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Start adding target abstractions. 

This is just enough to get PLT working on 32 bit x86.

The idea behind using a virtual interface is that it should be easy to
convert any of the functions to template parameters if any turns out to be
performance critical.

llvm-svn: 248308
This commit is contained in:
Rafael Espindola 2015-09-22 18:19:46 +00:00
parent e8fe34d4d1
commit 01205f79a4
10 changed files with 235 additions and 47 deletions
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1
lld/ELF/CMakeLists.txt
View File

@ -11,6 +11,7 @@ add_llvm_library(lldELF2
OutputSections.cpp
SymbolTable.cpp
Symbols.cpp
Target.cpp
Writer.cpp
LINK_COMPONENTS

9
lld/ELF/InputSection.cpp
View File

@ -11,6 +11,7 @@
#include "Error.h"
#include "InputFiles.h"
#include "OutputSections.h"
#include "Target.h"
#include "llvm/Support/raw_ostream.h"
@ -114,12 +115,12 @@ void InputSection<ELFT>::relocate(
break;
}
case SymbolBody::SharedKind:
if (relocNeedsPLT(Type)) {
if (Target->relocNeedsPlt(Type)) {
SymVA = PltSec.getEntryAddr(*Body);
Type = R_X86_64_PC32;
} else if (relocNeedsGOT(Type)) {
Type = Target->getPCRelReloc();
} else if (Target->relocNeedsGot(Type)) {
SymVA = GotSec.getEntryAddr(*Body);
Type = R_X86_64_PC32;
Type = Target->getPCRelReloc();
} else {
continue;
}

41
lld/ELF/OutputSections.cpp
View File

@ -10,6 +10,7 @@
#include "OutputSections.h"
#include "Config.h"
#include "SymbolTable.h"
#include "Target.h"
using namespace llvm;
using namespace llvm::object;
@ -42,21 +43,11 @@ template <class ELFT> void PltSection<ELFT>::writeTo(uint8_t *Buf) {
uintptr_t Start = reinterpret_cast<uintptr_t>(Buf);
ArrayRef<uint8_t> Jmp = {0xff, 0x25}; // jmpq *val(%rip)
for (const SymbolBody *E : Entries) {
uint64_t GotEntryAddr = GotSec.getEntryAddr(*E);
uintptr_t InstPos = reinterpret_cast<uintptr_t>(Buf);
memcpy(Buf, Jmp.data(), Jmp.size());
Buf += Jmp.size();
uintptr_t OffsetInPLT = (InstPos + 6) - Start;
intptr_t Delta = GotSec.getEntryAddr(*E) - (this->getVA() + OffsetInPLT);
assert(isInt<32>(Delta));
support::endian::write32le(Buf, Delta);
Buf += 4;
*Buf = 0x90; // nop
++Buf;
*Buf = 0x90; // nop
++Buf;
uint64_t PltEntryAddr = (InstPos - Start) + this->getVA();
Target->writePltEntry(Buf, GotEntryAddr, PltEntryAddr);
Buf += 8;
}
}
@ -71,26 +62,6 @@ PltSection<ELFT>::getEntryAddr(const SymbolBody &B) const {
return this->getVA() + B.getPltIndex() * EntrySize;
}
bool lld::elf2::relocNeedsPLT(uint32_t Type) {
switch (Type) {
default:
return false;
case R_X86_64_PLT32:
return true;
}
}
bool lld::elf2::relocNeedsGOT(uint32_t Type) {
if (relocNeedsPLT(Type))
return true;
switch (Type) {
default:
return false;
case R_X86_64_GOTPCREL:
return true;
}
}
template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *Buf) {
const unsigned EntrySize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
bool IsMips64EL = Relocs[0].C.getFile()->getObj()->isMips64EL();
@ -104,7 +75,7 @@ template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *Buf) {
uint32_t SymIndex = RI.getSymbol(IsMips64EL);
const SymbolBody *Body = C.getFile()->getSymbolBody(SymIndex);
uint32_t Type = RI.getType(IsMips64EL);
if (relocNeedsGOT(Type)) {
if (Target->relocNeedsGot(Type)) {
P->r_offset = GotSec.getEntryAddr(*Body);
P->setSymbolAndType(Body->getDynamicSymbolTableIndex(), R_X86_64_GLOB_DAT,
IsMips64EL);

3
lld/ELF/OutputSections.h
View File

@ -29,9 +29,6 @@ template <class ELFT> class OutputSection;
template <class ELFT> class ObjectFile;
template <class ELFT> class DefinedRegular;
bool relocNeedsPLT(uint32_t Type);
bool relocNeedsGOT(uint32_t Type);
template <class ELFT>
typename llvm::object::ELFFile<ELFT>::uintX_t
getSymVA(const DefinedRegular<ELFT> *DR);

10
lld/ELF/SymbolTable.cpp
View File

@ -11,9 +11,11 @@
#include "Config.h"
#include "Error.h"
#include "Symbols.h"
#include "Target.h"
using namespace llvm;
using namespace llvm::object;
using namespace llvm::ELF;
using namespace lld;
using namespace lld::elf2;
@ -37,7 +39,11 @@ void SymbolTable::addFile(std::unique_ptr<InputFile> File) {
addELFFile(cast<ELFFileBase>(FileP));
}
template <class ELFT> void SymbolTable::init() {
template <class ELFT> void SymbolTable::init(uint16_t EMachine) {
if (EMachine == EM_X86_64)
Target.reset(new X86_64TargetInfo());
else
Target.reset(new X86TargetInfo());
if (Config->Shared)
return;
EntrySym = new (Alloc) Undefined<ELFT>("_start", Undefined<ELFT>::Synthetic);
@ -49,7 +55,7 @@ template <class ELFT> void SymbolTable::addELFFile(ELFFileBase *File) {
if (!Old->isCompatibleWith(*File))
error(Twine(Old->getName() + " is incompatible with " + File->getName()));
} else {
init<ELFT>();
init<ELFT>(File->getEMachine());
}
if (auto *O = dyn_cast<ObjectFileBase>(File)) {

2
lld/ELF/SymbolTable.h
View File

@ -68,7 +68,7 @@ private:
void addLazy(Lazy *New);
void addMemberFile(Lazy *Body);
template <class ELFT> void init();
template <class ELFT> void init(uint16_t EMachine);
template <class ELFT> void resolve(SymbolBody *Body);
std::vector<std::unique_ptr<ArchiveFile>> ArchiveFiles;

100
lld/ELF/Target.cpp Normal file
View File

@ -0,0 +1,100 @@
//===- Target.cpp ---------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "Target.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/ELF.h"
using namespace llvm;
using namespace llvm::ELF;
namespace lld {
namespace elf2 {
std::unique_ptr<TargetInfo> Target;
TargetInfo::~TargetInfo() {}
X86TargetInfo::X86TargetInfo() { PCRelReloc = R_386_PC32; }
void X86TargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
uint64_t PltEntryAddr) const {
ArrayRef<uint8_t> Jmp = {0xff, 0x25}; // jmpl *val
memcpy(Buf, Jmp.data(), Jmp.size());
Buf += Jmp.size();
assert(isUInt<32>(GotEntryAddr));
support::endian::write32le(Buf, GotEntryAddr);
Buf += 4;
ArrayRef<uint8_t> Nops = {0x90, 0x90};
memcpy(Buf, Nops.data(), Nops.size());
}
bool X86TargetInfo::relocNeedsGot(uint32_t Type) const {
if (relocNeedsPlt(Type))
return true;
switch (Type) {
default:
return false;
case R_386_GOT32:
return true;
}
}
bool X86TargetInfo::relocNeedsPlt(uint32_t Type) const {
switch (Type) {
default:
return false;
case R_386_PLT32:
return true;
}
}
X86_64TargetInfo::X86_64TargetInfo() { PCRelReloc = R_X86_64_PC32; }
void X86_64TargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
uint64_t PltEntryAddr) const {
ArrayRef<uint8_t> Jmp = {0xff, 0x25}; // jmpq *val(%rip)
memcpy(Buf, Jmp.data(), Jmp.size());
Buf += Jmp.size();
uintptr_t NextPC = PltEntryAddr + 6;
uintptr_t Delta = GotEntryAddr - NextPC;
assert(isInt<32>(Delta));
support::endian::write32le(Buf, Delta);
Buf += 4;
ArrayRef<uint8_t> Nops = {0x90, 0x90};
memcpy(Buf, Nops.data(), Nops.size());
}
bool X86_64TargetInfo::relocNeedsGot(uint32_t Type) const {
if (relocNeedsPlt(Type))
return true;
switch (Type) {
default:
return false;
case R_X86_64_GOTPCREL:
return true;
}
}
bool X86_64TargetInfo::relocNeedsPlt(uint32_t Type) const {
switch (Type) {
default:
return false;
case R_X86_64_PLT32:
return true;
}
}
}
}

54
lld/ELF/Target.h Normal file
View File

@ -0,0 +1,54 @@
//===- Target.h -------------------------------------------------*- C++ -*-===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef LLD_ELF_TARGET_H
#define LLD_ELF_TARGET_H
#include <memory>
namespace lld {
namespace elf2 {
class SymbolBody;
class TargetInfo {
public:
unsigned getPCRelReloc() const { return PCRelReloc; }
virtual void writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
uint64_t PltEntryAddr) const = 0;
virtual bool relocNeedsGot(uint32_t Type) const = 0;
virtual bool relocNeedsPlt(uint32_t Type) const = 0;
virtual ~TargetInfo();
protected:
unsigned PCRelReloc;
};
class X86TargetInfo final : public TargetInfo {
public:
X86TargetInfo();
void writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
uint64_t PltEntryAddr) const override;
bool relocNeedsGot(uint32_t Type) const override;
bool relocNeedsPlt(uint32_t Type) const override;
};
class X86_64TargetInfo final : public TargetInfo {
public:
X86_64TargetInfo();
void writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
uint64_t PltEntryAddr) const override;
bool relocNeedsGot(uint32_t Type) const override;
bool relocNeedsPlt(uint32_t Type) const override;
};
extern std::unique_ptr<TargetInfo> Target;
}
}
#endif

5
lld/ELF/Writer.cpp
View File

@ -11,6 +11,7 @@
#include "Config.h"
#include "OutputSections.h"
#include "SymbolTable.h"
#include "Target.h"
#include "llvm/Support/FileOutputBuffer.h"
@ -256,12 +257,12 @@ void Writer<ELFT>::scanRelocs(
if (!S)
continue;
uint32_t Type = RI.getType(IsMips64EL);
if (relocNeedsPLT(Type)) {
if (Target->relocNeedsPlt(Type)) {
if (Body->isInPlt())
continue;
PltSec.addEntry(Body);
}
if (relocNeedsGOT(Type)) {
if (Target->relocNeedsGot(Type)) {
if (Body->isInGot())
continue;
GotSec.addEntry(Body);

57
lld/test/elf2/plt-i686.s Normal file
View File

@ -0,0 +1,57 @@
// RUN: llvm-mc -filetype=obj -triple=i686-unknown-linux %s -o %t.o
// RUN: llvm-mc -filetype=obj -triple=i686-unknown-linux %p/Inputs/shared.s -o %t2.o
// RUN: lld -flavor gnu2 -shared %t2.o -o %t2.so
// RUN: lld -flavor gnu2 %t.o %t2.so -o %t
// RUN: llvm-readobj -s -r %t | FileCheck %s
// RUN: llvm-objdump -d %t | FileCheck --check-prefix=DISASM %s
// REQUIRES: x86
// CHECK: Name: .plt
// CHECK-NEXT: Type: SHT_PROGBITS
// CHECK-NEXT: Flags [
// CHECK-NEXT: SHF_ALLOC
// CHECK-NEXT: SHF_EXECINSTR
// CHECK-NEXT: ]
// CHECK-NEXT: Address: 0x16000
// CHECK-NEXT: Offset:
// CHECK-NEXT: Size: 16
// CHECK-NEXT: Link: 0
// CHECK-NEXT: Info: 0
// CHECK-NEXT: AddressAlignment: 16
// CHECK: Relocations [
// CHECK-NEXT: Section ({{.*}}) .rel.dyn {
// CHECK-NEXT: 0x15000 R_386_GLOB_DAT bar 0x0
// CHECK-NEXT: 0x15004 R_386_GLOB_DAT zed 0x0
// CHECK-NEXT: }
// CHECK-NEXT: ]
// Unfortunately FileCheck can't do math, so we have to check for explicit
// values:
// 0x16000 - (0x11000 + 1) - 4 = 20475
// 0x16000 - (0x11005 + 1) - 4 = 20470
// 0x16008 - (0x1100a + 1) - 4 = 20473
// DISASM: _start:
// DISASM-NEXT: 11000: e9 fb 4f 00 00 jmp 20475
// DISASM-NEXT: 11005: e9 f6 4f 00 00 jmp 20470
// DISASM-NEXT: 1100a: e9 f9 4f 00 00 jmp 20473
// 0x15000 = 86016
// 0x15004 = 86020
// DISASM: Disassembly of section .plt:
// DISASM-NEXT: .plt:
// DISASM-NEXT: 16000: ff 25 00 50 01 00 jmpl *86016
// DISASM-NEXT: 16006: 90 nop
// DISASM-NEXT: 16007: 90 nop
// DISASM-NEXT: 16008: ff 25 04 50 01 00 jmpl *86020
// DISASM-NEXT: 1600e: 90 nop
// DISASM-NEXT: 1600f: 90 nop
.global _start
_start:
jmp bar@PLT
jmp bar@PLT
jmp zed@PLT