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llvm-for-llvmta/lib/ExecutionEngine/JITLink/MachOLinkGraphBuilder.cpp

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//=--------- MachOLinkGraphBuilder.cpp - MachO LinkGraph builder ----------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Generic MachO LinkGraph buliding code.
//
//===----------------------------------------------------------------------===//
#include "MachOLinkGraphBuilder.h"
#define DEBUG_TYPE "jitlink"
static const char *CommonSectionName = "__common";
namespace llvm {
namespace jitlink {
MachOLinkGraphBuilder::~MachOLinkGraphBuilder() {}
Expected<std::unique_ptr<LinkGraph>> MachOLinkGraphBuilder::buildGraph() {
// Sanity check: we only operate on relocatable objects.
if (!Obj.isRelocatableObject())
return make_error<JITLinkError>("Object is not a relocatable MachO");
if (auto Err = createNormalizedSections())
return std::move(Err);
if (auto Err = createNormalizedSymbols())
return std::move(Err);
if (auto Err = graphifyRegularSymbols())
return std::move(Err);
if (auto Err = graphifySectionsWithCustomParsers())
return std::move(Err);
if (auto Err = addRelocations())
return std::move(Err);
return std::move(G);
}
MachOLinkGraphBuilder::MachOLinkGraphBuilder(const object::MachOObjectFile &Obj,
Triple TT)
: Obj(Obj),
G(std::make_unique<LinkGraph>(std::string(Obj.getFileName()),
std::move(TT), getPointerSize(Obj),
getEndianness(Obj))) {}
void MachOLinkGraphBuilder::addCustomSectionParser(
StringRef SectionName, SectionParserFunction Parser) {
assert(!CustomSectionParserFunctions.count(SectionName) &&
"Custom parser for this section already exists");
CustomSectionParserFunctions[SectionName] = std::move(Parser);
}
Linkage MachOLinkGraphBuilder::getLinkage(uint16_t Desc) {
if ((Desc & MachO::N_WEAK_DEF) || (Desc & MachO::N_WEAK_REF))
return Linkage::Weak;
return Linkage::Strong;
}
Scope MachOLinkGraphBuilder::getScope(StringRef Name, uint8_t Type) {
if (Type & MachO::N_EXT) {
if ((Type & MachO::N_PEXT) || Name.startswith("l"))
return Scope::Hidden;
else
return Scope::Default;
}
return Scope::Local;
}
bool MachOLinkGraphBuilder::isAltEntry(const NormalizedSymbol &NSym) {
return NSym.Desc & MachO::N_ALT_ENTRY;
}
bool MachOLinkGraphBuilder::isDebugSection(const NormalizedSection &NSec) {
return (NSec.Flags & MachO::S_ATTR_DEBUG &&
strcmp(NSec.SegName, "__DWARF") == 0);
}
unsigned
MachOLinkGraphBuilder::getPointerSize(const object::MachOObjectFile &Obj) {
return Obj.is64Bit() ? 8 : 4;
}
support::endianness
MachOLinkGraphBuilder::getEndianness(const object::MachOObjectFile &Obj) {
return Obj.isLittleEndian() ? support::little : support::big;
}
Section &MachOLinkGraphBuilder::getCommonSection() {
if (!CommonSection) {
auto Prot = static_cast<sys::Memory::ProtectionFlags>(
sys::Memory::MF_READ | sys::Memory::MF_WRITE);
CommonSection = &G->createSection(CommonSectionName, Prot);
}
return *CommonSection;
}
Error MachOLinkGraphBuilder::createNormalizedSections() {
// Build normalized sections. Verifies that section data is in-range (for
// sections with content) and that address ranges are non-overlapping.
LLVM_DEBUG(dbgs() << "Creating normalized sections...\n");
for (auto &SecRef : Obj.sections()) {
NormalizedSection NSec;
uint32_t DataOffset = 0;
auto SecIndex = Obj.getSectionIndex(SecRef.getRawDataRefImpl());
auto Name = SecRef.getName();
if (!Name)
return Name.takeError();
if (Obj.is64Bit()) {
const MachO::section_64 &Sec64 =
Obj.getSection64(SecRef.getRawDataRefImpl());
memcpy(&NSec.SectName, &Sec64.sectname, 16);
NSec.SectName[16] = '\0';
memcpy(&NSec.SegName, Sec64.segname, 16);
NSec.SegName[16] = '\0';
NSec.Address = Sec64.addr;
NSec.Size = Sec64.size;
NSec.Alignment = 1ULL << Sec64.align;
NSec.Flags = Sec64.flags;
DataOffset = Sec64.offset;
} else {
const MachO::section &Sec32 = Obj.getSection(SecRef.getRawDataRefImpl());
memcpy(&NSec.SectName, &Sec32.sectname, 16);
NSec.SectName[16] = '\0';
memcpy(&NSec.SegName, Sec32.segname, 16);
NSec.SegName[16] = '\0';
NSec.Address = Sec32.addr;
NSec.Size = Sec32.size;
NSec.Alignment = 1ULL << Sec32.align;
NSec.Flags = Sec32.flags;
DataOffset = Sec32.offset;
}
LLVM_DEBUG({
dbgs() << " " << *Name << ": " << formatv("{0:x16}", NSec.Address)
<< " -- " << formatv("{0:x16}", NSec.Address + NSec.Size)
<< ", align: " << NSec.Alignment << ", index: " << SecIndex
<< "\n";
});
// Get the section data if any.
{
unsigned SectionType = NSec.Flags & MachO::SECTION_TYPE;
if (SectionType != MachO::S_ZEROFILL &&
SectionType != MachO::S_GB_ZEROFILL) {
if (DataOffset + NSec.Size > Obj.getData().size())
return make_error<JITLinkError>(
"Section data extends past end of file");
NSec.Data = Obj.getData().data() + DataOffset;
}
}
// Get prot flags.
// FIXME: Make sure this test is correct (it's probably missing cases
// as-is).
sys::Memory::ProtectionFlags Prot;
if (NSec.Flags & MachO::S_ATTR_PURE_INSTRUCTIONS)
Prot = static_cast<sys::Memory::ProtectionFlags>(sys::Memory::MF_READ |
sys::Memory::MF_EXEC);
else
Prot = static_cast<sys::Memory::ProtectionFlags>(sys::Memory::MF_READ |
sys::Memory::MF_WRITE);
if (!isDebugSection(NSec))
NSec.GraphSection = &G->createSection(*Name, Prot);
else
LLVM_DEBUG({
dbgs() << " " << *Name
<< " is a debug section: No graph section will be created.\n";
});
IndexToSection.insert(std::make_pair(SecIndex, std::move(NSec)));
}
std::vector<NormalizedSection *> Sections;
Sections.reserve(IndexToSection.size());
for (auto &KV : IndexToSection)
Sections.push_back(&KV.second);
// If we didn't end up creating any sections then bail out. The code below
// assumes that we have at least one section.
if (Sections.empty())
return Error::success();
llvm::sort(Sections,
[](const NormalizedSection *LHS, const NormalizedSection *RHS) {
assert(LHS && RHS && "Null section?");
if (LHS->Address != RHS->Address)
return LHS->Address < RHS->Address;
return LHS->Size < RHS->Size;
});
for (unsigned I = 0, E = Sections.size() - 1; I != E; ++I) {
auto &Cur = *Sections[I];
auto &Next = *Sections[I + 1];
if (Next.Address < Cur.Address + Cur.Size)
return make_error<JITLinkError>(
"Address range for section " +
formatv("\"{0}/{1}\" [ {2:x16} -- {3:x16} ] ", Cur.SegName,
Cur.SectName, Cur.Address, Cur.Address + Cur.Size) +
"overlaps section \"" + Next.SegName + "/" + Next.SectName + "\"" +
formatv("\"{0}/{1}\" [ {2:x16} -- {3:x16} ] ", Next.SegName,
Next.SectName, Next.Address, Next.Address + Next.Size));
}
return Error::success();
}
Error MachOLinkGraphBuilder::createNormalizedSymbols() {
LLVM_DEBUG(dbgs() << "Creating normalized symbols...\n");
for (auto &SymRef : Obj.symbols()) {
unsigned SymbolIndex = Obj.getSymbolIndex(SymRef.getRawDataRefImpl());
uint64_t Value;
uint32_t NStrX;
uint8_t Type;
uint8_t Sect;
uint16_t Desc;
if (Obj.is64Bit()) {
const MachO::nlist_64 &NL64 =
Obj.getSymbol64TableEntry(SymRef.getRawDataRefImpl());
Value = NL64.n_value;
NStrX = NL64.n_strx;
Type = NL64.n_type;
Sect = NL64.n_sect;
Desc = NL64.n_desc;
} else {
const MachO::nlist &NL32 =
Obj.getSymbolTableEntry(SymRef.getRawDataRefImpl());
Value = NL32.n_value;
NStrX = NL32.n_strx;
Type = NL32.n_type;
Sect = NL32.n_sect;
Desc = NL32.n_desc;
}
// Skip stabs.
// FIXME: Are there other symbols we should be skipping?
if (Type & MachO::N_STAB)
continue;
Optional<StringRef> Name;
if (NStrX) {
if (auto NameOrErr = SymRef.getName())
Name = *NameOrErr;
else
return NameOrErr.takeError();
}
LLVM_DEBUG({
dbgs() << " ";
if (!Name)
dbgs() << "<anonymous symbol>";
else
dbgs() << *Name;
dbgs() << ": value = " << formatv("{0:x16}", Value)
<< ", type = " << formatv("{0:x2}", Type)
<< ", desc = " << formatv("{0:x4}", Desc) << ", sect = ";
if (Sect)
dbgs() << static_cast<unsigned>(Sect - 1);
else
dbgs() << "none";
dbgs() << "\n";
});
// If this symbol has a section, sanity check that the addresses line up.
if (Sect != 0) {
auto NSec = findSectionByIndex(Sect - 1);
if (!NSec)
return NSec.takeError();
if (Value < NSec->Address || Value > NSec->Address + NSec->Size)
return make_error<JITLinkError>("Symbol address does not fall within "
"section");
if (!NSec->GraphSection) {
LLVM_DEBUG({
dbgs() << " Skipping: Symbol is in section " << NSec->SegName << "/"
<< NSec->SectName
<< " which has no associated graph section.\n";
});
continue;
}
}
IndexToSymbol[SymbolIndex] =
&createNormalizedSymbol(*Name, Value, Type, Sect, Desc,
getLinkage(Desc), getScope(*Name, Type));
}
return Error::success();
}
void MachOLinkGraphBuilder::addSectionStartSymAndBlock(
Section &GraphSec, uint64_t Address, const char *Data, uint64_t Size,
uint32_t Alignment, bool IsLive) {
Block &B =
Data ? G->createContentBlock(GraphSec, StringRef(Data, Size), Address,
Alignment, 0)
: G->createZeroFillBlock(GraphSec, Size, Address, Alignment, 0);
auto &Sym = G->addAnonymousSymbol(B, 0, Size, false, IsLive);
assert(!AddrToCanonicalSymbol.count(Sym.getAddress()) &&
"Anonymous block start symbol clashes with existing symbol address");
AddrToCanonicalSymbol[Sym.getAddress()] = &Sym;
}
Error MachOLinkGraphBuilder::graphifyRegularSymbols() {
LLVM_DEBUG(dbgs() << "Creating graph symbols...\n");
/// We only have 256 section indexes: Use a vector rather than a map.
std::vector<std::vector<NormalizedSymbol *>> SecIndexToSymbols;
SecIndexToSymbols.resize(256);
// Create commons, externs, and absolutes, and partition all other symbols by
// section.
for (auto &KV : IndexToSymbol) {
auto &NSym = *KV.second;
switch (NSym.Type & MachO::N_TYPE) {
case MachO::N_UNDF:
if (NSym.Value) {
if (!NSym.Name)
return make_error<JITLinkError>("Anonymous common symbol at index " +
Twine(KV.first));
NSym.GraphSymbol = &G->addCommonSymbol(
*NSym.Name, NSym.S, getCommonSection(), 0, NSym.Value,
1ull << MachO::GET_COMM_ALIGN(NSym.Desc),
NSym.Desc & MachO::N_NO_DEAD_STRIP);
} else {
if (!NSym.Name)
return make_error<JITLinkError>("Anonymous external symbol at "
"index " +
Twine(KV.first));
NSym.GraphSymbol = &G->addExternalSymbol(
*NSym.Name, 0,
NSym.Desc & MachO::N_WEAK_REF ? Linkage::Weak : Linkage::Strong);
}
break;
case MachO::N_ABS:
if (!NSym.Name)
return make_error<JITLinkError>("Anonymous absolute symbol at index " +
Twine(KV.first));
NSym.GraphSymbol = &G->addAbsoluteSymbol(
*NSym.Name, NSym.Value, 0, Linkage::Strong, Scope::Default,
NSym.Desc & MachO::N_NO_DEAD_STRIP);
break;
case MachO::N_SECT:
SecIndexToSymbols[NSym.Sect - 1].push_back(&NSym);
break;
case MachO::N_PBUD:
return make_error<JITLinkError>(
"Unupported N_PBUD symbol " +
(NSym.Name ? ("\"" + *NSym.Name + "\"") : Twine("<anon>")) +
" at index " + Twine(KV.first));
case MachO::N_INDR:
return make_error<JITLinkError>(
"Unupported N_INDR symbol " +
(NSym.Name ? ("\"" + *NSym.Name + "\"") : Twine("<anon>")) +
" at index " + Twine(KV.first));
default:
return make_error<JITLinkError>(
"Unrecognized symbol type " + Twine(NSym.Type & MachO::N_TYPE) +
" for symbol " +
(NSym.Name ? ("\"" + *NSym.Name + "\"") : Twine("<anon>")) +
" at index " + Twine(KV.first));
}
}
// Loop over sections performing regular graphification for those that
// don't have custom parsers.
for (auto &KV : IndexToSection) {
auto SecIndex = KV.first;
auto &NSec = KV.second;
if (!NSec.GraphSection) {
LLVM_DEBUG({
dbgs() << " " << NSec.SegName << "/" << NSec.SectName
<< " has no graph section. Skipping.\n";
});
continue;
}
// Skip sections with custom parsers.
if (CustomSectionParserFunctions.count(NSec.GraphSection->getName())) {
LLVM_DEBUG({
dbgs() << " Skipping section " << NSec.GraphSection->getName()
<< " as it has a custom parser.\n";
});
continue;
} else
LLVM_DEBUG({
dbgs() << " Processing section " << NSec.GraphSection->getName()
<< "...\n";
});
bool SectionIsNoDeadStrip = NSec.Flags & MachO::S_ATTR_NO_DEAD_STRIP;
bool SectionIsText = NSec.Flags & MachO::S_ATTR_PURE_INSTRUCTIONS;
auto &SecNSymStack = SecIndexToSymbols[SecIndex];
// If this section is non-empty but there are no symbols covering it then
// create one block and anonymous symbol to cover the entire section.
if (SecNSymStack.empty()) {
if (NSec.Size > 0) {
LLVM_DEBUG({
dbgs() << " Section non-empty, but contains no symbols. "
"Creating anonymous block to cover "
<< formatv("{0:x16}", NSec.Address) << " -- "
<< formatv("{0:x16}", NSec.Address + NSec.Size) << "\n";
});
addSectionStartSymAndBlock(*NSec.GraphSection, NSec.Address, NSec.Data,
NSec.Size, NSec.Alignment,
SectionIsNoDeadStrip);
} else
LLVM_DEBUG({
dbgs() << " Section empty and contains no symbols. Skipping.\n";
});
continue;
}
// Sort the symbol stack in by address, alt-entry status, scope, and name.
// We sort in reverse order so that symbols will be visited in the right
// order when we pop off the stack below.
llvm::sort(SecNSymStack, [](const NormalizedSymbol *LHS,
const NormalizedSymbol *RHS) {
if (LHS->Value != RHS->Value)
return LHS->Value > RHS->Value;
if (isAltEntry(*LHS) != isAltEntry(*RHS))
return isAltEntry(*RHS);
if (LHS->S != RHS->S)
return static_cast<uint8_t>(LHS->S) < static_cast<uint8_t>(RHS->S);
return LHS->Name < RHS->Name;
});
// The first symbol in a section can not be an alt-entry symbol.
if (!SecNSymStack.empty() && isAltEntry(*SecNSymStack.back()))
return make_error<JITLinkError>(
"First symbol in " + NSec.GraphSection->getName() + " is alt-entry");
// If the section is non-empty but there is no symbol covering the start
// address then add an anonymous one.
if (SecNSymStack.back()->Value != NSec.Address) {
auto AnonBlockSize = SecNSymStack.back()->Value - NSec.Address;
LLVM_DEBUG({
dbgs() << " Section start not covered by symbol. "
<< "Creating anonymous block to cover [ "
<< formatv("{0:x16}", NSec.Address) << " -- "
<< formatv("{0:x16}", NSec.Address + AnonBlockSize) << " ]\n";
});
addSectionStartSymAndBlock(*NSec.GraphSection, NSec.Address, NSec.Data,
AnonBlockSize, NSec.Alignment,
SectionIsNoDeadStrip);
}
// Visit section symbols in order by popping off the reverse-sorted stack,
// building blocks for each alt-entry chain and creating symbols as we go.
while (!SecNSymStack.empty()) {
SmallVector<NormalizedSymbol *, 8> BlockSyms;
BlockSyms.push_back(SecNSymStack.back());
SecNSymStack.pop_back();
while (!SecNSymStack.empty() &&
(isAltEntry(*SecNSymStack.back()) ||
SecNSymStack.back()->Value == BlockSyms.back()->Value)) {
BlockSyms.push_back(SecNSymStack.back());
SecNSymStack.pop_back();
}
// BlockNSyms now contains the block symbols in reverse canonical order.
JITTargetAddress BlockStart = BlockSyms.front()->Value;
JITTargetAddress BlockEnd = SecNSymStack.empty()
? NSec.Address + NSec.Size
: SecNSymStack.back()->Value;
JITTargetAddress BlockOffset = BlockStart - NSec.Address;
JITTargetAddress BlockSize = BlockEnd - BlockStart;
LLVM_DEBUG({
dbgs() << " Creating block for " << formatv("{0:x16}", BlockStart)
<< " -- " << formatv("{0:x16}", BlockEnd) << ": "
<< NSec.GraphSection->getName() << " + "
<< formatv("{0:x16}", BlockOffset) << " with "
<< BlockSyms.size() << " symbol(s)...\n";
});
Block &B =
NSec.Data
? G->createContentBlock(
*NSec.GraphSection,
StringRef(NSec.Data + BlockOffset, BlockSize), BlockStart,
NSec.Alignment, BlockStart % NSec.Alignment)
: G->createZeroFillBlock(*NSec.GraphSection, BlockSize,
BlockStart, NSec.Alignment,
BlockStart % NSec.Alignment);
Optional<JITTargetAddress> LastCanonicalAddr;
JITTargetAddress SymEnd = BlockEnd;
while (!BlockSyms.empty()) {
auto &NSym = *BlockSyms.back();
BlockSyms.pop_back();
bool SymLive =
(NSym.Desc & MachO::N_NO_DEAD_STRIP) || SectionIsNoDeadStrip;
LLVM_DEBUG({
dbgs() << " " << formatv("{0:x16}", NSym.Value) << " -- "
<< formatv("{0:x16}", SymEnd) << ": ";
if (!NSym.Name)
dbgs() << "<anonymous symbol>";
else
dbgs() << NSym.Name;
if (SymLive)
dbgs() << " [no-dead-strip]";
if (LastCanonicalAddr == NSym.Value)
dbgs() << " [non-canonical]";
dbgs() << "\n";
});
auto &Sym =
NSym.Name
? G->addDefinedSymbol(B, NSym.Value - BlockStart, *NSym.Name,
SymEnd - NSym.Value, NSym.L, NSym.S,
SectionIsText, SymLive)
: G->addAnonymousSymbol(B, NSym.Value - BlockStart,
SymEnd - NSym.Value, SectionIsText,
SymLive);
NSym.GraphSymbol = &Sym;
if (LastCanonicalAddr != Sym.getAddress()) {
if (LastCanonicalAddr)
SymEnd = *LastCanonicalAddr;
LastCanonicalAddr = Sym.getAddress();
setCanonicalSymbol(Sym);
}
}
}
}
return Error::success();
}
Error MachOLinkGraphBuilder::graphifySectionsWithCustomParsers() {
// Graphify special sections.
for (auto &KV : IndexToSection) {
auto &NSec = KV.second;
// Skip non-graph sections.
if (!NSec.GraphSection)
continue;
auto HI = CustomSectionParserFunctions.find(NSec.GraphSection->getName());
if (HI != CustomSectionParserFunctions.end()) {
auto &Parse = HI->second;
if (auto Err = Parse(NSec))
return Err;
}
}
return Error::success();
}
} // end namespace jitlink
} // end namespace llvm
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