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/*
* Copyright (C) 2025 Igalia, S.L. All rights reserved.
* Copyright 2010 the V8 project authors. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "GdbJIT.h"
#include
#if ENABLE(ASSEMBLER)
#if OS(DARWIN) || OS(LINUX)
#include "CallFrame.h"
#include "CallFrameInlines.h"
#include "Options.h"
#include "ProfilerSupport.h"
#include
#include
#include
#include
#include
#include
WTF_ALLOW_UNSAFE_BUFFER_USAGE_BEGIN
// Binary GDB JIT Interface as described in
// http://sourceware.org/gdb/onlinedocs/gdb/Declarations.html
extern "C" {
enum JITAction {
NoAction = 0,
RegisterFunction = 1,
UnregisterFunction = 2
};
struct JITCodeEntry {
JITCodeEntry* next { };
JITCodeEntry* prev { };
uint8_t* symfileAddr { };
uint64_t symfileSize { };
};
struct JITDescriptor {
uint32_t version { };
uint32_t actionFlag { };
JITCodeEntry* relevantEntry { };
JITCodeEntry* firstEntry { };
};
// GDB will place breakpoint into this function.
// To prevent GCC from inlining or removing it we place noinline attribute
// and inline assembler statement inside.
static REFERENCED_FROM_ASM NEVER_INLINE void __jit_debug_register_code()
{
__asm__("");
}
// GDB will inspect contents of this descriptor.
// Static initialization is necessary to prevent GDB from seeing
// uninitialized descriptor.
static REFERENCED_FROM_ASM JITDescriptor __jit_debug_descriptor = { 1, 0, nullptr, nullptr };
} // extern "C"
namespace JSC {
namespace GdbJITInternal {
static constexpr bool verbose = false;
} // namespace GdbJITInternal
WTF_MAKE_TZONE_ALLOCATED_IMPL(GdbJIT);
GdbJIT& GdbJIT::singleton()
{
static LazyNeverDestroyed logger;
static std::once_flag onceKey;
std::call_once(onceKey, [] {
logger.construct();
});
return logger.get();
}
#if OS(DARWIN)
class MachO;
class MachOSection;
using DebugObject = MachO;
using DebugSection = MachOSection;
#else
class ELF;
class ELFSection;
class ELFStringTable;
using DebugObject = ELF;
using DebugSection = ELFSection;
#endif
template
static inline void writeUnalignedValue(uint8_t* p, V value)
{
memcpy(p, &value, sizeof(V));
}
class Writer : public RefCountedAndCanMakeWeakPtr {
public:
static Ref NODELETE create(DebugObject* obj)
{
return adoptRef(*new Writer(obj));
}
uintptr_t NODELETE position() const { return m_position; }
template
class Slot {
public:
Slot(WeakPtr writer, uintptr_t offset)
: m_writer(writer)
, m_offset(offset)
{
}
T* operator->() { return m_writer->template rawSlotAt(m_offset); }
T operator*() { return *m_writer->template rawSlotAt(m_offset); }
void set(const T& value)
{
writeUnalignedValue(m_writer->template addressAt(m_offset), value);
}
Slot at(int i) { return Slot(m_writer, m_offset + sizeof(T) * i); }
private:
WeakPtr m_writer;
uintptr_t m_offset;
};
template
void write(const T& val)
{
ensure(m_position + sizeof(T));
writeUnalignedValue(addressAt(m_position), val);
m_position += sizeof(T);
}
template
Slot slotAt(uintptr_t offset) LIFETIME_BOUND
{
ensure(offset + sizeof(T));
return Slot(*this, offset);
}
template
Slot createSlotHere() LIFETIME_BOUND
{
return createSlotsHere(1);
}
template
Slot createSlotsHere(uint32_t count) LIFETIME_BOUND
{
uintptr_t slotPosition = m_position;
m_position += sizeof(T) * count;
ensure(m_position);
return slotAt(slotPosition);
}
void ensure(uintptr_t pos)
{
if (m_buffer.size() < pos)
m_buffer.grow(pos);
}
DebugObject* NODELETE debugObject() { return m_debugObject; }
uint8_t* NODELETE buffer() LIFETIME_BOUND { return &m_buffer[0]; }
void align(uintptr_t align)
{
uintptr_t delta = m_position % align;
if (!delta)
return;
uintptr_t padding = align - delta;
ensure(m_position += padding);
ASSERT(m_position % align == 0);
}
void writeULEB128(uintptr_t value)
{
do {
uint8_t byte = value & 0x7F;
value >>= 7;
if (value)
byte |= 0x80;
write(byte);
} while (value);
}
void writeSLEB128(intptr_t value)
{
bool more = true;
while (more) {
int8_t byte = value & 0x7F;
bool byteSign = byte & 0x40;
value >>= 7;
if ((!value && !byteSign) || (value == -1 && byteSign))
more = false;
else
byte |= 0x80;
write(byte);
}
}
void writeString(const CString& str)
{
for (auto c : str.span())
write(c);
write('\0');
}
private:
template
friend class Slot;
template
uint8_t* NODELETE addressAt(uintptr_t offset) LIFETIME_BOUND
{
ASSERT(offset < m_buffer.size() && offset + sizeof(T) symfileSize = symfileSize;
memcpy(entry->symfileAddr, symfileAddr, symfileSize);
entry->prev = entry->next = nullptr;
return entry;
}
static void registerCodeEntry(JITCodeEntry* entry)
{
entry->next = __jit_debug_descriptor.firstEntry;
if (entry->next)
entry->next->prev = entry;
__jit_debug_descriptor.firstEntry = __jit_debug_descriptor.relevantEntry = entry;
__jit_debug_descriptor.actionFlag = RegisterFunction;
__jit_debug_register_code();
}
static void unregisterCodeEntry(JITCodeEntry* entry)
{
if (entry->prev)
entry->prev->next = entry->next;
else
__jit_debug_descriptor.firstEntry = entry->next;
if (entry->next)
entry->next->prev = entry->prev;
__jit_debug_descriptor.relevantEntry = entry;
__jit_debug_descriptor.actionFlag = UnregisterFunction;
__jit_debug_register_code();
}
template
class DebugSectionBase {
WTF_DEPRECATED_MAKE_FAST_ALLOCATED(DebugSectionBase);
public:
virtual ~DebugSectionBase() = default;
virtual void writeBody(Writer::Slot header, Ref writer)
{
uint64_t start = writer->position();
if (writeBodyInternal(writer)) {
header->offset = static_cast(start);
uint64_t end = writer->position();
header->size = std::max(end - start, static_cast(header->size));
}
}
virtual bool writeBodyInternal(Ref) { return false; }
using Header = THeader;
};
struct MachOSectionHeader {
char sectname[16];
char segname[16];
uint64_t addr;
uint64_t size;
uint32_t offset;
uint32_t align;
uint32_t reloff;
uint32_t nreloc;
uint32_t flags;
uint32_t reserved1;
uint32_t reserved2;
uint32_t reserved3;
} __attribute__((packed,aligned(1)));
class MachOSection : public DebugSectionBase {
public:
enum Type {
Regular = 0x0u,
AttrCoalesced = 0xBu,
AttrSomeInstructions = 0x400u,
AttrDebug = 0x02000000u,
AttrPureInstructions = 0x80000000u
};
MachOSection(const CString& name, const CString& segment, uint32_t align, const void* addr, size_t size, uint32_t flags)
: m_name(name)
, m_segment(segment)
, m_align(align)
, m_addr(addr)
, m_size(size)
, m_flags(flags)
{
if (m_align) {
ASSERT(WTF::isPowerOfTwo(align));
m_align = WTF::fastLog2(align);
}
}
~MachOSection() override = default;
virtual void populateHeader(Writer::Slot header)
{
header->addr = reinterpret_cast(m_addr);
header->size = m_size;
header->offset = 0;
header->align = m_align;
header->reloff = 0;
header->nreloc = 0;
header->flags = m_flags;
header->reserved1 = 0;
header->reserved2 = 0;
header->reserved3 = 0;
memset(header->sectname, 0, sizeof(header->sectname));
memset(header->segname, 0, sizeof(header->segname));
ASSERT(m_name.length() < sizeof(header->sectname));
ASSERT(m_segment.length() < sizeof(header->segname));
strncpy(header->sectname, m_name.data(), sizeof(header->sectname));
strncpy(header->segname, m_segment.data(), sizeof(header->segname));
}
const void* NODELETE addr() const { return m_addr; }
size_t NODELETE size() const { return m_size; }
private:
CString m_name;
CString m_segment;
uint32_t m_align;
const void* m_addr;
size_t m_size;
uint32_t m_flags;
};
struct ELFsectionHeader {
uint32_t name;
uint32_t type;
uintptr_t flags;
const void* address;
uintptr_t offset;
uintptr_t size;
uint32_t link;
uint32_t info;
uintptr_t alignment;
uintptr_t entrySize;
} __attribute__((packed,aligned(1)));
#if OS(LINUX)
class ELFSection : public DebugSectionBase {
public:
enum Type {
TypeNull = 0,
TypeProgBits = 1,
TypeSymTab = 2,
TypeStrTab = 3,
TypeRela = 4,
TypeHash = 5,
TypeDynamic = 6,
TypeNote = 7,
TypeNoBits = 8,
TypeRel = 9,
TypeShLib = 10,
TypeDynSym = 11,
TypeLoProc = 0x70000000,
TypeX86_64Unwind = 0x70000001,
TypeHiProc = 0x7FFFFFFF,
TypeLoUser = 0x80000000,
TypeHiUser = 0xFFFFFFFF
};
enum Flags {
FlagWrite = 1,
FlagAlloc = 2,
FlagExec = 4
};
enum SpecialIndexes {
IndexAbsolute = 0xFFF1
};
ELFSection(const CString& name, Type type, uintptr_t align)
: m_type(type)
, m_name(name)
, m_align(align)
{
}
~ELFSection() override = default;
void populateHeader(Writer::Slot, ELFStringTable* strtab);
void writeBody(Writer::Slot header, Ref writer) override
{
uintptr_t start = writer->position();
if (writeBodyInternal(writer)) {
uintptr_t end = writer->position();
header->offset = start;
header->size = end - start;
}
}
bool writeBodyInternal(Ref) override { return false; }
uint16_t index() const { return m_index; }
void setIndex(uint16_t index) { m_index = index; }
const Type m_type;
protected:
virtual void populateHeader(Writer::Slot header)
{
header->flags = 0;
header->address = 0;
header->offset = 0;
header->size = 0;
header->link = 0;
header->info = 0;
header->entrySize = 0;
}
private:
CString m_name;
uintptr_t m_align;
uint16_t m_index;
};
#endif // OS(LINUX)
#if OS(DARWIN)
class MachOTextSection : public MachOSection {
public:
MachOTextSection(uint32_t align, const void* codeAddr, uintptr_t codeSize)
: MachOSection("__text", "__TEXT", align, codeAddr, codeSize, MachOSection::Regular | MachOSection::AttrSomeInstructions | MachOSection::AttrPureInstructions)
, m_codeAddr(reinterpret_cast(codeAddr))
, m_codeSize(codeSize)
{
}
bool writeBodyInternal(Ref writer) override
{
for (auto* ptr = m_codeAddr; ptr < m_codeAddr + m_codeSize / sizeof(uint64_t); ++ptr)
writer->write(*ptr);
return true;
}
private:
const uint64_t* m_codeAddr;
const size_t m_codeSize;
};
#endif // OS(DARWIN)
#if OS(LINUX)
class FullHeaderELFSection : public ELFSection {
public:
FullHeaderELFSection(const CString& name, Type type, uintptr_t align, const void* addr, uintptr_t offset, uintptr_t size, uintptr_t flags)
: ELFSection(name, type, align)
, m_addr(addr)
, m_offset(offset)
, m_size(size)
, m_flags(flags)
{
}
protected:
void populateHeader(Writer::Slot header) override
{
ELFSection::populateHeader(header);
header->address = m_addr;
header->offset = m_offset;
header->size = m_size;
header->flags = m_flags;
}
private:
const void* m_addr;
uintptr_t m_offset;
uintptr_t m_size;
uintptr_t m_flags;
};
class ELFStringTable : public ELFSection {
public:
explicit ELFStringTable(const CString& name)
: ELFSection(name, TypeStrTab, 1)
, m_writer(nullptr)
, m_offset(0)
, m_size(0)
{
}
uintptr_t add(const CString& str)
{
if (!str.length())
return 0;
uintptr_t offset = m_size;
writeString(str);
return offset;
}
void attachWriter(Ref w)
{
m_writer = w.ptr();
m_offset = m_writer->position();
// First entry in the string table should be an empty string.
writeString("");
}
void detachWriter()
{
m_writer = nullptr;
}
void writeBody(Writer::Slot header, Ref) override
{
ASSERT(!m_writer);
header->offset = m_offset;
header->size = m_size;
}
private:
void writeString(const CString& str)
{
for (auto c : str.span())
m_writer->write(c);
m_writer->write('\0');
m_size += str.length() + 1;
}
RefPtr m_writer;
uintptr_t m_offset;
uintptr_t m_size;
};
void ELFSection::populateHeader(Writer::Slot header, ELFStringTable* strtab)
{
header->name = static_cast(strtab->add(m_name));
header->type = m_type;
header->alignment = m_align;
populateHeader(header);
}
#endif // OS(LINUX)
#if OS(DARWIN)
class MachO {
WTF_DEPRECATED_MAKE_FAST_ALLOCATED(MachO);
public:
size_t addSection(std::unique_ptr section)
{
m_sections.append(WTF::move(section));
return m_sections.size() - 1;
}
void write(Ref w, const CString& name, uintptr_t codeStart, uintptr_t)
{
Writer::Slot header = writeHeader(w);
uintptr_t loadCommandStart = w->position();
Vector segmentCommands;
Vector sectionHeadersForSegments;
for (auto& section : m_sections) {
segmentCommands.append(writeSegmentCommand(w, reinterpret_cast(section->addr()), section->size()));
sectionHeadersForSegments.append(w->createSlotHere());
}
auto symtabCmd = writeSymtabCommand(w, name);
header->sizeOfCommands = static_cast(w->position() - loadCommandStart);
for (unsigned i = 0; i < m_sections.size(); ++i) {
auto segmentCmd = segmentCommands[i];
auto sectionHeader = sectionHeadersForSegments[i];
segmentCmd->fileOff = w->position();
m_sections[i]->populateHeader(sectionHeader);
m_sections[i]->writeBody(sectionHeader, w);
segmentCmd->fileSize = w->position() - segmentCmd->fileOff;
segmentCmd->vmSize = sectionHeader->size;
}
writeNList(w, symtabCmd, codeStart);
writeStringTable(w, name, symtabCmd);
}
private:
struct MachOHeader {
uint32_t magic;
uint32_t cpuType;
uint32_t cpuSubtype;
uint32_t fileType;
uint32_t numCommands;
uint32_t sizeOfCommands;
uint32_t flags;
uint32_t reserved;
} __attribute__((packed,aligned(1)));
struct MachOSegmentCommand {
uint32_t cmd;
uint32_t cmdSize;
char segname[16];
uint64_t vmAddr;
uint64_t vmSize;
uint64_t fileOff;
uint64_t fileSize;
uint32_t maxProt;
uint32_t initProt;
uint32_t numSects;
uint32_t flags;
} __attribute__((packed,aligned(1)));
struct MachOSymtabCommand {
uint32_t cmd;
uint32_t cmdSize;
uint32_t symFileOff;
uint32_t numSyms;
uint32_t strFileOff;
uint32_t stringBytes;
} __attribute__((packed,aligned(1)));
enum MachOLoadCommandCmd {
LCSegment32 = 0x00000001u,
LCSymTab = 0x00000002u,
LCSegment64 = 0x00000019u,
};
enum NListType {
NAbs = 0x2,
NSect = 0xe,
};
enum NListDescription {
ReferenceFlagDefined = 0x2,
};
struct __attribute__((packed)) NList64 {
uint32_t index;
uint8_t type;
uint8_t section;
uint16_t desc;
uint64_t value;
};
Writer::Slot writeHeader(Ref writer)
{
ASSERT(!writer->position());
Writer::Slot header = writer->createSlotHere();
#if CPU(ARM64)
header->magic = 0xFEEDFACFu;
header->cpuType = 0x0000000C | 0x01000000; // ARM | 64-bit ABI
header->cpuSubtype = 0x00000000; // All
header->reserved = 0;
#elif CPU(X86_64)
header->magic = 0xFEEDFACFu;
header->cpuType = 7 | 0x01000000; // i386 | 64-bit ABI
header->cpuSubtype = 3;
header->reserved = 0;
#else
#error Unsupported target architecture.
#endif
header->fileType = 0x1; // MH_OBJECT
header->numCommands = 3;
header->sizeOfCommands = 0;
header->flags = 0;
return header;
}
Writer::Slot writeSegmentCommand(Ref writer, uintptr_t codeStart, uintptr_t codeSize)
{
auto cmd = writer->createSlotHere();
cmd->cmd = LCSegment64;
cmd->vmAddr = codeStart;
cmd->vmSize = codeSize;
cmd->fileOff = 0;
cmd->fileSize = 0;
cmd->maxProt = 7;
cmd->initProt = 7;
cmd->flags = 0;
cmd->numSects = 1;
memset(cmd->segname, 0, 16);
cmd->cmdSize = sizeof(MachOSegmentCommand) + sizeof(MachOSection::Header) * cmd->numSects;
return cmd;
}
Writer::Slot writeSymtabCommand(Ref writer, const CString& name)
{
auto cmd = writer->createSlotHere();
cmd->cmd = LCSymTab;
cmd->symFileOff = 0;
cmd->numSyms = 1;
cmd->strFileOff = 0;
cmd->stringBytes = name.length() + 1;
cmd->cmdSize = sizeof(MachOSymtabCommand);
return cmd;
}
void writeNList(Ref writer, Writer::Slot cmd, uintptr_t codeStart)
{
cmd->symFileOff = writer->position();
auto slot = writer->createSlotHere();
slot->index = 1;
slot->type = NSect;
slot->section = 2;
slot->desc = 0;
slot->value = codeStart;
}
void writeStringTable(Ref writer, const CString& name, Writer::Slot cmd)
{
cmd->strFileOff = writer->position();
writer->write('\0'); // Index 0
for (auto c : name.span())
writer->write(c);
writer->write('\0');
}
Vector m_sections { };
};
#endif // OS(DARWIN)
#if OS(LINUX)
class ELF {
public:
explicit ELF()
{
m_sections.append(WTF::makeUnique("", ELFSection::TypeNull, 0));
m_sections.append(WTF::makeUnique(".shstrtab"));
}
void write(Ref writer)
{
writeHeader(writer);
writeSectionTable(writer);
writeSections(writer);
}
ELFSection* SectionAt(uint32_t index) { return m_sections[index].get(); }
size_t addSection(std::unique_ptr section)
{
section->setIndex(m_sections.size());
m_sections.append(WTF::move(section));
return m_sections.size() - 1;
}
private:
struct ELFHeader {
uint8_t ident[16];
uint16_t type;
uint16_t machine;
uint32_t version;
uintptr_t entry;
uintptr_t phtOffset;
uintptr_t shtOffset;
uint32_t flags;
uint16_t headerSize;
uint16_t phtEntrySize;
uint16_t phtEntryNum;
uint16_t shtEntrySize;
uint16_t shtEntryNum;
uint16_t shtStrTabIndex;
} __attribute__((packed,aligned(1)));
void writeHeader(Ref writer)
{
ASSERT(!writer->position());
Writer::Slot header = writer->createSlotHere();
#if CPU(X86_64) || CPU(ARM64) || CPU(RISCV64)
const uint8_t ident[16] = {
0x7F, 'E', 'L', 'F', 2, 1, 1, 0,
0, 0, 0, 0, 0, 0, 0, 0
};
#else
#error Unsupported target architecture.
#endif
memcpy(header->ident, ident, 16);
header->type = 1;
#if CPU(X86_64)
// Processor identification value for x64 is 62 as defined in
// System V ABI, AMD64 Supplement
// http://www.x86-64.org/documentation/abi.pdf
header->machine = 62;
#elif CPU(ARM64)
// AARCH64
header->machine = 0xB7;
#elif CPU(RISCV64)
// RISC-V 64
header->machine = 0xF3;
#else
#error Unsupported target architecture.
#endif
header->version = 1;
header->entry = 0;
header->phtOffset = 0;
header->shtOffset = sizeof(ELFHeader); // Section table follows header.
header->flags = 0;
header->headerSize = sizeof(ELFHeader);
header->phtEntrySize = 0;
header->phtEntryNum = 0;
header->shtEntrySize = sizeof(ELFSection::Header);
header->shtEntryNum = m_sections.size();
header->shtStrTabIndex = 1;
}
void writeSectionTable(Ref writer)
{
// Section headers table immediately follows file header.
ASSERT(writer->position() == sizeof(ELFHeader));
Writer::Slot headers = writer->createSlotsHere(
static_cast(m_sections.size()));
// String table for section table is the first section.
ELFStringTable* strtab = static_cast(SectionAt(1));
ASSERT(strtab->m_type == ELFSection::TypeStrTab);
strtab->attachWriter(writer);
uint32_t index = 0;
for (auto& section : m_sections) {
section->populateHeader(headers.at(index), strtab);
index++;
}
strtab->detachWriter();
}
void writeSections(Ref writer)
{
Writer::Slot headers = writer->slotAt(sizeof(ELFHeader));
uint32_t index = 0;
for (auto& section : m_sections) {
section->writeBody(headers.at(index), writer);
index++;
}
}
Vector m_sections;
};
class ELFSymbol {
public:
enum Type {
TypeNone = 0,
TypeObject = 1,
TypeFunction = 2,
TypeSection = 3,
TypeFile = 4,
TypeLoProc = 13,
TypeHiProc = 15
};
enum Binding {
BindLocal = 0,
BindGlobal = 1,
BindWeak = 2,
BindLoProc = 13,
BindHiProc = 15
};
ELFSymbol(const CString& name, uintptr_t value, uintptr_t size, Binding binding, Type type, uint16_t section)
: m_name(name)
, m_value(value)
, m_size(size)
, m_info((binding > 4); }
#if CPU(X86_64) || CPU(ARM64) || CPU(RISCV64)
struct SerializedLayout {
SerializedLayout(uint32_t name, uintptr_t value, uintptr_t size, Binding binding, Type type, uint16_t section)
: m_name(name)
, m_info((binding m_name = static_cast(table->add(m_name));
slot->m_value = m_value;
slot->m_size = m_size;
slot->m_info = m_info;
slot->m_other = m_other;
slot->m_section = m_section;
}
private:
CString m_name;
uintptr_t m_value;
uintptr_t m_size;
uint8_t m_info;
uint8_t m_other;
uint16_t m_section;
};
class ELFSymbolTable : public ELFSection {
public:
ELFSymbolTable(const CString& name)
: ELFSection(name, TypeSymTab, sizeof(uintptr_t))
{
}
void writeBody(Writer::Slot header, Ref writer) override
{
writer->align(header->alignment);
size_t totalSymbols = m_locals.size() + m_globals.size() + 1;
header->offset = writer->position();
Writer::Slot symbols = writer->createSlotsHere(
static_cast(totalSymbols));
header->size = writer->position() - header->offset;
// String table for this symbol table should follow it in the section table.
ELFStringTable* strtab = static_cast(writer->debugObject()->SectionAt(index() + 1));
ASSERT(strtab->m_type == ELFSection::TypeStrTab);
strtab->attachWriter(writer);
symbols.at(0).set(ELFSymbol::SerializedLayout(0, 0, 0, ELFSymbol::BindLocal, ELFSymbol::TypeNone, 0));
writeSymbolsList(&m_locals, symbols.at(1), strtab);
writeSymbolsList(&m_globals, symbols.at(static_cast(m_locals.size() + 1)), strtab);
strtab->detachWriter();
}
void add(const ELFSymbol& symbol)
{
if (symbol.binding() == ELFSymbol::BindLocal)
m_locals.append(symbol);
else
m_globals.append(symbol);
}
protected:
void populateHeader(Writer::Slot header) override
{
ELFSection::populateHeader(header);
// We are assuming that string table will follow symbol table.
header->link = index() + 1;
header->info = static_cast(m_locals.size() + 1);
header->entrySize = sizeof(ELFSymbol::SerializedLayout);
}
private:
void writeSymbolsList(const Vector* src,
Writer::Slot dst,
ELFStringTable* strtab)
{
int i = 0;
for (const ELFSymbol& symbol : *src)
symbol.write(dst.at(i++), strtab);
}
Vector m_locals;
Vector m_globals;
};
static void createSymbolsTable(Ref desc, ELF* elf, size_t textSectionIndex)
{
auto symtab = WTF::makeUnique(".symtab");
auto strtab = WTF::makeUnique(".strtab");
symtab->add(ELFSymbol("JSC Code", 0, 0, ELFSymbol::BindLocal,
ELFSymbol::TypeFile, ELFSection::IndexAbsolute));
symtab->add(ELFSymbol(desc->name(), 0, desc->codeSize(),
ELFSymbol::BindGlobal, ELFSymbol::TypeFunction, textSectionIndex));
// Symbol table should be followed by the linked string table.
elf->addSection(WTF::move(symtab));
elf->addSection(WTF::move(strtab));
}
#endif // OS(LINUX)
class UnwindInfoSection : public DebugSection {
public:
explicit UnwindInfoSection(Ref);
bool writeBodyInternal(Ref) override;
int writeCIE(Ref, uint32_t debugSectionStart);
Writer::Slot writeFDE(Ref);
void writeFDEState(Ref);
void WriteLength(Ref, Writer::Slot* lengthSlot, int initialPosition);
private:
const Ref m_desc;
// DWARF3 Specification, Table 7.23
enum CFIInstructions {
AdvanceLoc = 0x40,
Offset = 0x80,
Restore = 0xC0,
Nop = 0x00,
SetLoc = 0x01,
AdvanceLoc1 = 0x02,
AdvanceLoc2 = 0x03,
AdvanceLoc4 = 0x04,
OffsetExtended = 0x05,
RestoreExtended = 0x06,
Undefined = 0x07,
SameValue = 0x08,
Register = 0x09,
RememberState = 0x0A,
RestoreState = 0x0B,
DefCFA = 0x0C,
DefCFARegister = 0x0D,
DefCFAOffset = 0x0E,
DefCFAExpression = 0x0F,
Expression = 0x10,
OffsetExtendedSF = 0x11,
DefCFASF = 0x12,
DefCFAOffsetSF = 0x13,
ValOffset = 0x14,
ValOffsetSF = 0x15,
ValExpression = 0x16
};
// System V ABI, AMD64 Supplement, Version 0.99.5, Figure 3.36
enum RegisterMapping {
// Only the relevant ones have been added to reduce clutter.
#if CPU(X86_64)
RegisterFP = 6,
RegisterLR = 16,
#elif CPU(ARM64)
RegisterFP = 29,
RegisterLR = 30,
#else
RegisterFP = 7,
RegisterLR = 14,
#endif
};
enum CFIConstants : uint32_t {
CIEID = UINT32_MAX,
CIEVersion = 4,
CodeAlignFactor = 1,
DataAlignFactor = 1,
ReturnAddressRegister = RegisterLR
};
};
void UnwindInfoSection::WriteLength(Ref writer, Writer::Slot* lengthSlot, int initialPosition)
{
uint32_t align = (writer->position() - initialPosition) % sizeof(void*);
if (align) {
for (uint32_t i = 0; i < (sizeof(void*) - align); i++)
writer->write(Nop);
}
ASSERT((writer->position() - initialPosition) % sizeof(void*) == 0);
lengthSlot->set(static_cast(writer->position() - initialPosition));
}
UnwindInfoSection::UnwindInfoSection(Ref desc)
#if OS(LINUX)
: ELFSection(".debug_frame", TypeProgBits, 1)
#elif OS(DARWIN)
: MachOSection("__debug_frame", "__TEXT", sizeof(uintptr_t), 0, 0, MachOSection::Regular)
#else
#error "Unsupported platform"
#endif
, m_desc(desc)
{
}
int UnwindInfoSection::writeCIE(Ref writer, uint32_t)
{
auto ciePosition = static_cast(writer->position());
auto cieLengthSlot = writer->createSlotHere();
writer->write(CIEID);
writer->write(CIEVersion);
writer->write(0); // Null augmentation string.
writer->write(sizeof(uintptr_t)); // Address size
writer->write(0); // Segment size
writer->writeULEB128(CodeAlignFactor);
writer->writeSLEB128(DataAlignFactor);
writer->writeULEB128(ReturnAddressRegister);
WriteLength(writer, &cieLengthSlot, ciePosition + sizeof(*cieLengthSlot));
return ciePosition;
}
Writer::Slot UnwindInfoSection::writeFDE(Ref writer)
{
int fdePosition = static_cast(writer->position());
auto fdeLengthSlot = writer->createSlotHere();
auto ciePointerSlot = writer->createSlotHere();
writer->write(reinterpret_cast(m_desc->codeStart()));
writer->write(reinterpret_cast(m_desc->codeSize()));
writeFDEState(writer);
WriteLength(writer, &fdeLengthSlot, fdePosition + sizeof(*fdeLengthSlot));
return ciePointerSlot;
}
// You can read an example unwind section from GCC:
// readelf --debug-dump=frames ./test
// Or:
// llvm-dwarfdump -a "/tmp/jit-8113659Thunk: CallTrampoline.o"
// Also, try adding `log enable lldb unwind` to your .lldbinit if you debug with lldb,
// or `set debug frame on` and `set debug jit on` for gdb.
// https://refspecs.linuxbase.org/elf/x86_64-abi-0.99.pdf
// https://github.com/ARM-software/abi-aa/blob/main/aadwarf64/aadwarf64.rst#dwarf-register-names
// https://dwarfstd.org/doc/DWARF5.pdf
/*
CFA means canonical frame address. These bytecodes define CFA in terms of other registers,
or other registers in terms of CFA.
In the CIE:
DW_CFA_def_cfa: r31 (sp) ofs 0
00000000004007a4 :
4007a4: d100c3ff sub sp, sp, #0x30 (decimal 48)
DW_CFA_def_cfa_offset: 48
4007a8: a9027bfd stp fp, lr, [sp, #32]
4007ac: 910083fd add fp, sp, #0x20
DW_CFA_def_cfa: r29 (fp) ofs 16
DW_CFA_offset: r30 (lr) at cfa-8
DW_CFA_offset: r29 (fp) at cfa-16
DW_CFA_def_cfa: r31 (sp) ofs 48
400840: a9427bfd ldp fp, lr, [sp, #32]
400844: 9100c3ff add sp, sp, #0x30
DW_CFA_def_cfa_offset: 0
DW_CFA_restore: r30 (lr)
DW_CFA_restore: r29 (fp)
400848: d65f03c0 ret
The generated table:
0x4007a4: CFA=WSP
0x4007a8: CFA=WSP+48
0x4007b0: CFA=W29+16: W29=[CFA-16], W30=[CFA-8]
0x400840: CFA=WSP+48: W29=[CFA-16], W30=[CFA-8]
0x400848: CFA=WSP
*/
void UnwindInfoSection::writeFDEState(Ref writer)
{
// The first state, just after the control has been transferred to the the
// function.
// Since we just want simple unwinding to work, we will just use this blanket rule to
// force the unwidner to check fp. It won't be accurate, but it should be good enough for
// basic debugging.
// Consider when we are after these instructions:
// stp fp, lr
// mov fp, sp
// Then:
// CFA = fp (current) + 8
// fp (previous value) = *(CFA - 16); lr / Return Address (saved) = *(CFA - 8);
// Start with a bogus rule. LLDB is off by one some times, and this seemed to fix it for some reason.
writer->write(DefCFASF);
writer->writeULEB128(RegisterFP);
writer->writeSLEB128(0);
writer->write(AdvanceLoc1);
writer->write(4);
writer->write(DefCFASF);
writer->writeULEB128(RegisterFP);
writer->writeSLEB128(static_cast(sizeof(CallerFrameAndPC)));
writer->write(OffsetExtendedSF);
writer->writeULEB128(RegisterLR);
writer->writeSLEB128(-static_cast(sizeof(uintptr_t)));
writer->write(OffsetExtendedSF);
writer->writeULEB128(RegisterFP);
writer->writeSLEB128(-2 * static_cast(sizeof(uintptr_t)));
}
bool UnwindInfoSection::writeBodyInternal(Ref writer)
{
uint32_t debugSectionStart = writer->position();
// This is a throw-away; The CIE must come first for LLDB to be happy, but
// the offset can't be 0 according to the spec / gdb.
writeCIE(writer, debugSectionStart);
auto ciePosition = writeCIE(writer, debugSectionStart);
auto ciePointer = writeFDE(writer);
ciePointer.set(ciePosition - debugSectionStart);
return true;
}
static JITCodeEntry* createELFObject(Ref desc)
{
constexpr int codeAlignment = 4;
#if OS(DARWIN)
MachO machO;
auto writer = Writer::create(&machO);
if constexpr (isARM64())
machO.addSection(WTF::makeUnique(desc));
machO.addSection(WTF::makeUnique(codeAlignment, desc->codeStart(), desc->codeSize()));
machO.write(writer, desc->name(), reinterpret_cast(desc->codeStart()), desc->codeSize());
#else
ELF elf;
auto writer = Writer::create(&elf);
size_t textSectionIndex = elf.addSection(WTF::makeUnique(
".text", ELFSection::TypeNoBits, codeAlignment, desc->codeStart(), 0,
desc->codeSize(), ELFSection::FlagAlloc | ELFSection::FlagExec));
createSymbolsTable(desc, &elf, textSectionIndex);
if constexpr (isARM64())
elf.addSection(WTF::makeUnique(desc));
elf.write(writer);
#endif
return createCodeEntry(writer->buffer(), writer->position());
}
static std::optional
getOverlappingRegions(GdbJITCodeMap& map, const std::span region)
{
if (map.empty())
return std::nullopt;
// Find the first overlapping entry.
// If successful, points to the first element not less than `region`. The
// returned iterator has the key in `first` and the value in `second`.
auto it = map.lower_bound(region);
auto startIt = it;
if (it == map.end()) {
startIt = map.begin();
// Find the first overlapping entry.
for (; startIt != map.end(); ++startIt) {
if (std::to_address(startIt->first.end()) > region.data())
break;
}
} else if (it != map.begin()) {
for (--it; it != map.begin(); --it) {
if (std::to_address(it->first.end()) first.end()) > region.data())
startIt = it;
}
if (startIt == map.end())
return std::nullopt;
// Find the first non-overlapping entry after `region`.
const auto endIt = map.lower_bound({ std::to_address(region.end()), 0 });
// Return a range containing intersecting regions.
if (std::distance(startIt, endIt) < 1)
return std::nullopt; // No overlapping entries.
return { { startIt, endIt } };
}
static void removeJITCodeEntries(GdbJITCodeMap& map, const std::span region)
{
if (auto overlap = getOverlappingRegions(map, region)) {
auto startIt = overlap->first;
auto endIt = overlap->second;
for (auto it = startIt; it != endIt; ++it)
unregisterCodeEntry(it->second);
map.erase(startIt, endIt);
}
}
// Insert the entry into the map and register it with GDB.
static void addJITCodeEntry(GdbJITCodeMap& map, std::span region,
JITCodeEntry* entry, bool shouldDump, const CString& nameHint)
{
static int fileNum = 0;
if (shouldDump) {
StringPrintStream filename;
if (auto* optionalDirectory = Options::jitDumpDirectory())
filename.print(optionalDirectory);
else
filename.print("/tmp");
filename.print("/jit-", getCurrentProcessID(), fileNum++, nameHint, ".o");
auto fd = open(filename.toCString().data(), O_CREAT | O_TRUNC | O_RDWR, 0666);
RELEASE_ASSERT(fd != -1);
auto file = fdopen(fd, "wb");
RELEASE_ASSERT(file);
fwrite(entry->symfileAddr, entry->symfileSize, 1, file);
fflush(file);
dataLogLnIf(GdbJITInternal::verbose, "GDBInfo dumped: ", nameHint, " ", RawPointer(region.data()), "-", RawPointer(std::to_address(region.end())), " ", region.size(), " ", filename.toCString().data());
}
auto result = map.emplace(region, entry);
ASSERT_UNUSED(result, result.second); // Insertion happened.
registerCodeEntry(entry);
}
void GdbJIT::log(const CString& name, MacroAssemblerCodeRef code)
{
if (!Options::useGdbJITInfo())
return;
GdbJIT& logger = singleton();
size_t size = code.size();
auto* executableAddress = code.code().untaggedPtr();
if (!size) {
dataLogLnIf(GdbJITInternal::verbose, "0 size record ", name, " ", RawPointer(executableAddress));
return;
}
Locker locker { logger.m_lock };
auto region = unsafeMakeSpan(executableAddress, size);
removeJITCodeEntries(logger.m_map, region);
auto* entry = createELFObject(CodeDescription::create(name, region));
bool shouldDump = false;
addJITCodeEntry(logger.m_map, region, entry, shouldDump, name);
}
} // namespace JSC
WTF_ALLOW_UNSAFE_BUFFER_USAGE_END
#else
namespace JSC {
WTF_MAKE_TZONE_ALLOCATED_IMPL(GdbJIT);
GdbJIT& GdbJIT::singleton()
{
static LazyNeverDestroyed logger;
static std::once_flag onceKey;
std::call_once(onceKey, [] {
logger.construct();
});
return logger.get();
}
void GdbJIT::log(const CString&, MacroAssemblerCodeRef) { }
} // namespace JSC
#endif // OS(DARWIN) || OS(LINUX)
#endif // ENABLE(ASSEMBLER)