, OS, &CE), CurSymbol(NULL) {}
-void WinCOFFStreamer::AddCommonSymbol(MCSymbol *Symbol, uint64_t Size,
- unsigned ByteAlignment, bool External) {
- assert(!Symbol->isInSection() && "Symbol must not already have a section!");
-
- const MCSection *Section = getContext().getObjectFileInfo()->getBSSSection();
- MCSectionData &SectionData = getAssembler().getOrCreateSectionData(*Section);
- if (SectionData.getAlignment() < ByteAlignment)
- SectionData.setAlignment(ByteAlignment);
-
- MCSymbolData &SymbolData = getAssembler().getOrCreateSymbolData(*Symbol);
- SymbolData.setExternal(External);
-
- AssignSection(Symbol, Section);
-
- if (ByteAlignment != 1)
- new MCAlignFragment(ByteAlignment, 0, 0, ByteAlignment, &SectionData);
-
- SymbolData.setFragment(new MCFillFragment(0, 0, Size, &SectionData));
-}
-
// MCStreamer interface
void WinCOFFStreamer::InitSections() {
@@ -244,15 +221,38 @@ void WinCOFFStreamer::EmitCommonSymbol(M
assert((Symbol->isInSection()
? Symbol->getSection().getVariant() == MCSection::SV_COFF
: true) && "Got non-COFF section in the COFF backend!");
- AddCommonSymbol(Symbol, Size, ByteAlignment, true);
+
+ if (ByteAlignment > 32)
+ report_fatal_error(
+ "The linker won't align common symbols beyond 32 bytes.");
+
+ AssignSection(Symbol, NULL);
+
+ MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
+ SD.setExternal(true);
+ SD.setCommon(Size, ByteAlignment);
}
void WinCOFFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment) {
- assert((Symbol->isInSection()
- ? Symbol->getSection().getVariant() == MCSection::SV_COFF
- : true) && "Got non-COFF section in the COFF backend!");
- AddCommonSymbol(Symbol, Size, ByteAlignment, false);
+ assert(!Symbol->isInSection() && "Symbol must not already have a section!");
+
+ const MCSection *Section = getContext().getObjectFileInfo()->getBSSSection();
+ MCSectionData &SectionData = getAssembler().getOrCreateSectionData(*Section);
+ if (SectionData.getAlignment() < ByteAlignment)
+ SectionData.setAlignment(ByteAlignment);
+
+ MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
+ SD.setExternal(false);
+
+ AssignSection(Symbol, Section);
+
+ if (ByteAlignment != 1)
+ new MCAlignFragment(ByteAlignment, /*_Value=*/0, /*_ValueSize=*/0,
+ ByteAlignment, &SectionData);
+
+ SD.setFragment(
+ new MCFillFragment(/*_Value=*/0, /*_ValueSize=*/0, Size, &SectionData));
}
void WinCOFFStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
Modified: llvm/trunk/test/MC/COFF/comm.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/COFF/comm.ll?rev=205811&r1=205810&r2=205811&view=diff
==============================================================================
--- llvm/trunk/test/MC/COFF/comm.ll (original)
+++ llvm/trunk/test/MC/COFF/comm.ll Tue Apr 8 17:33:40 2014
@@ -9,5 +9,5 @@
; CHECK: .lcomm _a,1
; CHECK: .lcomm _b,8,8
; .comm uses log2 alignment
-; CHECK: .comm _c,1,0
-; CHECK: .comm _d,8,3
+; CHECK: .comm _c,1
+; CHECK: .comm _d,8
Modified: llvm/trunk/test/MC/COFF/comm.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/COFF/comm.s?rev=205811&r1=205810&r2=205811&view=diff
==============================================================================
--- llvm/trunk/test/MC/COFF/comm.s (original)
+++ llvm/trunk/test/MC/COFF/comm.s Tue Apr 8 17:33:40 2014
@@ -1,7 +1,7 @@
// RUN: llvm-mc -filetype=obj -triple i686-pc-win32 %s | llvm-readobj -t | FileCheck %s
.lcomm _a,4,4
-.comm _b, 4, 2
+.comm _b, 4
// CHECK: Symbol {
@@ -17,7 +17,7 @@
// CHECK: Symbol {
// CHECK: Name: _b
// CHECK-NEXT: Value: 4
-// CHECK-NEXT: Section: .bss
+// CHECK-NEXT: Section: (0)
// CHECK-NEXT: BaseType: Null
// CHECK-NEXT: ComplexType: Null
// CHECK-NEXT: StorageClass: External
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