Implement .weakref.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117911 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/ELFObjectWriter.cpp b/lib/MC/ELFObjectWriter.cpp
index 850983f..a0e326d 100644
--- a/lib/MC/ELFObjectWriter.cpp
+++ b/lib/MC/ELFObjectWriter.cpp
@@ -143,6 +143,7 @@
};
SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
+ SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
DenseMap<const MCSymbol *, const MCSymbol *> Renames;
llvm::DenseMap<const MCSectionData*,
@@ -691,7 +692,7 @@
Symbol = &AliasedSymbol(Target.getSymA()->getSymbol());
Renamed = Renames.lookup(Symbol);
if (!Renamed)
- Renamed = Symbol;
+ Renamed = &Target.getSymA()->getSymbol();
MCSymbolData &SD = Asm.getSymbolData(*Symbol);
MCFragment *F = SD.getFragment();
@@ -727,6 +728,10 @@
Value += Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD);
} else {
UsedInReloc.insert(Renamed);
+ MCSymbolData &RenamedSD = Asm.getSymbolData(*Renamed);
+ if (RenamedSD.getFlags() & ELF_Other_Weakref) {
+ WeakrefUsedInReloc.insert(Symbol);
+ }
Index = -1;
}
Addend = Value;
@@ -901,6 +906,9 @@
static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
bool Used, bool Renamed) {
+ if (Data.getFlags() & ELF_Other_Weakref)
+ return false;
+
if (Used)
return true;
@@ -963,7 +971,9 @@
ie = Asm.symbol_end(); it != ie; ++it) {
const MCSymbol &Symbol = it->getSymbol();
- if (!isInSymtab(Asm, *it, UsedInReloc.count(&Symbol),
+ bool Used = UsedInReloc.count(&Symbol);
+ bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
+ if (!isInSymtab(Asm, *it, Used || WeakrefUsed,
Renames.count(&Symbol)))
continue;
@@ -972,6 +982,9 @@
bool Local = isLocal(*it);
const MCSymbol &RefSymbol = AliasedSymbol(Symbol);
+ if (RefSymbol.isUndefined() && !Used && WeakrefUsed)
+ SetBinding(*it, ELF::STB_WEAK);
+
if (it->isCommon()) {
assert(!Local);
MSD.SectionIndex = ELF::SHN_COMMON;
diff --git a/lib/MC/MCAsmStreamer.cpp b/lib/MC/MCAsmStreamer.cpp
index 6c240cf..ca8dc96 100644
--- a/lib/MC/MCAsmStreamer.cpp
+++ b/lib/MC/MCAsmStreamer.cpp
@@ -113,6 +113,7 @@
virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
+ virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);
virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
@@ -258,6 +259,11 @@
Symbol->setVariableValue(Value);
}
+void MCAsmStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
+ OS << ".weakref " << *Alias << ", " << *Symbol;
+ EmitEOL();
+}
+
void MCAsmStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
MCSymbolAttr Attribute) {
switch (Attribute) {
diff --git a/lib/MC/MCELFStreamer.cpp b/lib/MC/MCELFStreamer.cpp
index 65a0a7d..e794e57 100644
--- a/lib/MC/MCELFStreamer.cpp
+++ b/lib/MC/MCELFStreamer.cpp
@@ -24,6 +24,7 @@
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCSymbol.h"
+#include "llvm/MC/MCValue.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/ErrorHandling.h"
@@ -51,6 +52,7 @@
virtual void EmitLabel(MCSymbol *Symbol);
virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
+ virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);
virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
assert(0 && "ELF doesn't support this directive");
@@ -193,6 +195,64 @@
Symbol->setVariableValue(AddValueSymbols(Value));
}
+// This is a hack. To be able to implement weakrefs the writer has to be able
+// to distinguish
+// .weakref foo, bar
+// .long foo
+// from
+// .weakref foo, bar
+// .long bar
+// since the first case should produce a weak undefined reference and the second
+// one a strong one.
+// If we created foo as a regular alias pointing to bar (foo = bar), then
+// MCExpr::EvaluateAsRelocatable would recurse on foo and the writer would
+// never see it used in a relocation.
+// What we do is create a MCTargetExpr that when evaluated produces a symbol
+// ref to a temporary symbol. This temporary symbol in turn is a variable
+// that equals the original symbol (tmp = bar). With this hack the writer
+// gets a relocation with tmp and can correctly implement weak references.
+
+class WeakRefExpr : public MCTargetExpr {
+private:
+ const MCSymbolRefExpr *Alias;
+
+ explicit WeakRefExpr(const MCSymbolRefExpr *Alias_)
+ : MCTargetExpr(), Alias(Alias_) {}
+
+public:
+ virtual void PrintImpl(raw_ostream &OS) const {
+ llvm_unreachable("Unimplemented");
+ }
+
+ virtual bool EvaluateAsRelocatableImpl(MCValue &Res,
+ const MCAsmLayout *Layout) const {
+ Res = MCValue::get(Alias, 0, 0);
+ return true;
+ }
+
+ static const WeakRefExpr *Create(const MCSymbol *Alias, MCContext &Ctx) {
+ const MCSymbolRefExpr *A = MCSymbolRefExpr::Create(Alias, Ctx);
+ return new (Ctx) WeakRefExpr(A);
+ }
+};
+
+void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
+ getAssembler().getOrCreateSymbolData(*Symbol);
+ MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
+ AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
+
+ // Create the alias that actually points to Symbol
+ const MCSymbolRefExpr *SymRef = MCSymbolRefExpr::Create(Symbol, getContext());
+ MCSymbol *RealAlias = getContext().CreateTempSymbol();
+ RealAlias->setVariableValue(SymRef);
+
+ MCSymbolData &RealAliasSD = getAssembler().getOrCreateSymbolData(*RealAlias);
+ RealAliasSD.setFlags(RealAliasSD.getFlags() | ELF_Other_Weakref);
+
+ const MCExpr *Value = WeakRefExpr::Create(RealAlias, getContext());
+ Alias->setVariableValue(Value);
+}
+
static void SetBinding(MCSymbolData &SD, unsigned Binding) {
assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
Binding == ELF::STB_WEAK);
diff --git a/lib/MC/MCLoggingStreamer.cpp b/lib/MC/MCLoggingStreamer.cpp
index 7615745..a907c11 100644
--- a/lib/MC/MCLoggingStreamer.cpp
+++ b/lib/MC/MCLoggingStreamer.cpp
@@ -74,6 +74,11 @@
return Child->EmitAssignment(Symbol, Value);
}
+ virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
+ LogCall("EmitWeakReference");
+ return Child->EmitWeakReference(Alias, Symbol);
+ }
+
virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) {
LogCall("EmitSymbolAttribute");
return Child->EmitSymbolAttribute(Symbol, Attribute);
diff --git a/lib/MC/MCNullStreamer.cpp b/lib/MC/MCNullStreamer.cpp
index b2db410..5f29b46 100644
--- a/lib/MC/MCNullStreamer.cpp
+++ b/lib/MC/MCNullStreamer.cpp
@@ -42,6 +42,7 @@
virtual void EmitAssemblerFlag(MCAssemblerFlag Flag) {}
virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {}
+ virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol){}
virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute){}
diff --git a/lib/MC/MCObjectStreamer.cpp b/lib/MC/MCObjectStreamer.cpp
index 8a481e8..3883f12 100644
--- a/lib/MC/MCObjectStreamer.cpp
+++ b/lib/MC/MCObjectStreamer.cpp
@@ -74,6 +74,11 @@
return Value;
}
+void MCObjectStreamer::EmitWeakReference(MCSymbol *Alias,
+ const MCSymbol *Symbol) {
+ report_fatal_error("This file format doesn't support weak aliases.");
+}
+
void MCObjectStreamer::SwitchSection(const MCSection *Section) {
assert(Section && "Cannot switch to a null section!");
diff --git a/lib/MC/MCParser/ELFAsmParser.cpp b/lib/MC/MCParser/ELFAsmParser.cpp
index 62cf6c6..9883018 100644
--- a/lib/MC/MCParser/ELFAsmParser.cpp
+++ b/lib/MC/MCParser/ELFAsmParser.cpp
@@ -53,6 +53,7 @@
AddDirectiveHandler<&ELFAsmParser::ParseDirectiveType>(".type");
AddDirectiveHandler<&ELFAsmParser::ParseDirectiveIdent>(".ident");
AddDirectiveHandler<&ELFAsmParser::ParseDirectiveSymver>(".symver");
+ AddDirectiveHandler<&ELFAsmParser::ParseDirectiveWeakref>(".weakref");
}
// FIXME: Part of this logic is duplicated in the MCELFStreamer. What is
@@ -119,6 +120,7 @@
bool ParseDirectiveType(StringRef, SMLoc);
bool ParseDirectiveIdent(StringRef, SMLoc);
bool ParseDirectiveSymver(StringRef, SMLoc);
+ bool ParseDirectiveWeakref(StringRef, SMLoc);
private:
bool ParseSectionName(StringRef &SectionName);
@@ -443,6 +445,32 @@
return false;
}
+/// ParseDirectiveWeakref
+/// ::= .weakref foo, bar
+bool ELFAsmParser::ParseDirectiveWeakref(StringRef, SMLoc) {
+ // FIXME: Share code with the other alias building directives.
+
+ StringRef AliasName;
+ if (getParser().ParseIdentifier(AliasName))
+ return TokError("expected identifier in directive");
+
+ if (getLexer().isNot(AsmToken::Comma))
+ return TokError("expected a comma");
+
+ Lex();
+
+ StringRef Name;
+ if (getParser().ParseIdentifier(Name))
+ return TokError("expected identifier in directive");
+
+ MCSymbol *Alias = getContext().GetOrCreateSymbol(AliasName);
+
+ MCSymbol *Sym = getContext().GetOrCreateSymbol(Name);
+
+ getStreamer().EmitWeakReference(Alias, Sym);
+ return false;
+}
+
namespace llvm {
MCAsmParserExtension *createELFAsmParser() {
diff --git a/lib/MC/MCStreamer.cpp b/lib/MC/MCStreamer.cpp
index 54071eb..351d9fc 100644
--- a/lib/MC/MCStreamer.cpp
+++ b/lib/MC/MCStreamer.cpp
@@ -10,6 +10,7 @@
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/Twine.h"