6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-11-23 00:20:25 +00:00
Code Issues Projects Releases Wiki Activity

Remove doesSectionRequireSymbols.

Browse Source 
In an assembly expression like

bar:
.long L0 + 1

the intended semantics is that bar will contain a pointer one byte past L0.

In sections that are merged by content (strings, 4 byte constants, etc), a
single position in the section doesn't give the linker enough information.
For example, it would not be able to tell a relocation must point to the
end of a string, since that would look just like the start of the next.

The solution used in ELF to use relocation with symbols if there is a non-zero
addend.

In MachO before this patch we would just keep all symbols in some sections.

This would miss some cases (only cstrings on x86_64 were implemented) and was
inefficient since most relocations have an addend of 0 and can be represented
without the symbol.

This patch implements the non-zero addend logic for MachO too.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224985 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola
2014-12-30 13:13:27 +00:00
parent 96341cbb36
commit 65300b95e6
19 changed files with 293 additions and 241 deletions
Download Patch File Download Diff File Expand all files Collapse all files

114
lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp
View File

@@ -10,6 +10,7 @@
#include "MCTargetDesc/X86MCTargetDesc.h"
#include "MCTargetDesc/X86FixupKinds.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
@@ -47,23 +48,21 @@ class X86MachObjectWriter : public MCMachObjectTargetWriter {
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue);
void RecordX86_64Relocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
void RecordX86_64Relocation(MachObjectWriter *Writer, MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue);
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, uint64_t &FixedValue);
public:
X86MachObjectWriter(bool Is64Bit, uint32_t CPUType,
uint32_t CPUSubtype)
: MCMachObjectTargetWriter(Is64Bit, CPUType, CPUSubtype,
/*UseAggressiveSymbolFolding=*/Is64Bit) {}
void RecordRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, uint64_t &FixedValue) override {
void RecordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
const MCAsmLayout &Layout, const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue) override {
if (Writer->is64Bit())
RecordX86_64Relocation(Writer, Asm, Layout, Fragment, Fixup, Target,
FixedValue);
@@ -97,13 +96,10 @@ static unsigned getFixupKindLog2Size(unsigned Kind) {
}
}
void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue) {
void X86MachObjectWriter::RecordX86_64Relocation(
MachObjectWriter *Writer, MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
unsigned IsRIPRel = isFixupKindRIPRel(Fixup.getKind());
unsigned Log2Size = getFixupKindLog2Size(Fixup.getKind());
@@ -117,6 +113,7 @@ void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
unsigned Index = 0;
unsigned IsExtern = 0;
unsigned Type = 0;
const MCSymbolData *RelSymbol = nullptr;
Value = Target.getConstant();
@@ -132,7 +129,6 @@ void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
if (Target.isAbsolute()) { // constant
// SymbolNum of 0 indicates the absolute section.
Type = MachO::X86_64_RELOC_UNSIGNED;
Index = 0;
// FIXME: I believe this is broken, I don't think the linker can understand
// it. I think it would require a local relocation, but I'm not sure if that
@@ -193,36 +189,30 @@ void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
Value -= Writer->getSymbolAddress(&B_SD, Layout) -
(!B_Base ? 0 : Writer->getSymbolAddress(B_Base, Layout));
if (A_Base) {
Index = A_Base->getIndex();
IsExtern = 1;
} else {
if (!A_Base)
Index = A_SD.getFragment()->getParent()->getOrdinal() + 1;
IsExtern = 0;
}
Type = MachO::X86_64_RELOC_UNSIGNED;
MachO::any_relocation_info MRE;
MRE.r_word0 = FixupOffset;
MRE.r_word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Writer->addRelocation(Fragment->getParent(), MRE);
MRE.r_word1 =
(Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
Writer->addRelocation(A_Base, Fragment->getParent(), MRE);
if (B_Base) {
Index = B_Base->getIndex();
IsExtern = 1;
} else {
if (B_Base)
RelSymbol = B_Base;
else
Index = B_SD.getFragment()->getParent()->getOrdinal() + 1;
IsExtern = 0;
}
Type = MachO::X86_64_RELOC_SUBTRACTOR;
} else {
const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
if (Symbol->isTemporary() && Value) {
const MCSection &Sec = Symbol->getSection();
if (!Asm.getContext().getAsmInfo()->isSectionAtomizableBySymbols(Sec))
Asm.addLocalUsedInReloc(*Symbol);
}
const MCSymbolData &SD = Asm.getSymbolData(*Symbol);
const MCSymbolData *Base = Asm.getAtom(&SD);
RelSymbol = Asm.getAtom(&SD);
// Relocations inside debug sections always use local relocations when
// possible. This seems to be done because the debugger doesn't fully
@@ -232,23 +222,20 @@ void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
const MCSectionMachO &Section = static_cast<const MCSectionMachO&>(
Fragment->getParent()->getSection());
if (Section.hasAttribute(MachO::S_ATTR_DEBUG))
Base = nullptr;
RelSymbol = nullptr;
}
// x86_64 almost always uses external relocations, except when there is no
// symbol to use as a base address (a local symbol with no preceding
// non-local symbol).
if (Base) {
Index = Base->getIndex();
IsExtern = 1;
if (RelSymbol) {
// Add the local offset, if needed.
if (Base != &SD)
Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base);
if (RelSymbol != &SD)
Value +=
Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(RelSymbol);
} else if (Symbol->isInSection() && !Symbol->isVariable()) {
// The index is the section ordinal (1-based).
Index = SD.getFragment()->getParent()->getOrdinal() + 1;
IsExtern = 0;
Value += Writer->getSymbolAddress(&SD, Layout);
if (IsPCRel)
@@ -347,12 +334,9 @@ void X86MachObjectWriter::RecordX86_64Relocation(MachObjectWriter *Writer,
// struct relocation_info (8 bytes)
MachO::any_relocation_info MRE;
MRE.r_word0 = FixupOffset;
MRE.r_word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Writer->addRelocation(Fragment->getParent(), MRE);
MRE.r_word1 = (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
(IsExtern << 27) | (Type << 28);
Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
}
bool X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
@@ -424,7 +408,7 @@ bool X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
(IsPCRel << 30) |
MachO::R_SCATTERED);
MRE.r_word1 = Value2;
Writer->addRelocation(Fragment->getParent(), MRE);
Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
} else {
// If the offset is more than 24-bits, it won't fit in a scattered
// relocation offset field, so we fall back to using a non-scattered
@@ -446,7 +430,7 @@ bool X86MachObjectWriter::RecordScatteredRelocation(MachObjectWriter *Writer,
(IsPCRel << 30) |
MachO::R_SCATTERED);
MRE.r_word1 = Value;
Writer->addRelocation(Fragment->getParent(), MRE);
Writer->addRelocation(nullptr, Fragment->getParent(), MRE);
return true;
}
@@ -467,7 +451,6 @@ void X86MachObjectWriter::RecordTLVPRelocation(MachObjectWriter *Writer,
// Get the symbol data.
const MCSymbolData *SD_A = &Asm.getSymbolData(Target.getSymA()->getSymbol());
unsigned Index = SD_A->getIndex();
// We're only going to have a second symbol in pic mode and it'll be a
// subtraction from the picbase. For 32-bit pic the addend is the difference
@@ -490,12 +473,9 @@ void X86MachObjectWriter::RecordTLVPRelocation(MachObjectWriter *Writer,
// struct relocation_info (8 bytes)
MachO::any_relocation_info MRE;
MRE.r_word0 = Value;
MRE.r_word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(1 << 27) | // r_extern
(MachO::GENERIC_RELOC_TLV << 28)); // r_type
Writer->addRelocation(Fragment->getParent(), MRE);
MRE.r_word1 =
(IsPCRel << 24) | (Log2Size << 25) | (MachO::GENERIC_RELOC_TLV << 28);
Writer->addRelocation(SD_A, Fragment->getParent(), MRE);
}
void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
@@ -546,8 +526,8 @@ void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
// See <reloc.h>.
uint32_t FixupOffset = Layout.getFragmentOffset(Fragment)+Fixup.getOffset();
unsigned Index = 0;
unsigned IsExtern = 0;
unsigned Type = 0;
const MCSymbolData *RelSymbol = nullptr;
if (Target.isAbsolute()) { // constant
// SymbolNum of 0 indicates the absolute section.
@@ -568,8 +548,7 @@ void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
// Check whether we need an external or internal relocation.
if (Writer->doesSymbolRequireExternRelocation(SD)) {
IsExtern = 1;
Index = SD->getIndex();
RelSymbol = SD;
// For external relocations, make sure to offset the fixup value to
// compensate for the addend of the symbol address, if it was
// undefined. This occurs with weak definitions, for example.
@@ -591,12 +570,9 @@ void X86MachObjectWriter::RecordX86Relocation(MachObjectWriter *Writer,
// struct relocation_info (8 bytes)
MachO::any_relocation_info MRE;
MRE.r_word0 = FixupOffset;
MRE.r_word1 = ((Index << 0) |
(IsPCRel << 24) |
(Log2Size << 25) |
(IsExtern << 27) |
(Type << 28));
Writer->addRelocation(Fragment->getParent(), MRE);
MRE.r_word1 =
(Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28);
Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE);
}
MCObjectWriter *llvm::createX86MachObjectWriter(raw_ostream &OS,