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Look through variables when computing relocations. 

Given

bar = foo + 4
	.long bar

MC would eat the 4. GNU as includes it in the relocation. The rule seems to be
that a variable that defines a symbol is used in the relocation and one that
does not define a symbol is evaluated and the result included in the relocation.

Fixing this unfortunately required some other changes:

* Since the variable is now evaluated, it would prevent the ELF writer from
  noticing the weakref marker the elf streamer uses. This patch then replaces
  that with a VariantKind in MCSymbolRefExpr.

* Using VariantKind then requires us to look past other VariantKind to see

	.weakref	bar,foo
	call	bar@PLT

  doing this also fixes

	zed = foo +2
	call zed@PLT

  so that is a good thing.

* Looking past VariantKind means that the relocation selection has to use
  the fixup instead of the target.

This is a reboot of the previous fixes for MC. I will watch the sanitizer
buildbot and wait for a build before adding back the previous fixes.

llvm-svn: 204294
This commit is contained in:
Rafael Espindola 2014-03-20 02:12:01 +00:00
parent 05c152b5d1
commit 7fadc0ea7d
14 changed files with 137 additions and 35 deletions
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3
llvm/include/llvm/MC/MCELFSymbolFlags.h
View File

@ -51,8 +51,7 @@ namespace llvm {
ELF_STV_Hidden = (ELF::STV_HIDDEN << ELF_STV_Shift),
ELF_STV_Protected = (ELF::STV_PROTECTED << ELF_STV_Shift),
ELF_Other_Weakref = (1 << ELF_Other_Shift),
ELF_Other_ThumbFunc = (2 << ELF_Other_Shift)
ELF_Other_ThumbFunc = (1 << ELF_Other_Shift)
};
} // end namespace llvm

1
llvm/include/llvm/MC/MCExpr.h
View File

@ -160,6 +160,7 @@ public:
VK_DTPOFF,
VK_TLVP, // Mach-O thread local variable relocation
VK_SECREL,
VK_WEAKREF, // The link between the symbols in .weakref foo, bar
VK_ARM_NONE,
VK_ARM_TARGET1,

3
llvm/include/llvm/MC/MCFixup.h
View File

@ -10,6 +10,7 @@
#ifndef LLVM_MC_MCFIXUP_H
#define LLVM_MC_MCFIXUP_H
#include "llvm/MC/MCExpr.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/SMLoc.h"
@ -87,6 +88,8 @@ public:
MCFixupKind getKind() const { return MCFixupKind(Kind); }
MCSymbolRefExpr::VariantKind getAccessVariant() const;
uint32_t getOffset() const { return Offset; }
void setOffset(uint32_t Value) { Offset = Value; }

1
llvm/lib/MC/CMakeLists.txt
View File

@ -16,6 +16,7 @@ add_llvm_library(LLVMMC
MCELF.cpp
MCELFObjectTargetWriter.cpp
MCELFStreamer.cpp
MCFixup.cpp
MCFunction.cpp
MCExpr.cpp
MCExternalSymbolizer.cpp

14
llvm/lib/MC/ELFObjectWriter.cpp
View File

@ -778,7 +778,7 @@ void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
Index = 0;
}
} else {
if (Asm.getSymbolData(Symbol).getFlags() & ELF_Other_Weakref)
if (Target.getSymA()->getKind() == MCSymbolRefExpr::VK_WEAKREF)
WeakrefUsedInReloc.insert(RelocSymbol);
else
UsedInReloc.insert(RelocSymbol);
@ -823,8 +823,14 @@ ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm,
const MCSymbolData &Data,
bool Used, bool Renamed) {
if (Data.getFlags() & ELF_Other_Weakref)
return false;
const MCSymbol &Symbol = Data.getSymbol();
if (Symbol.isVariable()) {
const MCExpr *Expr = Symbol.getVariableValue();
if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
return false;
}
}
if (Used)
return true;
@ -832,8 +838,6 @@ bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm,
if (Renamed)
return false;
const MCSymbol &Symbol = Data.getSymbol();
if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
return true;

5
llvm/lib/MC/MCELFStreamer.cpp
View File

@ -99,9 +99,8 @@ void MCELFStreamer::ChangeSection(const MCSection *Section,
void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
getAssembler().getOrCreateSymbolData(*Symbol);
MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
const MCExpr *Value = MCSymbolRefExpr::Create(
Symbol, MCSymbolRefExpr::VK_WEAKREF, getContext());
Alias->setVariableValue(Value);
}

33
llvm/lib/MC/MCExpr.cpp
View File

@ -180,6 +180,7 @@ StringRef MCSymbolRefExpr::getVariantKindName(VariantKind Kind) {
case VK_DTPOFF: return "DTPOFF";
case VK_TLVP: return "TLVP";
case VK_SECREL: return "SECREL32";
case VK_WEAKREF: return "WEAKREF";
case VK_ARM_NONE: return "none";
case VK_ARM_TARGET1: return "target1";
case VK_ARM_TARGET2: return "target2";
@ -630,17 +631,31 @@ bool MCExpr::EvaluateAsRelocatableImpl(MCValue &Res,
case SymbolRef: {
const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
const MCSymbol &Sym = SRE->getSymbol();
const MCAsmInfo &MCAsmInfo = SRE->getMCAsmInfo();
// Evaluate recursively if this is a variable.
if (Sym.isVariable() && SRE->getKind() == MCSymbolRefExpr::VK_None) {
bool Ret = Sym.getVariableValue()->EvaluateAsRelocatableImpl(Res, Asm,
Layout,
Addrs,
true);
// If we failed to simplify this to a constant, let the target
// handle it.
if (Ret && !Res.getSymA() && !Res.getSymB())
return true;
if (Sym.isVariable()) {
if (Sym.getVariableValue()->EvaluateAsRelocatableImpl(Res, Asm, Layout,
Addrs, true)) {
const MCSymbolRefExpr *A = Res.getSymA();
const MCSymbolRefExpr *B = Res.getSymB();
if (MCAsmInfo.hasSubsectionsViaSymbols()) {
// FIXME: This is small hack. Given
// a = b + 4
// .long a
// the OS X assembler will completely drop the 4. We should probably
// include it in the relocation or produce an error if that is not
// possible.
if (!A && !B)
return true;
} else {
bool IsSymbol = A && A->getSymbol().isDefined();
bool IsWeakRef = SRE->getKind() == MCSymbolRefExpr::VK_WEAKREF;
if (!IsSymbol && !IsWeakRef)
return true;
}
}
}
Res = MCValue::get(SRE, 0, 0);

36
llvm/lib/MC/MCFixup.cpp Normal file
View File

@ -0,0 +1,36 @@
//===- MCFixup.cpp - Assembly Fixup Implementation ------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCFixup.h"
using namespace llvm;
static MCSymbolRefExpr::VariantKind getAccessVariant(const MCExpr *Expr) {
switch (Expr->getKind()) {
case MCExpr::Unary:
case MCExpr::Target:
llvm_unreachable("unsupported");
case MCExpr::Constant:
return MCSymbolRefExpr::VK_None;
case MCExpr::SymbolRef: {
const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(Expr);
return SRE->getKind();
}
case MCExpr::Binary: {
const MCBinaryExpr *ABE = cast<MCBinaryExpr>(Expr);
assert(getAccessVariant(ABE->getRHS()) == MCSymbolRefExpr::VK_None);
return getAccessVariant(ABE->getLHS());
}
}
}
MCSymbolRefExpr::VariantKind MCFixup::getAccessVariant() const {
return ::getAccessVariant(getValue());
}

12
llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
View File

@ -71,17 +71,16 @@ const MCSymbol *ARMELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
bool InNormalSection = true;
unsigned RelocType = 0;
RelocType = GetRelocTypeInner(Target, Fixup, IsPCRel);
assert(!Target.getSymB() ||
Target.getSymB()->getKind() == MCSymbolRefExpr::VK_None);
DEBUG(
const MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
MCSymbolRefExpr::VariantKind Kind2;
Kind2 = Target.getSymB() ? Target.getSymB()->getKind() :
MCSymbolRefExpr::VK_None;
MCSymbolRefExpr::VariantKind Kind = Fixup.getAccessVariant();
dbgs() << "considering symbol "
<< Section.getSectionName() << "/"
<< Symbol.getName() << "/"
<< " Rel:" << (unsigned)RelocType
<< " Kind: " << (int)Kind << "/" << (int)Kind2
<< " Kind: " << (int)Kind
<< " Tmp:"
<< Symbol.isAbsolute() << "/" << Symbol.isDefined() << "/"
<< Symbol.isVariable() << "/" << Symbol.isTemporary()
@ -152,8 +151,7 @@ unsigned ARMELFObjectWriter::GetRelocType(const MCValue &Target,
unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
const MCFixup &Fixup,
bool IsPCRel) const {
MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ?
MCSymbolRefExpr::VK_None : Target.getSymA()->getKind();
MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
unsigned Type = 0;
if (IsPCRel) {

33
llvm/lib/Target/PowerPC/MCTargetDesc/PPCELFObjectWriter.cpp
View File

@ -9,6 +9,7 @@
#include "MCTargetDesc/PPCMCTargetDesc.h"
#include "MCTargetDesc/PPCFixupKinds.h"
#include "MCTargetDesc/PPCMCExpr.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCExpr.h"
@ -49,12 +50,37 @@ PPCELFObjectWriter::PPCELFObjectWriter(bool Is64Bit, uint8_t OSABI)
PPCELFObjectWriter::~PPCELFObjectWriter() {
}
static MCSymbolRefExpr::VariantKind getAccessVariant(const MCFixup &Fixup) {
const MCExpr *Expr = Fixup.getValue();
if (Expr->getKind() != MCExpr::Target)
return Fixup.getAccessVariant();
switch (cast<PPCMCExpr>(Expr)->getKind()) {
case PPCMCExpr::VK_PPC_None:
return MCSymbolRefExpr::VK_None;
case PPCMCExpr::VK_PPC_LO:
return MCSymbolRefExpr::VK_PPC_LO;
case PPCMCExpr::VK_PPC_HI:
return MCSymbolRefExpr::VK_PPC_HI;
case PPCMCExpr::VK_PPC_HA:
return MCSymbolRefExpr::VK_PPC_HA;
case PPCMCExpr::VK_PPC_HIGHERA:
return MCSymbolRefExpr::VK_PPC_HIGHERA;
case PPCMCExpr::VK_PPC_HIGHER:
return MCSymbolRefExpr::VK_PPC_HIGHER;
case PPCMCExpr::VK_PPC_HIGHEST:
return MCSymbolRefExpr::VK_PPC_HIGHEST;
case PPCMCExpr::VK_PPC_HIGHESTA:
return MCSymbolRefExpr::VK_PPC_HIGHESTA;
}
}
unsigned PPCELFObjectWriter::getRelocTypeInner(const MCValue &Target,
const MCFixup &Fixup,
bool IsPCRel) const
{
MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ?
MCSymbolRefExpr::VK_None : Target.getSymA()->getKind();
MCSymbolRefExpr::VariantKind Modifier = getAccessVariant(Fixup);
// determine the type of the relocation
unsigned Type;
@ -368,8 +394,7 @@ const MCSymbol *PPCELFObjectWriter::ExplicitRelSym(const MCAssembler &Asm,
const MCFixup &Fixup,
bool IsPCRel) const {
assert(Target.getSymA() && "SymA cannot be 0");
MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ?
MCSymbolRefExpr::VK_None : Target.getSymA()->getKind();
MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
bool EmitThisSym;
switch (Modifier) {

4
llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp
View File

@ -88,9 +88,7 @@ unsigned SystemZObjectWriter::GetRelocType(const MCValue &Target,
bool IsPCRel,
bool IsRelocWithSymbol,
int64_t Addend) const {
MCSymbolRefExpr::VariantKind Modifier = (Target.isAbsolute() ?
MCSymbolRefExpr::VK_None :
Target.getSymA()->getKind());
MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
unsigned Kind = Fixup.getKind();
switch (Modifier) {
case MCSymbolRefExpr::VK_None:

3
llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
View File

@ -46,8 +46,7 @@ unsigned X86ELFObjectWriter::GetRelocType(const MCValue &Target,
int64_t Addend) const {
// determine the type of the relocation
MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ?
MCSymbolRefExpr::VK_None : Target.getSymA()->getKind();
MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
unsigned Type;
if (getEMachine() == ELF::EM_X86_64) {
if (IsPCRel) {

4
llvm/test/MC/ELF/relocation.s
View File

@ -25,6 +25,9 @@ bar:
.word foo-bar
.byte foo-bar
zed = foo +2
call zed@PLT
// CHECK: Section {
// CHECK: Name: .rela.text
// CHECK: Relocations [
@ -49,6 +52,7 @@ bar:
// CHECK-NEXT: 0x85 R_X86_64_TPOFF64 baz 0x0
// CHECK-NEXT: 0x8D R_X86_64_PC16 foo 0x8D
// CHECK-NEXT: 0x8F R_X86_64_PC8 foo 0x8F
// CHECK-NEXT: 0x91 R_X86_64_PLT32 foo 0xFFFFFFFFFFFFFFFE
// CHECK-NEXT: ]
// CHECK-NEXT: }

20
llvm/test/MC/X86/reloc-undef-global.s Normal file
View File

@ -0,0 +1,20 @@
// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux %s -o - | llvm-readobj -r | FileCheck --check-prefix=ELF %s
// RUN: llvm-mc -filetype=obj -triple x86_64-apple-darwin %s -o - | llvm-readobj -r | FileCheck --check-prefix=MACHO %s
bar = foo + 4
.globl bar
.long bar
// ELF: Relocations [
// ELF-NEXT: Section (2) .rela.text {
// ELF-NEXT: 0x0 R_X86_64_32 foo 0x4
// ELF-NEXT: }
// ELF-NEXT: ]
// MACHO: Relocations [
// MACHO: Section __text {
// MACHO: 0x0 0 2 1 X86_64_RELOC_UNSIGNED 0 bar
// MACHO: }
// MACHO: ]