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dart / sdk.git / f860b70c98d03b454eb0ad2fba70e4e2c9641a6f / . / runtime / vm / elf.cc
blob: 55b14e84e68c83050c8dab7e10721b0d28fc27e2 [file] [log] [blame]
// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
#include "vm/elf.h"
#include "platform/elf.h"
#include "vm/cpu.h"
#include "vm/dwarf.h"
#include "vm/hash_map.h"
#include "vm/image_snapshot.h"
#include "vm/stack_frame.h"
#include "vm/thread.h"
#include "vm/zone_text_buffer.h"
namespace dart {
#if defined(DART_PRECOMPILER)
// A wrapper around BaseWriteStream that provides methods useful for
// writing ELF files (e.g., using ELF definitions of data sizes).
class ElfWriteStream : public ValueObject {
public:
explicit ElfWriteStream(BaseWriteStream* stream)
: stream_(ASSERT_NOTNULL(stream)) {}
intptr_t Position() const { return stream_->Position(); }
void Align(const intptr_t alignment) {
ASSERT(Utils::IsPowerOfTwo(alignment));
stream_->Align(alignment);
}
void WriteBytes(const uint8_t* b, intptr_t size) {
stream_->WriteBytes(b, size);
}
void WriteByte(uint8_t value) { stream_->WriteByte(value); }
void WriteHalf(uint16_t value) { stream_->WriteFixed(value); }
void WriteWord(uint32_t value) { stream_->WriteFixed(value); }
void WriteAddr(compiler::target::uword value) { stream_->WriteFixed(value); }
void WriteOff(compiler::target::uword value) { stream_->WriteFixed(value); }
#if defined(TARGET_ARCH_IS_64_BIT)
void WriteXWord(uint64_t value) { stream_->WriteFixed(value); }
#endif
private:
BaseWriteStream* const stream_;
};
static constexpr intptr_t kLinearInitValue = -1;
#define DEFINE_LINEAR_FIELD_METHODS(name) \
intptr_t name() const { \
ASSERT(name##_ != kLinearInitValue); \
return name##_; \
} \
bool name##_is_set() const { return name##_ != kLinearInitValue; } \
void set_##name(intptr_t value) { \
ASSERT(value != kLinearInitValue); \
ASSERT_EQUAL(name##_, kLinearInitValue); \
name##_ = value; \
}
#define DEFINE_LINEAR_FIELD(name) intptr_t name##_ = kLinearInitValue;
class BitsContainer;
class Segment;
static constexpr intptr_t kDefaultAlignment = -1;
// Align note sections and segments to 4 byte boundries.
static constexpr intptr_t kNoteAlignment = 4;
class Section : public ZoneAllocated {
public:
Section(elf::SectionHeaderType t,
bool allocate,
bool executable,
bool writable,
intptr_t align = kDefaultAlignment)
: type(t),
flags(EncodeFlags(allocate, executable, writable)),
alignment(align == kDefaultAlignment ? DefaultAlignment(t) : align),
// Non-segments will never have a memory offset, here represented by 0.
memory_offset_(allocate ? kLinearInitValue : 0) {
// Only sections with type SHT_NULL are allowed to have an alignment of 0.
ASSERT(type == elf::SectionHeaderType::SHT_NULL || alignment > 0);
// Non-zero alignments must be a power of 2.
ASSERT(alignment == 0 || Utils::IsPowerOfTwo(alignment));
}
virtual ~Section() {}
// Linker view.
const elf::SectionHeaderType type;
const intptr_t flags;
const intptr_t alignment;
// These are fields that only are not set for most kinds of sections and so we
// set them to a reasonable default.
intptr_t link = elf::SHN_UNDEF;
intptr_t info = 0;
intptr_t entry_size = 0;
#define FOR_EACH_SECTION_LINEAR_FIELD(M) \
M(name) \
M(index) \
M(file_offset)
FOR_EACH_SECTION_LINEAR_FIELD(DEFINE_LINEAR_FIELD_METHODS);
virtual intptr_t FileSize() const = 0;
// Loader view.
#define FOR_EACH_SEGMENT_LINEAR_FIELD(M) M(memory_offset)
FOR_EACH_SEGMENT_LINEAR_FIELD(DEFINE_LINEAR_FIELD_METHODS);
// Each section belongs to at most one PT_LOAD segment.
Segment* load_segment = nullptr;
virtual intptr_t MemorySize() const = 0;
// Other methods.
bool IsAllocated() const {
return (flags & elf::SHF_ALLOC) == elf::SHF_ALLOC;
}
bool IsExecutable() const {
return (flags & elf::SHF_EXECINSTR) == elf::SHF_EXECINSTR;
}
bool IsWritable() const { return (flags & elf::SHF_WRITE) == elf::SHF_WRITE; }
// Returns whether new content can be added to a section.
bool HasBeenFinalized() const {
if (IsAllocated()) {
// The contents of a section that is allocated (part of a segment) must
// not change after the section is added.
return memory_offset_is_set();
} else {
// Unallocated sections can have new content added until we calculate
// file offsets.
return file_offset_is_set();
}
}
virtual const BitsContainer* AsBitsContainer() const { return nullptr; }
// Writes the file contents of the section.
virtual void Write(ElfWriteStream* stream) = 0;
virtual void WriteSectionHeader(ElfWriteStream* stream) {
#if defined(TARGET_ARCH_IS_32_BIT)
stream->WriteWord(name());
stream->WriteWord(static_cast<uint32_t>(type));
stream->WriteWord(flags);
stream->WriteAddr(memory_offset());
stream->WriteOff(file_offset());
stream->WriteWord(FileSize()); // Has different meaning for BSS.
stream->WriteWord(link);
stream->WriteWord(info);
stream->WriteWord(alignment);
stream->WriteWord(entry_size);
#else
stream->WriteWord(name());
stream->WriteWord(static_cast<uint32_t>(type));
stream->WriteXWord(flags);
stream->WriteAddr(memory_offset());
stream->WriteOff(file_offset());
stream->WriteXWord(FileSize()); // Has different meaning for BSS.
stream->WriteWord(link);
stream->WriteWord(info);
stream->WriteXWord(alignment);
stream->WriteXWord(entry_size);
#endif
}
private:
static intptr_t EncodeFlags(bool allocate, bool executable, bool writable) {
if (!allocate) return 0;
intptr_t flags = elf::SHF_ALLOC;
if (executable) flags |= elf::SHF_EXECINSTR;
if (writable) flags |= elf::SHF_WRITE;
return flags;
}
static intptr_t DefaultAlignment(elf::SectionHeaderType type) {
switch (type) {
case elf::SectionHeaderType::SHT_SYMTAB:
case elf::SectionHeaderType::SHT_DYNSYM:
case elf::SectionHeaderType::SHT_HASH:
case elf::SectionHeaderType::SHT_DYNAMIC:
return compiler::target::kWordSize;
default:
return 1;
}
}
FOR_EACH_SECTION_LINEAR_FIELD(DEFINE_LINEAR_FIELD);
FOR_EACH_SEGMENT_LINEAR_FIELD(DEFINE_LINEAR_FIELD);
#undef FOR_EACH_SECTION_LINEAR_FIELD
#undef FOR_EACH_SEGMENT_LINEAR_FIELD
};
#undef DEFINE_LINEAR_FIELD
#undef DEFINE_LINEAR_FIELD_METHODS
class Segment : public ZoneAllocated {
public:
Segment(Zone* zone,
Section* initial_section,
elf::ProgramHeaderType segment_type)
: type(segment_type),
// Flags for the segment are the same as the initial section.
flags(EncodeFlags(ASSERT_NOTNULL(initial_section)->IsExecutable(),
ASSERT_NOTNULL(initial_section)->IsWritable())),
sections_(zone, 0) {
// Unlike sections, we don't have a reserved segment with the null type,
// so we never should pass this value.
ASSERT(segment_type != elf::ProgramHeaderType::PT_NULL);
// All segments should have at least one section. The first one is added
// during initialization. Unlike others added later, it should already have
// a memory offset since we use it to determine the segment memory offset.
ASSERT(initial_section->IsAllocated());
ASSERT(initial_section->memory_offset_is_set());
// Make sure the memory offset chosen for the initial section is consistent
// with the alignment for the segment.
ASSERT(Utils::IsAligned(initial_section->memory_offset(), Alignment(type)));
sections_.Add(initial_section);
if (type == elf::ProgramHeaderType::PT_LOAD) {
ASSERT(initial_section->load_segment == nullptr);
initial_section->load_segment = this;
}
}
virtual ~Segment() {}
static intptr_t Alignment(elf::ProgramHeaderType segment_type) {
switch (segment_type) {
case elf::ProgramHeaderType::PT_PHDR:
case elf::ProgramHeaderType::PT_DYNAMIC:
return compiler::target::kWordSize;
case elf::ProgramHeaderType::PT_NOTE:
return kNoteAlignment;
default:
return Elf::kPageSize;
}
}
bool IsExecutable() const { return (flags & elf::PF_X) == elf::PF_X; }
bool IsWritable() const { return (flags & elf::PF_W) == elf::PF_W; }
void WriteProgramHeader(ElfWriteStream* stream) {
#if defined(TARGET_ARCH_IS_32_BIT)
stream->WriteWord(static_cast<uint32_t>(type));
stream->WriteOff(FileOffset());
stream->WriteAddr(MemoryOffset()); // Virtual address.
stream->WriteAddr(MemoryOffset()); // Physical address, not used.
stream->WriteWord(FileSize());
stream->WriteWord(MemorySize());
stream->WriteWord(flags);
stream->WriteWord(Alignment(type));
#else
stream->WriteWord(static_cast<uint32_t>(type));
stream->WriteWord(flags);
stream->WriteOff(FileOffset());
stream->WriteAddr(MemoryOffset()); // Virtual address.
stream->WriteAddr(MemoryOffset()); // Physical address, not used.
stream->WriteXWord(FileSize());
stream->WriteXWord(MemorySize());
stream->WriteXWord(Alignment(type));
#endif
}
// Adds the given section to this segment.
//
// Returns whether the Section could be added to the segment. If not, a
// new segment will need to be created for this section.
//
// Sets the memory offset of the section if added.
bool Add(Section* section) {
// We only add additional sections to load segments.
ASSERT(type == elf::ProgramHeaderType::PT_LOAD);
ASSERT(section != nullptr);
// Only sections with the allocate flag set should be added to segments,
// and sections with already-set memory offsets cannot be added.
ASSERT(section->IsAllocated());
ASSERT(!section->memory_offset_is_set());
ASSERT(section->load_segment == nullptr);
switch (sections_.Last()->type) {
// We only use SHT_NULL sections as pseudo sections that will not appear
// in the final ELF file. Don't pack sections into these segments, as we
// may remove/replace the segments during finalization.
case elf::SectionHeaderType::SHT_NULL:
// If the last section in the segments is NOBITS, then we don't add it,
// as otherwise we'll be guaranteed the file offset and memory offset
// won't be page aligned without padding.
case elf::SectionHeaderType::SHT_NOBITS:
return false;
default:
break;
}
// We don't add if the W or X bits don't match.
if (IsExecutable() != section->IsExecutable() ||
IsWritable() != section->IsWritable()) {
return false;
}
auto const start_address = Utils::RoundUp(MemoryEnd(), section->alignment);
section->set_memory_offset(start_address);
sections_.Add(section);
section->load_segment = this;
return true;
}
void Replace(Section* old_section, Section* new_section) {
ASSERT(old_section->load_segment == this);
// All these must be true for replacement to be safe.
ASSERT_EQUAL(static_cast<uint32_t>(old_section->type),
static_cast<uint32_t>(new_section->type));
ASSERT_EQUAL(old_section->MemorySize(), new_section->MemorySize());
ASSERT_EQUAL(old_section->IsExecutable(), new_section->IsExecutable());
ASSERT_EQUAL(old_section->IsWritable(), new_section->IsWritable());
ASSERT(old_section->memory_offset_is_set());
ASSERT(!new_section->memory_offset_is_set());
for (intptr_t i = 0; i < sections_.length(); i++) {
auto const section = sections_[i];
if (section != old_section) {
continue;
}
new_section->set_memory_offset(old_section->memory_offset());
sections_[i] = new_section;
new_section->load_segment = this;
old_section->load_segment = nullptr;
return;
}
UNREACHABLE();
}
intptr_t FileOffset() const { return sections_[0]->file_offset(); }
intptr_t FileSize() const {
auto const last = sections_.Last();
const intptr_t end = last->file_offset() + last->FileSize();
return end - FileOffset();
}
intptr_t MemoryOffset() const { return sections_[0]->memory_offset(); }
intptr_t MemorySize() const {
auto const last = sections_.Last();
const intptr_t end = last->memory_offset() + last->MemorySize();
return end - MemoryOffset();
}
intptr_t MemoryEnd() const { return MemoryOffset() + MemorySize(); }
private:
static constexpr intptr_t kInitValue = -1;
static_assert(kInitValue < 0, "init value must be negative");
static intptr_t EncodeFlags(bool executable, bool writable) {
intptr_t flags = elf::PF_R;
if (executable) flags |= elf::PF_X;
if (writable) flags |= elf::PF_W;
return flags;
}
public:
const elf::ProgramHeaderType type;
const intptr_t flags;
private:
GrowableArray<const Section*> sections_;
};
// Represents the first entry in the section table, which should only contain
// zero values and does not correspond to a memory segment.
class ReservedSection : public Section {
public:
ReservedSection()
: Section(elf::SectionHeaderType::SHT_NULL,
/*allocate=*/false,
/*executable=*/false,
/*writable=*/false,
/*alignment=*/0) {
set_name(0);
set_index(0);
set_file_offset(0);
}
intptr_t FileSize() const { return 0; }
intptr_t MemorySize() const { return 0; }
void Write(ElfWriteStream* stream) {}
};
// Represents portions of the file/memory space which do not correspond to
// actual sections. Should never be added to sections_.
class PseudoSection : public Section {
public:
PseudoSection(bool executable,
bool writable,
intptr_t file_offset,
intptr_t file_size,
intptr_t memory_offset,
intptr_t memory_size)
: Section(elf::SectionHeaderType::SHT_NULL,
/*allocate=*/true,
executable,
writable,
/*alignment=*/0),
file_size_(file_size),
memory_size_(memory_size) {
set_file_offset(file_offset);
set_memory_offset(memory_offset);
}
intptr_t FileSize() const { return file_size_; }
intptr_t MemorySize() const { return memory_size_; }
void WriteSectionHeader(ElfWriteStream* stream) { UNREACHABLE(); }
void Write(ElfWriteStream* stream) { UNREACHABLE(); }
private:
const intptr_t file_size_;
const intptr_t memory_size_;
};
// A segment for representing the program header table self-reference in the
// program header table.
class ProgramTableSelfSegment : public Segment {
public:
ProgramTableSelfSegment(Zone* zone, intptr_t offset, intptr_t size)
: Segment(zone,
new (zone) PseudoSection(/*executable=*/false,
/*writable=*/false,
offset,
size,
offset,
size),
elf::ProgramHeaderType::PT_PHDR) {}
};
// A segment for representing the program header table load segment in the
// program header table.
class ProgramTableLoadSegment : public Segment {
public:
// The Android dynamic linker in Jelly Bean incorrectly assumes that all
// non-writable segments are continguous. Since the BSS segment comes directly
// after the program header segment, we must make this segment writable so
// later non-writable segments does not cause the BSS to be also marked as
// read-only.
//
// The bug is here:
// https://github.com/aosp-mirror/platform_bionic/blob/94963af28e445384e19775a838a29e6a71708179/linker/linker.c#L1991-L2001
explicit ProgramTableLoadSegment(Zone* zone, intptr_t size)
: Segment(zone,
// This segment should always start at address 0.
new (zone) PseudoSection(/*executable=*/false,
/*writable=*/true,
0,
size,
0,
size),
elf::ProgramHeaderType::PT_LOAD) {}
};
class BitsContainer : public Section {
public:
// Fully specified BitsContainer information.
BitsContainer(elf::SectionHeaderType type,
bool allocate,
bool executable,
bool writable,
intptr_t size,
const uint8_t* bytes,
int alignment = kDefaultAlignment)
: Section(type, allocate, executable, writable, alignment),
file_size_(type == elf::SectionHeaderType::SHT_NOBITS ? 0 : size),
memory_size_(allocate ? size : 0),
bytes_(bytes) {
ASSERT(type == elf::SectionHeaderType::SHT_NOBITS || bytes != nullptr);
}
// For BitsContainers used only as sections.
BitsContainer(elf::SectionHeaderType type,
intptr_t size,
const uint8_t* bytes,
intptr_t alignment = kDefaultAlignment)
: BitsContainer(type,
/*allocate=*/false,
/*executable=*/false,
/*writable=*/false,
size,
bytes,
alignment) {}
// For BitsContainers used as segments whose type differ on the type of the
// ELF file. Creates an elf::SHT_PROGBITS section if type is Snapshot,
// otherwise creates an elf::SHT_NOBITS section.
BitsContainer(Elf::Type t,
bool executable,
bool writable,
intptr_t size,
const uint8_t* bytes,
intptr_t alignment = kDefaultAlignment)
: BitsContainer(t == Elf::Type::Snapshot
? elf::SectionHeaderType::SHT_PROGBITS
: elf::SectionHeaderType::SHT_NOBITS,
/*allocate=*/true,
executable,
writable,
size,
bytes,
alignment) {}
const BitsContainer* AsBitsContainer() const { return this; }
void Write(ElfWriteStream* stream) {
if (type != elf::SectionHeaderType::SHT_NOBITS) {
stream->WriteBytes(bytes_, FileSize());
}
}
intptr_t FileSize() const { return file_size_; }
intptr_t MemorySize() const { return memory_size_; }
const uint8_t* bytes() const { return bytes_; }
private:
const intptr_t file_size_;
const intptr_t memory_size_;
const uint8_t* const bytes_;
};
class StringTable : public Section {
public:
explicit StringTable(Zone* zone, bool allocate)
: Section(elf::SectionHeaderType::SHT_STRTAB,
allocate,
/*executable=*/false,
/*writable=*/false),
dynamic_(allocate),
text_(zone, 128),
text_indices_(zone) {
AddString("");
}
intptr_t FileSize() const { return text_.length(); }
intptr_t MemorySize() const { return dynamic_ ? FileSize() : 0; }
void Write(ElfWriteStream* stream) {
stream->WriteBytes(reinterpret_cast<const uint8_t*>(text_.buffer()),
text_.length());
}
intptr_t AddString(const char* str) {
ASSERT(str != nullptr);
if (auto const kv = text_indices_.Lookup(str)) {
return kv->value;
}
intptr_t offset = text_.length();
text_.AddString(str);
text_.AddChar('\0');
text_indices_.Insert({str, offset});
return offset;
}
const char* At(intptr_t index) {
ASSERT(index < text_.length());
return text_.buffer() + index;
}
static const intptr_t kNotIndexed = CStringIntMapKeyValueTrait::kNoValue;
// Returns the index of |str| if it is present in the string table
// and |kNotIndexed| otherwise.
intptr_t Lookup(const char* str) const {
return text_indices_.LookupValue(str);
}
const bool dynamic_;
ZoneTextBuffer text_;
CStringIntMap text_indices_;
};
class Symbol : public ZoneAllocated {
public:
Symbol(const char* cstr,
intptr_t name,
intptr_t binding,
intptr_t type,
intptr_t section,
intptr_t offset,
intptr_t size)
: name_index(name),
binding(binding),
type(type),
section_index(section),
offset(offset),
size(size),
cstr_(cstr) {}
void Write(ElfWriteStream* stream) const {
const intptr_t start = stream->Position();
stream->WriteWord(name_index);
#if defined(TARGET_ARCH_IS_32_BIT)
stream->WriteAddr(offset);
stream->WriteWord(size);
stream->WriteByte(elf::SymbolInfo(binding, type));
stream->WriteByte(0);
stream->WriteHalf(section_index);
#else
stream->WriteByte(elf::SymbolInfo(binding, type));
stream->WriteByte(0);
stream->WriteHalf(section_index);
stream->WriteAddr(offset);
stream->WriteXWord(size);
#endif
ASSERT_EQUAL(stream->Position() - start, sizeof(elf::Symbol));
}
const intptr_t name_index;
const intptr_t binding;
const intptr_t type;
const intptr_t section_index;
const intptr_t offset;
const intptr_t size;
private:
friend class SymbolHashTable; // For cstr_ access.
const char* const cstr_;
};
class SymbolTable : public Section {
public:
SymbolTable(Zone* zone, StringTable* table, bool dynamic)
: Section(dynamic ? elf::SectionHeaderType::SHT_DYNSYM
: elf::SectionHeaderType::SHT_SYMTAB,
dynamic,
/*executable=*/false,
/*writable=*/false),
zone_(zone),
table_(table),
dynamic_(dynamic),
symbols_(zone, 1),
by_name_index_(zone) {
entry_size = sizeof(elf::Symbol);
// The first symbol table entry is reserved and must be all zeros.
// (String tables always have the empty string at the 0th index.)
AddSymbol("", elf::STB_LOCAL, elf::STT_NOTYPE, elf::SHN_UNDEF, /*offset=*/0,
/*size=*/0);
}
intptr_t FileSize() const { return Length() * entry_size; }
intptr_t MemorySize() const { return dynamic_ ? FileSize() : 0; }
void Write(ElfWriteStream* stream) {
for (intptr_t i = 0; i < Length(); i++) {
auto const symbol = At(i);
const intptr_t start = stream->Position();
symbol->Write(stream);
ASSERT_EQUAL(stream->Position() - start, entry_size);
}
}
void AddSymbol(const char* name,
intptr_t binding,
intptr_t type,
intptr_t section_index,
intptr_t offset,
intptr_t size) {
ASSERT(!table_->HasBeenFinalized());
auto const name_index = table_->AddString(name);
ASSERT(by_name_index_.Lookup(name_index) == nullptr);
auto const symbol = new (zone_)
Symbol(name, name_index, binding, type, section_index, offset, size);
symbols_.Add(symbol);
by_name_index_.Insert(name_index, symbol);
// The info field on a symbol table section holds the index of the first
// non-local symbol, so they can be skipped if desired. Thus, we need to
// make sure local symbols are before any non-local ones.
if (binding == elf::STB_LOCAL) {
if (info != symbols_.length() - 1) {
// There are non-local symbols, as otherwise [info] would be the
// index of the new symbol. Since the order doesn't otherwise matter,
// swap the new local symbol with the value at index [info], so when
// [info] is incremented it will point just past the new local symbol.
ASSERT(symbols_[info]->binding != elf::STB_LOCAL);
symbols_.Swap(info, symbols_.length() - 1);
}
info += 1;
}
}
intptr_t Length() const { return symbols_.length(); }
const Symbol* At(intptr_t i) const { return symbols_[i]; }
const Symbol* Find(const char* name) const {
ASSERT(name != nullptr);
auto const name_index = table_->Lookup(name);
return by_name_index_.Lookup(name_index);
}
private:
Zone* const zone_;
StringTable* const table_;
const bool dynamic_;
GrowableArray<const Symbol*> symbols_;
mutable IntMap<const Symbol*> by_name_index_;
};
static uint32_t ElfHash(const unsigned char* name) {
uint32_t h = 0;
while (*name != '\0') {
h = (h << 4) + *name++;
uint32_t g = h & 0xf0000000;
h ^= g;
h ^= g >> 24;
}
return h;
}
class SymbolHashTable : public Section {
public:
SymbolHashTable(Zone* zone, StringTable* strtab, SymbolTable* symtab)
: Section(elf::SectionHeaderType::SHT_HASH,
/*allocate=*/true,
/*executable=*/false,
/*writable=*/false) {
link = symtab->index();
entry_size = sizeof(int32_t);
nchain_ = symtab->Length();
nbucket_ = symtab->Length();
bucket_ = zone->Alloc<int32_t>(nbucket_);
for (intptr_t i = 0; i < nbucket_; i++) {
bucket_[i] = elf::STN_UNDEF;
}
chain_ = zone->Alloc<int32_t>(nchain_);
for (intptr_t i = 0; i < nchain_; i++) {
chain_[i] = elf::STN_UNDEF;
}
for (intptr_t i = 1; i < symtab->Length(); i++) {
auto const symbol = symtab->At(i);
uint32_t hash = ElfHash((const unsigned char*)symbol->cstr_);
uint32_t probe = hash % nbucket_;
chain_[i] = bucket_[probe]; // next = head
bucket_[probe] = i; // head = symbol
}
}
intptr_t FileSize() const { return entry_size * (nbucket_ + nchain_ + 2); }
intptr_t MemorySize() const { return FileSize(); }
void Write(ElfWriteStream* stream) {
stream->WriteWord(nbucket_);
stream->WriteWord(nchain_);
for (intptr_t i = 0; i < nbucket_; i++) {
stream->WriteWord(bucket_[i]);
}
for (intptr_t i = 0; i < nchain_; i++) {
stream->WriteWord(chain_[i]);
}
}
private:
int32_t nbucket_;
int32_t nchain_;
int32_t* bucket_; // "Head"
int32_t* chain_; // "Next"
};
class DynamicTable : public Section {
public:
DynamicTable(Zone* zone,
StringTable* strtab,
SymbolTable* symtab,
SymbolHashTable* hash)
: Section(elf::SectionHeaderType::SHT_DYNAMIC,
/*allocate=*/true,
/*executable=*/false,
/*writable=*/true) {
link = strtab->index();
entry_size = sizeof(elf::DynamicEntry);
AddEntry(zone, elf::DynamicEntryType::DT_HASH, hash->memory_offset());
AddEntry(zone, elf::DynamicEntryType::DT_STRTAB, strtab->memory_offset());
AddEntry(zone, elf::DynamicEntryType::DT_STRSZ, strtab->MemorySize());
AddEntry(zone, elf::DynamicEntryType::DT_SYMTAB, symtab->memory_offset());
AddEntry(zone, elf::DynamicEntryType::DT_SYMENT, sizeof(elf::Symbol));
AddEntry(zone, elf::DynamicEntryType::DT_NULL, 0);
}
intptr_t FileSize() const { return entries_.length() * entry_size; }
intptr_t MemorySize() const { return FileSize(); }
void Write(ElfWriteStream* stream) {
for (intptr_t i = 0; i < entries_.length(); i++) {
entries_[i]->Write(stream);
}
}
struct Entry : public ZoneAllocated {
Entry(elf::DynamicEntryType tag, intptr_t value) : tag(tag), value(value) {}
void Write(ElfWriteStream* stream) {
const intptr_t start = stream->Position();
#if defined(TARGET_ARCH_IS_32_BIT)
stream->WriteWord(static_cast<uint32_t>(tag));
stream->WriteAddr(value);
#else
stream->WriteXWord(static_cast<uint64_t>(tag));
stream->WriteAddr(value);
#endif
ASSERT_EQUAL(stream->Position() - start, sizeof(elf::DynamicEntry));
}
elf::DynamicEntryType tag;
intptr_t value;
};
void AddEntry(Zone* zone, elf::DynamicEntryType tag, intptr_t value) {
auto const entry = new (zone) Entry(tag, value);
entries_.Add(entry);
}
private:
GrowableArray<Entry*> entries_;
};
// A segment for representing the dynamic table segment in the program header
// table. There is no corresponding section for this segment.
class DynamicSegment : public Segment {
public:
explicit DynamicSegment(Zone* zone, DynamicTable* dynamic)
: Segment(zone, dynamic, elf::ProgramHeaderType::PT_DYNAMIC) {}
};
// A segment for representing the dynamic table segment in the program header
// table. There is no corresponding section for this segment.
class NoteSegment : public Segment {
public:
NoteSegment(Zone* zone, Section* note)
: Segment(zone, note, elf::ProgramHeaderType::PT_NOTE) {
ASSERT_EQUAL(static_cast<uint32_t>(note->type),
static_cast<uint32_t>(elf::SectionHeaderType::SHT_NOTE));
}
};
// We assume that the final program table fits in a single page of memory.
static constexpr intptr_t kProgramTableSegmentSize = Elf::kPageSize;
// Here, both VM and isolate will be compiled into a single snapshot.
// In assembly generation, each serialized text section gets a separate
// pointer into the BSS segment and BSS slots are created for each, since
// we may not serialize both VM and isolate. Here, we always serialize both,
// so make a BSS segment large enough for both, with the VM entries coming
// first.
static constexpr intptr_t kBssVmSize =
BSS::kVmEntryCount * compiler::target::kWordSize;
static constexpr intptr_t kBssIsolateSize =
BSS::kIsolateEntryCount * compiler::target::kWordSize;
static constexpr intptr_t kBssSize = kBssVmSize + kBssIsolateSize;
// For the build ID, we generate a 128-bit hash, where each 32 bits is a hash of
// the contents of the following segments in order:
//
// .text(VM) | .text(Isolate) | .rodata(VM) | .rodata(Isolate)
static constexpr const char* kBuildIdSegmentNames[]{
kVmSnapshotInstructionsAsmSymbol,
kIsolateSnapshotInstructionsAsmSymbol,
kVmSnapshotDataAsmSymbol,
kIsolateSnapshotDataAsmSymbol,
};
static constexpr intptr_t kBuildIdSegmentNamesLength =
ARRAY_SIZE(kBuildIdSegmentNames);
// Includes the note name, but not the description.
static constexpr intptr_t kBuildIdHeaderSize =
sizeof(elf::Note) + sizeof(elf::ELF_NOTE_GNU);
Elf::Elf(Zone* zone, BaseWriteStream* stream, Type type, Dwarf* dwarf)
: zone_(zone),
unwrapped_stream_(stream),
type_(type),
dwarf_(dwarf),
bss_(CreateBSS(zone, type, kBssSize)),
shstrtab_(new (zone) StringTable(zone, /*allocate=*/false)),
dynstrtab_(new (zone) StringTable(zone, /*allocate=*/true)),
dynsym_(new (zone) SymbolTable(zone, dynstrtab_, /*dynamic=*/true)) {
// Separate debugging information should always have a Dwarf object.
ASSERT(type_ == Type::Snapshot || dwarf_ != nullptr);
// Assumed by various offset logic in this file.
ASSERT_EQUAL(unwrapped_stream_->Position(), 0);
// The first section in the section header table is always a reserved
// entry containing only 0 values.
sections_.Add(new (zone_) ReservedSection());
if (!IsStripped()) {
// Not a stripped ELF file, so allocate static string and symbol tables.
strtab_ = new (zone_) StringTable(zone_, /* allocate= */ false);
symtab_ = new (zone_) SymbolTable(zone, strtab_, /*dynamic=*/false);
}
// We add an initial segment to represent reserved space for the program
// header, and so we can always assume there's at least one segment in the
// segments_ array. We later remove this and replace it with appropriately
// calculated segments in Elf::FinalizeProgramTable().
auto const start_segment =
new (zone_) ProgramTableLoadSegment(zone_, kProgramTableSegmentSize);
segments_.Add(start_segment);
// We allocate an initial build ID of all zeroes, since we need the build ID
// memory offset for the InstructionsSection (see BlobImageWriter::WriteText).
// We replace it with the real build ID during finalization. (We add this
// prior to BSS because we make the BuildID section writable also, so they are
// placed in the same segment before any non-writable ones, and if we add it
// after, then in separate debugging information, it'll go into a separate
// segment because the BSS section for debugging info is NOBITS.)
{
uint32_t zeroes[kBuildIdSegmentNamesLength] = {0};
build_id_ = CreateBuildIdNote(&zeroes, sizeof(zeroes));
AddSection(build_id_, kBuildIdNoteName, kSnapshotBuildIdAsmSymbol);
}
// Note that the BSS segment must be in the first user-defined segment because
// it cannot be placed in between any two non-writable segments, due to a bug
// in Jelly Bean's ELF loader. (For this reason, the program table segments
// generated during finalization are marked as writable.) See also
// Elf::WriteProgramTable().
//
// We add it in all cases, even to the separate debugging information ELF,
// to ensure that relocated addresses are consistent between ELF snapshots
// and ELF separate debugging information.
auto const bss_start = AddSection(bss_, ".bss");
// For the BSS section, we add two local symbols to the static symbol table,
// one for each isolate. We use local symbols because these addresses are only
// used for relocation. (This matches the behavior in the assembly output,
// where these symbols are also local.)
AddStaticSymbol(kVmSnapshotBssAsmSymbol, elf::STB_LOCAL, elf::STT_SECTION,
bss_->index(), bss_start, kBssVmSize);
AddStaticSymbol(kIsolateSnapshotBssAsmSymbol, elf::STB_LOCAL,
elf::STT_SECTION, bss_->index(), bss_start + kBssVmSize,
kBssIsolateSize);
}
intptr_t Elf::NextMemoryOffset(intptr_t alignment) const {
// Without more information, we won't know whether we might create a new
// segment or put the section into the current one. Thus, for now, only allow
// the offset to be queried ahead of time if it matches the load segment
// alignment.
auto const type = elf::ProgramHeaderType::PT_LOAD;
ASSERT_EQUAL(alignment, Segment::Alignment(type));
return Utils::RoundUp(LastLoadSegment()->MemoryEnd(), alignment);
}
uword Elf::SymbolAddress(const char* name) const {
ASSERT(name != nullptr);
// Check the static symbol table first if it exists, since the dynamic
// table is a subset of it. Fall back on the dynamic otherwise.
if (symtab_ != nullptr) {
if (auto const symbol = symtab_->Find(name)) {
return symbol->offset;
}
} else if (auto const symbol = dynsym_->Find(name)) {
return symbol->offset;
}
// If stripping, then we won't have symbols for the BSS sections because
// they're only added to the static symbol table. Check for these special
// cases before returning kNoSectionStart.
if (strcmp(name, kVmSnapshotBssAsmSymbol) == 0) {
ASSERT(bss_ != nullptr);
ASSERT(bss_->memory_offset_is_set());
return bss_->memory_offset();
} else if (strcmp(name, kIsolateSnapshotBssAsmSymbol) == 0) {
ASSERT(bss_ != nullptr);
ASSERT(bss_->memory_offset_is_set());
return bss_->memory_offset() + kBssVmSize;
}
return kNoSectionStart;
}
intptr_t Elf::AddSection(Section* section,
const char* name,
const char* symbol_name) {
ASSERT(section_table_file_size_ < 0);
ASSERT(!shstrtab_->HasBeenFinalized());
section->set_name(shstrtab_->AddString(name));
section->set_index(sections_.length());
sections_.Add(section);
// No memory offset, so just return -1.
if (!section->IsAllocated()) return -1;
ASSERT(program_table_file_size_ < 0);
auto const last_load = LastLoadSegment();
if (!last_load->Add(section)) {
// We can't add this section to the last load segment, so create a new one.
// The new segment starts at the next aligned address.
auto const type = elf::ProgramHeaderType::PT_LOAD;
intptr_t alignment =
Utils::Maximum(section->alignment, Segment::Alignment(type));
auto const start_address =
Utils::RoundUp(last_load->MemoryEnd(), alignment);
section->set_memory_offset(start_address);
auto const segment = new (zone_) Segment(zone_, section, type);
segments_.Add(segment);
}
if (symbol_name != nullptr) {
// While elf::STT_SECTION might seem more appropriate, section symbols are
// usually local and dlsym won't return them.
AddDynamicSymbol(symbol_name, elf::STB_GLOBAL, elf::STT_FUNC,
section->index(), section->memory_offset(),
section->MemorySize());
}
return section->memory_offset();
}
void Elf::ReplaceSection(Section* old_section, Section* new_section) {
ASSERT(section_table_file_size_ < 0);
ASSERT(old_section->index_is_set());
ASSERT(!new_section->index_is_set());
ASSERT_EQUAL(new_section->IsAllocated(), old_section->IsAllocated());
new_section->set_name(old_section->name());
new_section->set_index(old_section->index());
sections_[old_section->index()] = new_section;
if (!old_section->IsAllocated()) {
return;
}
ASSERT(program_table_file_size_ < 0);
ASSERT(old_section->load_segment != nullptr);
old_section->load_segment->Replace(old_section, new_section);
}
intptr_t Elf::AddText(const char* name, const uint8_t* bytes, intptr_t size) {
auto const image = new (zone_) BitsContainer(type_, /*executable=*/true,
/*writable=*/false, size, bytes,
ImageWriter::kTextAlignment);
return AddSection(image, ".text", name);
}
Section* Elf::CreateBSS(Zone* zone, Type type, intptr_t size) {
uint8_t* bytes = nullptr;
if (type == Type::Snapshot) {
// Ideally the BSS segment would take no space in the object, but Android's
// "strip" utility truncates the memory-size of our segments to their
// file-size.
//
// Therefore we must insert zero-filled pages for the BSS.
bytes = zone->Alloc<uint8_t>(size);
memset(bytes, 0, size);
}
return new (zone) BitsContainer(type, /*executable=*/false, /*writable=*/true,
kBssSize, bytes, ImageWriter::kBssAlignment);
}
intptr_t Elf::AddROData(const char* name, const uint8_t* bytes, intptr_t size) {
auto const image = new (zone_) BitsContainer(type_, /*executable=*/false,
/*writable=*/false, size, bytes,
ImageWriter::kRODataAlignment);
return AddSection(image, ".rodata", name);
}
void Elf::AddDebug(const char* name, const uint8_t* bytes, intptr_t size) {
ASSERT(!IsStripped());
ASSERT(bytes != nullptr);
auto const image = new (zone_)
BitsContainer(elf::SectionHeaderType::SHT_PROGBITS, size, bytes);
AddSection(image, name);
}
void Elf::AddLocalSymbol(const char* name,
intptr_t type,
intptr_t offset,
intptr_t size) {
const intptr_t section_index = sections_.length();
// Assume the next section will go into its own segment (currently true
// because we write writable sections, data vm (non-writable, non-executable),
// text vm (executable), data isolate (non-executable), text isolate
// (executable), and we only call this for data and text sections).
const intptr_t address =
NextMemoryOffset(ImageWriter::kTextAlignment) + offset;
AddStaticSymbol(name, elf::STB_LOCAL, type, section_index, address, size);
}
void Elf::AddDynamicSymbol(const char* name,
intptr_t binding,
intptr_t type,
intptr_t section_index,
intptr_t address,
intptr_t size) {
ASSERT(!dynsym_->HasBeenFinalized());
dynsym_->AddSymbol(name, binding, type, section_index, address, size);
// Some tools assume the static symbol table is a superset of the dynamic
// symbol table when it exists (see dartbug.com/41783).
AddStaticSymbol(name, binding, type, section_index, address, size);
}
void Elf::AddStaticSymbol(const char* name,
intptr_t binding,
intptr_t type,
intptr_t section_index,
intptr_t address,
intptr_t size) {
if (IsStripped()) return; // No static info kept in stripped ELF files.
ASSERT(!symtab_->HasBeenFinalized());
symtab_->AddSymbol(name, binding, type, section_index, address, size);
}
#if defined(DART_PRECOMPILER)
class DwarfElfStream : public DwarfWriteStream {
public:
explicit DwarfElfStream(Zone* zone,
NonStreamingWriteStream* stream,
const SymbolTable* table)
: zone_(ASSERT_NOTNULL(zone)),
stream_(ASSERT_NOTNULL(stream)),
table_(table) {}
void sleb128(intptr_t value) { stream_->WriteSLEB128(value); }
void uleb128(uintptr_t value) { stream_->WriteLEB128(value); }
void u1(uint8_t value) { stream_->WriteByte(value); }
void u2(uint16_t value) { stream_->WriteFixed(value); }
void u4(uint32_t value) { stream_->WriteFixed(value); }
void u8(uint64_t value) { stream_->WriteFixed(value); }
void string(const char* cstr) { // NOLINT
// Unlike stream_->WriteString(), we want the null terminator written.
stream_->WriteBytes(cstr, strlen(cstr) + 1);
}
intptr_t ReserveSize(const char* prefix, intptr_t* start) {
ASSERT(start != nullptr);
intptr_t fixup = stream_->Position();
// We assume DWARF v2, so all sizes are 32-bit.
u4(0);
// All sizes for DWARF sections measure the size of the section data _after_
// the size value.
*start = stream_->Position();
return fixup;
}
void SetSize(intptr_t fixup, const char* prefix, intptr_t start) {
const intptr_t old_position = stream_->Position();
stream_->SetPosition(fixup);
stream_->WriteFixed(static_cast<uint32_t>(old_position - start));
stream_->SetPosition(old_position);
}
void OffsetFromSymbol(const char* symbol, intptr_t offset) {
addr(RelocatedAddress(symbol, offset));
}
void DistanceBetweenSymbolOffsets(const char* symbol1,
intptr_t offset1,
const char* symbol2,
intptr_t offset2) {
auto const address1 = RelocatedAddress(symbol1, offset1);
auto const address2 = RelocatedAddress(symbol2, offset2);
RELEASE_ASSERT(address1 >= address2);
auto const delta = address1 - address2;
uleb128(delta);
}
void InitializeAbstractOrigins(intptr_t size) {
abstract_origins_size_ = size;
abstract_origins_ = zone_->Alloc<uint32_t>(abstract_origins_size_);
}
void RegisterAbstractOrigin(intptr_t index) {
ASSERT(abstract_origins_ != nullptr);
ASSERT(index < abstract_origins_size_);
abstract_origins_[index] = stream_->Position();
}
void AbstractOrigin(intptr_t index) { u4(abstract_origins_[index]); }
private:
uword RelocatedAddress(const char* name, intptr_t offset) {
auto const symbol = table_->Find(name);
ASSERT(symbol != nullptr);
return symbol->offset + offset;
}
void addr(uword value) {
#if defined(TARGET_ARCH_IS_32_BIT)
u4(value);
#else
u8(value);
#endif
}
Zone* const zone_;
NonStreamingWriteStream* const stream_;
const SymbolTable* table_;
uint32_t* abstract_origins_ = nullptr;
intptr_t abstract_origins_size_ = -1;
DISALLOW_COPY_AND_ASSIGN(DwarfElfStream);
};
static constexpr intptr_t kInitialDwarfBufferSize = 64 * KB;
#endif
Segment* Elf::LastLoadSegment() const {
for (intptr_t i = segments_.length() - 1; i >= 0; i--) {
auto const segment = segments_.At(i);
if (segment->type == elf::ProgramHeaderType::PT_LOAD) {
return segment;
}
}
// There should always be a load segment, since one is added in construction.
UNREACHABLE();
}
const Section* Elf::FindSectionForAddress(intptr_t address) const {
for (auto const section : sections_) {
if (!section->IsAllocated()) continue;
auto const start = section->memory_offset();
auto const end = start + section->MemorySize();
if (address >= start && address < end) {
return section;
}
}
return nullptr;
}
void Elf::FinalizeEhFrame() {
#if defined(DART_PRECOMPILER) && \
(defined(TARGET_ARCH_ARM) || defined(TARGET_ARCH_ARM64))
// Multiplier which will be used to scale operands of DW_CFA_offset and
// DW_CFA_val_offset.
const intptr_t kDataAlignment = compiler::target::kWordSize;
const uint8_t DW_CFA_offset = 0x80;
const uint8_t DW_CFA_val_offset = 0x14;
const uint8_t DW_CFA_def_cfa = 0x0c;
// Relocation from .eh_frame into bytes within some previously emitted
// section.
struct Reloc {
intptr_t target_memory_offset;
intptr_t source_offset;
};
GrowableArray<Reloc> relocs(2);
ZoneWriteStream stream(zone(), kInitialDwarfBufferSize);
DwarfElfStream dwarf_stream(zone_, &stream, /*symtab=*/nullptr);
// Emits length prefixed CIE or FDE, returns starting offset.
auto emit_record = [&](auto&& body) -> intptr_t {
const intptr_t start = stream.Position();
stream.WriteFixed<uint32_t>(0);
body();
stream.Align(compiler::target::kWordSize);
const intptr_t end = stream.Position();
stream.SetPosition(start);
// Write length not counting the length field itself.
stream.WriteFixed(static_cast<uint32_t>(end - start - 4));
stream.SetPosition(end);
return start;
};
// Emit pcrel|sdata4 reference to the target memory offset.
auto add_pcrel_ref = [&](intptr_t target_memory_offset) {
relocs.Add({target_memory_offset, stream.Position()});
dwarf_stream.u4(0);
};
// Emit CIE.
const intptr_t cie_position = emit_record([&]() {
dwarf_stream.u4(0); // CIE
dwarf_stream.u1(1); // Version (must be 1 or 3)
// Augmentation String
dwarf_stream.string("zR"); // NOLINT
dwarf_stream.uleb128(1); // Code alignment (must be 1).
dwarf_stream.sleb128(kDataAlignment); // Data alignment
dwarf_stream.u1(
ConcreteRegister(LINK_REGISTER)); // Return address register
dwarf_stream.uleb128(1); // Augmentation size
dwarf_stream.u1(0x1b); // FDE encoding: DW_EH_PE_pcrel | DW_EH_PE_sdata4
// CFA is FP+0
dwarf_stream.u1(DW_CFA_def_cfa);
dwarf_stream.uleb128(FP);
dwarf_stream.uleb128(0);
});
// Emit an FDE covering each .text section.
const auto text_name = shstrtab_->Lookup(".text");
ASSERT(text_name != StringTable::kNotIndexed);
for (auto section : sections_) {
if (section->name() == text_name) {
RELEASE_ASSERT(section->memory_offset_is_set());
emit_record([&]() {
// Offset to CIE. Note that unlike pcrel this offset is encoded
// backwards: it will be subtracted from the current position.
dwarf_stream.u4(stream.Position() - cie_position);
add_pcrel_ref(section->memory_offset()); // Start address.
dwarf_stream.u4(section->MemorySize()); // Size.
dwarf_stream.u1(0); // Augmentation Data length.
// FP at FP+kSavedCallerPcSlotFromFp*kWordSize
COMPILE_ASSERT(kSavedCallerFpSlotFromFp >= 0);
dwarf_stream.u1(DW_CFA_offset | FP);
dwarf_stream.uleb128(kSavedCallerFpSlotFromFp);
// LR at FP+kSavedCallerPcSlotFromFp*kWordSize
COMPILE_ASSERT(kSavedCallerPcSlotFromFp >= 0);
dwarf_stream.u1(DW_CFA_offset | ConcreteRegister(LINK_REGISTER));
dwarf_stream.uleb128(kSavedCallerPcSlotFromFp);
// SP is FP+kCallerSpSlotFromFp*kWordSize
COMPILE_ASSERT(kCallerSpSlotFromFp >= 0);
dwarf_stream.u1(DW_CFA_val_offset);
#if defined(TARGET_ARCH_ARM64)
dwarf_stream.uleb128(ConcreteRegister(CSP));
#elif defined(TARGET_ARCH_ARM)
dwarf_stream.uleb128(SP);
#else
#error "Unsupported .eh_frame architecture"
#endif
dwarf_stream.uleb128(kCallerSpSlotFromFp);
});
}
}
dwarf_stream.u4(0); // end of section
// Add section and then relocate its contents.
auto const eh_frame = new (zone_) BitsContainer(
type_, false, false, stream.bytes_written(), stream.buffer());
AddSection(eh_frame, ".eh_frame");
// Relocate contents now that we have memory_offset assigned.
for (auto& reloc : relocs) {
const intptr_t pcrel_offset =
reloc.target_memory_offset -
(eh_frame->memory_offset() + reloc.source_offset);
// Note: IsInt<int32_t>(32, ...) does not work correctly.
RELEASE_ASSERT(kBitsPerWord == 32 || Utils::IsInt(32, pcrel_offset));
*reinterpret_cast<int32_t*>(stream.buffer() + reloc.source_offset) =
static_cast<int32_t>(pcrel_offset);
}
#endif // defined(DART_PRECOMPILER) && \
// (defined(TARGET_ARCH_ARM) || defined(TARGET_ARCH_ARM64))
}
void Elf::FinalizeDwarfSections() {
if (dwarf_ == nullptr) return;
#if defined(DART_PRECOMPILER)
{
ZoneWriteStream stream(zone(), kInitialDwarfBufferSize);
// We can use symtab_ without checking because this is an unstripped
// snapshot or separate debugging information, both of which have static
// symbol tables, and the static symbol table is a superset of the dynamic.
DwarfElfStream dwarf_stream(zone_, &stream, symtab_);
dwarf_->WriteAbbreviations(&dwarf_stream);
AddDebug(".debug_abbrev", stream.buffer(), stream.bytes_written());
}
{
ZoneWriteStream stream(zone(), kInitialDwarfBufferSize);
DwarfElfStream dwarf_stream(zone_, &stream, symtab_);
dwarf_->WriteDebugInfo(&dwarf_stream);
AddDebug(".debug_info", stream.buffer(), stream.bytes_written());
}
{
ZoneWriteStream stream(zone(), kInitialDwarfBufferSize);
DwarfElfStream dwarf_stream(zone_, &stream, symtab_);
dwarf_->WriteLineNumberProgram(&dwarf_stream);
AddDebug(".debug_line", stream.buffer(), stream.bytes_written());
}
#endif
}
void Elf::Finalize() {
if (auto const new_build_id = GenerateFinalBuildId()) {
ReplaceSection(build_id_, new_build_id);
// Add a PT_NOTE segment for the build ID.
segments_.Add(new (zone_) NoteSegment(zone_, new_build_id));
}
// Adding the dynamic symbol table and associated sections.
AddSection(dynstrtab_, ".dynstr");
AddSection(dynsym_, ".dynsym");
dynsym_->link = dynstrtab_->index();
auto const hash = new (zone_) SymbolHashTable(zone_, dynstrtab_, dynsym_);
AddSection(hash, ".hash");
// Must come before .dynamic, because .dynamic is writable and
// .eh_frame is not. See restriction in Elf::WriteProgramTable.
FinalizeEhFrame();
auto const dynamic =
new (zone_) DynamicTable(zone_, dynstrtab_, dynsym_, hash);
AddSection(dynamic, ".dynamic");
// Add a PT_DYNAMIC segment for the dynamic symbol table.
segments_.Add(new (zone_) DynamicSegment(zone_, dynamic));
// Currently, we add all (non-reserved) unallocated sections after all
// allocated sections. If we put unallocated sections between allocated
// sections, they would affect the file offset but not the memory offset
// of the later allocated sections.
//
// However, memory offsets must be page-aligned to the file offset for the
// ELF file to be successfully loaded. This means we'd either have to add
// extra padding _or_ determine file offsets before memory offsets. The
// latter would require us to handle BSS relocations during ELF finalization,
// instead of while writing the .text section content.
if (!IsStripped()) {
AddSection(strtab_, ".strtab");
AddSection(symtab_, ".symtab");
symtab_->link = strtab_->index();
}
AddSection(shstrtab_, ".shstrtab");
FinalizeDwarfSections();
// At this point, all non-programmatically calculated sections and segments
// have been added. Add any programatically calculated sections and segments
// and then calculate file offsets.
FinalizeProgramTable();
ComputeFileOffsets();
// Finally, write the ELF file contents.
ElfWriteStream wrapped(unwrapped_stream_);
WriteHeader(&wrapped);
WriteProgramTable(&wrapped);
WriteSections(&wrapped);
WriteSectionTable(&wrapped);
}
static uint32_t HashBitsContainer(const BitsContainer* bits) {
uint32_t hash = 0;
auto const size = bits->MemorySize();
if (bits->bytes() == nullptr) {
// Just hash the size as a fallback if this section has no contents.
return FinalizeHash(size, 32);
}
auto const end = bits->bytes() + size;
auto const non_word_size = size % kWordSize;
auto const end_of_words =
reinterpret_cast<const uword*>(bits->bytes() + (size - non_word_size));
for (auto cursor = reinterpret_cast<const uword*>(bits->bytes());
cursor < end_of_words; cursor++) {
hash = CombineHashes(hash, *cursor);
}
for (auto cursor = reinterpret_cast<const uint8_t*>(end_of_words);
cursor < end; cursor++) {
hash = CombineHashes(hash, *cursor);
}
return FinalizeHash(hash, 32);
}
Section* Elf::GenerateFinalBuildId() {
uint32_t hashes[kBuildIdSegmentNamesLength];
for (intptr_t i = 0; i < kBuildIdSegmentNamesLength; i++) {
auto const name = kBuildIdSegmentNames[i];
auto const symbol = dynsym_->Find(name);
if (symbol == nullptr) {
// If we're missing a section, then we don't generate a final build ID.
return nullptr;
}
auto const bits = sections_[symbol->section_index]->AsBitsContainer();
if (bits == nullptr) {
FATAL1("Section for symbol %s is not a BitsContainer", name);
}
if (bits->bytes() == nullptr) {
// For now, if we don't have section contents (because we're generating
// assembly), don't generate a final build ID, as we'll have different
// build IDs in the snapshot and the separate debugging information.
//
// TODO(dartbug.com/43274): Change once we generate consistent build IDs
// between assembly snapshots and their debugging information.
return nullptr;
}
ASSERT_EQUAL(bits->MemorySize(), symbol->size);
hashes[i] = HashBitsContainer(bits);
}
// To ensure we can quickly check for a final build ID, we ensure the first
// byte contains a non-zero value.
auto const bytes = reinterpret_cast<uint8_t*>(hashes);
if (bytes[0] == 0) {
bytes[0] = 1;
}
return CreateBuildIdNote(&hashes, sizeof(hashes));
}
Section* Elf::CreateBuildIdNote(const void* description_bytes,
intptr_t description_length) {
ASSERT(description_length == 0 || description_bytes != nullptr);
ZoneWriteStream stream(zone(), kBuildIdHeaderSize + description_length);
stream.WriteFixed<decltype(elf::Note::name_size)>(sizeof(elf::ELF_NOTE_GNU));
stream.WriteFixed<decltype(elf::Note::description_size)>(description_length);
stream.WriteFixed<decltype(elf::Note::type)>(elf::NoteType::NT_GNU_BUILD_ID);
ASSERT_EQUAL(stream.Position(), sizeof(elf::Note));
stream.WriteBytes(elf::ELF_NOTE_GNU, sizeof(elf::ELF_NOTE_GNU));
ASSERT_EQUAL(stream.bytes_written(), kBuildIdHeaderSize);
stream.WriteBytes(description_bytes, description_length);
// While the build ID section does not need to be writable, it and the
// BSS section are allocated segments at the same time. Having the same flags
// ensures they will be combined in the same segment and not unnecessarily
// aligned into a new page.
return new (zone_) BitsContainer(elf::SectionHeaderType::SHT_NOTE,
/*allocate=*/true, /*executable=*/false,
/*writable=*/true, stream.bytes_written(),
stream.buffer(), kNoteAlignment);
}
void Elf::FinalizeProgramTable() {
ASSERT(program_table_file_size_ < 0);
program_table_file_offset_ = sizeof(elf::ElfHeader);
// There are two segments we need the size of the program table to create, so
// calculate it as if those two segments were already in place.
program_table_file_size_ =
(2 + segments_.length()) * sizeof(elf::ProgramHeader);
// We pre-allocated the virtual memory space for the program table itself.
// Check that we didn't generate too many segments. Currently we generate a
// fixed num of segments based on the four pieces of a snapshot, but if we
// use more in the future we'll likely need to do something more compilated
// to generate DWARF without knowing a piece's virtual address in advance.
auto const program_table_segment_size =
program_table_file_offset_ + program_table_file_size_;
RELEASE_ASSERT(program_table_segment_size < kProgramTableSegmentSize);
// Remove the original stand-in segment we added in the constructor.
segments_.EraseAt(0);
// Self-reference to program header table. Required by Android but not by
// Linux. Must appear before any PT_LOAD entries.
segments_.InsertAt(
0, new (zone_) ProgramTableSelfSegment(zone_, program_table_file_offset_,
program_table_file_size_));
// Segment for loading the initial part of the ELF file, including the
// program header table. Required by Android but not by Linux.
segments_.InsertAt(1, new (zone_) ProgramTableLoadSegment(
zone_, program_table_segment_size));
}
static const intptr_t kElfSectionTableAlignment = compiler::target::kWordSize;
void Elf::ComputeFileOffsets() {
// We calculate the size and offset of the program header table during
// finalization.
ASSERT(program_table_file_offset_ > 0 && program_table_file_size_ > 0);
intptr_t file_offset = program_table_file_offset_ + program_table_file_size_;
// When calculating file offsets for sections, we'll need to know if we've
// changed segments. Start with the one for the program table.
const auto* current_segment = segments_[1];
// The non-reserved sections are output to the file in order after the program
// header table. If we're entering a new segment, then we need to align
// according to the PT_LOAD segment alignment as well to keep the file offsets
// aligned with the memory addresses.
auto const load_align = Segment::Alignment(elf::ProgramHeaderType::PT_LOAD);
for (intptr_t i = 1; i < sections_.length(); i++) {
auto const section = sections_[i];
file_offset = Utils::RoundUp(file_offset, section->alignment);
if (section->IsAllocated() && section->load_segment != current_segment) {
file_offset = Utils::RoundUp(file_offset, load_align);
current_segment = section->load_segment;
}
section->set_file_offset(file_offset);
#if defined(DEBUG)
if (section->IsAllocated()) {
// For files that will be dynamically loaded, make sure the file offsets
// of allocated sections are page aligned to the memory offsets.
ASSERT_EQUAL(section->file_offset() % load_align,
section->memory_offset() % load_align);
}
#endif
file_offset += section->FileSize();
}
file_offset = Utils::RoundUp(file_offset, kElfSectionTableAlignment);
section_table_file_offset_ = file_offset;
section_table_file_size_ = sections_.length() * sizeof(elf::SectionHeader);
file_offset += section_table_file_size_;
}
void Elf::WriteHeader(ElfWriteStream* stream) {
#if defined(TARGET_ARCH_IS_32_BIT)
uint8_t size = elf::ELFCLASS32;
#else
uint8_t size = elf::ELFCLASS64;
#endif
uint8_t e_ident[16] = {0x7f,
'E',
'L',
'F',
size,
elf::ELFDATA2LSB,
elf::EV_CURRENT,
elf::ELFOSABI_SYSV,
0,
0,
0,
0,
0,
0,
0,
0};
stream->WriteBytes(e_ident, 16);
stream->WriteHalf(elf::ET_DYN); // Shared library.
#if defined(TARGET_ARCH_IA32)
stream->WriteHalf(elf::EM_386);
#elif defined(TARGET_ARCH_X64)
stream->WriteHalf(elf::EM_X86_64);
#elif defined(TARGET_ARCH_ARM)
stream->WriteHalf(elf::EM_ARM);
#elif defined(TARGET_ARCH_ARM64)
stream->WriteHalf(elf::EM_AARCH64);
#else
FATAL("Unknown ELF architecture");
#endif
stream->WriteWord(elf::EV_CURRENT); // Version
stream->WriteAddr(0); // "Entry point"
stream->WriteOff(program_table_file_offset_);
stream->WriteOff(section_table_file_offset_);
#if defined(TARGET_ARCH_ARM)
uword flags = elf::EF_ARM_ABI | (TargetCPUFeatures::hardfp_supported()
? elf::EF_ARM_ABI_FLOAT_HARD
: elf::EF_ARM_ABI_FLOAT_SOFT);
#else
uword flags = 0;
#endif
stream->WriteWord(flags);
stream->WriteHalf(sizeof(elf::ElfHeader));
stream->WriteHalf(sizeof(elf::ProgramHeader));
stream->WriteHalf(segments_.length());
stream->WriteHalf(sizeof(elf::SectionHeader));
stream->WriteHalf(sections_.length());
stream->WriteHalf(shstrtab_->index());
ASSERT_EQUAL(stream->Position(), sizeof(elf::ElfHeader));
}
void Elf::WriteProgramTable(ElfWriteStream* stream) {
ASSERT(program_table_file_size_ >= 0); // Check for finalization.
ASSERT(stream->Position() == program_table_file_offset_);
#if defined(DEBUG)
// Here, we count the number of times that a PT_LOAD writable segment is
// followed by a non-writable segment. We initialize last_writable to true so
// that we catch the case where the first segment is non-writable.
bool last_writable = true;
int non_writable_groups = 0;
#endif
for (auto const segment : segments_) {
#if defined(DEBUG)
if (segment->type == elf::ProgramHeaderType::PT_LOAD) {
if (last_writable && !segment->IsWritable()) {
non_writable_groups++;
}
last_writable = segment->IsWritable();
}
#endif
const intptr_t start = stream->Position();
segment->WriteProgramHeader(stream);
const intptr_t end = stream->Position();
ASSERT_EQUAL(end - start, sizeof(elf::ProgramHeader));
}
#if defined(DEBUG)
// All PT_LOAD non-writable segments must be contiguous. If not, some older
// Android dynamic linkers fail to handle writable segments between
// non-writable ones. See https://github.com/flutter/flutter/issues/43259.
ASSERT(non_writable_groups <= 1);
#endif
}
void Elf::WriteSectionTable(ElfWriteStream* stream) {
ASSERT(section_table_file_size_ >= 0); // Check for finalization.
stream->Align(kElfSectionTableAlignment);
ASSERT_EQUAL(stream->Position(), section_table_file_offset_);
for (auto const section : sections_) {
const intptr_t start = stream->Position();
section->WriteSectionHeader(stream);
const intptr_t end = stream->Position();
ASSERT_EQUAL(end - start, sizeof(elf::SectionHeader));
}
}
void Elf::WriteSections(ElfWriteStream* stream) {
ASSERT(section_table_file_size_ >= 0); // Check for finalization.
// Skip the reserved first section, as its alignment is 0 (which will cause
// stream->Align() to fail) and it never contains file contents anyway.
ASSERT_EQUAL(static_cast<uint32_t>(sections_[0]->type),
static_cast<uint32_t>(elf::SectionHeaderType::SHT_NULL));
ASSERT_EQUAL(sections_[0]->alignment, 0);
auto const load_align = Segment::Alignment(elf::ProgramHeaderType::PT_LOAD);
const Segment* current_segment = segments_[1];
for (intptr_t i = 1; i < sections_.length(); i++) {
Section* section = sections_[i];
stream->Align(section->alignment);
if (section->IsAllocated() && section->load_segment != current_segment) {
// Changing segments, so align accordingly.
stream->Align(load_align);
current_segment = section->load_segment;
}
ASSERT_EQUAL(stream->Position(), section->file_offset());
section->Write(stream);
ASSERT_EQUAL(stream->Position(),
section->file_offset() + section->FileSize());
}
}
#endif // DART_PRECOMPILER
} // namespace dart