#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"
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");
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);
--- /dev/null
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | elf-dump | FileCheck %s
+
+// This is a long test that checks that the aliases created by weakref are
+// never in the symbol table and that the only case it causes a symbol to
+// be output as a weak undefined symbol is if that variable is not defined
+// in this file and all the references to it are done via the alias.
+
+ .weakref foo1, bar1
+
+ .weakref foo2, bar2
+ .long bar2
+
+ .weakref foo3, bar3
+ .long foo3
+
+ .weakref foo4, bar4
+ .long foo4
+ .long bar4
+
+ .weakref foo5, bar5
+ .long bar5
+ .long foo5
+
+bar6:
+ .weakref foo6, bar6
+
+bar7:
+ .weakref foo7, bar7
+ .long bar7
+
+bar8:
+ .weakref foo8, bar8
+ .long foo8
+
+bar9:
+ .weakref foo9, bar9
+ .long foo9
+ .long bar9
+
+bar10:
+ .global bar10
+ .weakref foo10, bar10
+ .long bar10
+ .long foo10
+
+bar11:
+ .global bar11
+ .weakref foo11, bar11
+
+bar12:
+ .global bar12
+ .weakref foo12, bar12
+ .long bar12
+
+bar13:
+ .global bar13
+ .weakref foo13, bar13
+ .long foo13
+
+bar14:
+ .global bar14
+ .weakref foo14, bar14
+ .long foo14
+ .long bar14
+
+bar15:
+ .global bar15
+ .weakref foo15, bar15
+ .long bar15
+ .long foo15
+
+// CHECK: # Symbol 0x00000000
+// CHECK-NEXT: (('st_name', 0x00000000) # ''
+// CHECK-NEXT: ('st_bind', 0x00000000)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000000)
+// CHECK-NEXT: ('st_value', 0x00000000)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000001
+// CHECK-NEXT: (('st_name', 0x00000015) # 'bar6'
+// CHECK-NEXT: ('st_bind', 0x00000000)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x00000018)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000002
+// CHECK-NEXT: (('st_name', 0x0000001a) # 'bar7'
+// CHECK-NEXT: ('st_bind', 0x00000000)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x00000018)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000003
+// CHECK-NEXT: (('st_name', 0x0000001f) # 'bar8'
+// CHECK-NEXT: ('st_bind', 0x00000000)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x0000001c)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000004
+// CHECK-NEXT: (('st_name', 0x00000024) # 'bar9'
+// CHECK-NEXT: ('st_bind', 0x00000000)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x00000020)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000005
+// CHECK-NEXT: (('st_name', 0x00000000) # ''
+// CHECK-NEXT: ('st_bind', 0x00000000)
+// CHECK-NEXT: ('st_type', 0x00000003)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x00000000)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000006
+// CHECK-NEXT: (('st_name', 0x00000000) # ''
+// CHECK-NEXT: ('st_bind', 0x00000000)
+// CHECK-NEXT: ('st_type', 0x00000003)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000002)
+// CHECK-NEXT: ('st_value', 0x00000000)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000007
+// CHECK-NEXT: (('st_name', 0x00000000) # ''
+// CHECK-NEXT: ('st_bind', 0x00000000)
+// CHECK-NEXT: ('st_type', 0x00000003)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000003)
+// CHECK-NEXT: ('st_value', 0x00000000)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000008
+// CHECK-NEXT: (('st_name', 0x00000029) # 'bar10'
+// CHECK-NEXT: ('st_bind', 0x00000001)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x00000028)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000009
+// CHECK-NEXT: (('st_name', 0x0000002f) # 'bar11'
+// CHECK-NEXT: ('st_bind', 0x00000001)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x00000030)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x0000000a
+// CHECK-NEXT: (('st_name', 0x00000035) # 'bar12'
+// CHECK-NEXT: ('st_bind', 0x00000001)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x00000030)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x0000000b
+// CHECK-NEXT: (('st_name', 0x0000003b) # 'bar13'
+// CHECK-NEXT: ('st_bind', 0x00000001)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x00000034)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x0000000c
+// CHECK-NEXT: (('st_name', 0x00000041) # 'bar14'
+// CHECK-NEXT: ('st_bind', 0x00000001)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x00000038)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x0000000d
+// CHECK-NEXT: (('st_name', 0x00000047) # 'bar15'
+// CHECK-NEXT: ('st_bind', 0x00000001)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000001)
+// CHECK-NEXT: ('st_value', 0x00000040)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x0000000e
+// CHECK-NEXT: (('st_name', 0x00000001) # 'bar2'
+// CHECK-NEXT: ('st_bind', 0x00000001)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000000)
+// CHECK-NEXT: ('st_value', 0x00000000)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x0000000f
+// CHECK-NEXT: (('st_name', 0x00000006) # 'bar3'
+// CHECK-NEXT: ('st_bind', 0x00000002)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000000)
+// CHECK-NEXT: ('st_value', 0x00000000)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000010
+// CHECK-NEXT: (('st_name', 0x0000000b) # 'bar4'
+// CHECK-NEXT: ('st_bind', 0x00000001)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000000)
+// CHECK-NEXT: ('st_value', 0x00000000)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: # Symbol 0x00000011
+// CHECK-NEXT: (('st_name', 0x00000010) # 'bar5'
+// CHECK-NEXT: ('st_bind', 0x00000001)
+// CHECK-NEXT: ('st_type', 0x00000000)
+// CHECK-NEXT: ('st_other', 0x00000000)
+// CHECK-NEXT: ('st_shndx', 0x00000000)
+// CHECK-NEXT: ('st_value', 0x00000000)
+// CHECK-NEXT: ('st_size', 0x00000000)
+// CHECK-NEXT: ),
+// CHECK-NEXT: ])