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// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/debug/test_elf_image_builder.h"
#include <cstring>
#include <type_traits>
#include <utility>
#include "base/bits.h"
#include "base/check.h"
#include "base/notreached.h"
#include "build/build_config.h"
#if __SIZEOF_POINTER__ == 4
using Dyn = Elf32_Dyn;
using Nhdr = Elf32_Nhdr;
using Shdr = Elf32_Shdr;
#else
using Dyn = Elf64_Dyn;
using Nhdr = Elf64_Nhdr;
using Shdr = Elf64_Shdr;
#endif
namespace base {
namespace {
// Sizes/alignments to use in the ELF image.
static constexpr size_t kPageSize = 4096;
static constexpr size_t kPhdrAlign = 0x4;
static constexpr size_t kNoteAlign = 0x4;
static constexpr size_t kLoadAlign = 0x1000;
static constexpr size_t kDynamicAlign = 0x4;
} // namespace
struct TestElfImageBuilder::LoadSegment {
Word flags;
Word size;
};
TestElfImage::TestElfImage(std::vector<uint8_t> buffer, const void* elf_start)
: buffer_(std::move(buffer)), elf_start_(elf_start) {}
TestElfImage::~TestElfImage() = default;
TestElfImage::TestElfImage(TestElfImage&&) = default;
TestElfImage& TestElfImage::operator=(TestElfImage&&) = default;
TestElfImageBuilder::TestElfImageBuilder(MappingType mapping_type)
: mapping_type_(mapping_type) {}
TestElfImageBuilder::~TestElfImageBuilder() = default;
TestElfImageBuilder& TestElfImageBuilder::AddLoadSegment(Word flags,
size_t size) {
load_segments_.push_back({flags, static_cast<Word>(size)});
return *this;
}
TestElfImageBuilder& TestElfImageBuilder::AddNoteSegment(
Word type,
StringPiece name,
span<const uint8_t> desc) {
const size_t name_with_null_size = name.size() + 1;
std::vector<uint8_t> buffer(
sizeof(Nhdr) + bits::AlignUp(name_with_null_size, size_t{4}) +
bits::AlignUp(desc.size(), size_t{4}),
'\0');
uint8_t* loc = &buffer.front();
Nhdr nhdr;
nhdr.n_namesz = name_with_null_size;
nhdr.n_descsz = desc.size();
nhdr.n_type = type;
loc = AppendHdr(nhdr, loc);
memcpy(loc, name.data(), name.size());
*(loc + name.size()) = '\0';
loc += bits::AlignUp(name_with_null_size, size_t{4});
memcpy(loc, &desc.front(), desc.size());
loc += bits::AlignUp(desc.size(), size_t{4});
DCHECK_EQ(&buffer.front() + buffer.size(), loc);
note_contents_.push_back(std::move(buffer));
return *this;
}
TestElfImageBuilder& TestElfImageBuilder::AddSoName(StringPiece soname) {
DCHECK(!soname_.has_value());
soname_.emplace(soname);
return *this;
}
struct TestElfImageBuilder::ImageMeasures {
size_t phdrs_required;
size_t note_start;
size_t note_size;
std::vector<size_t> load_segment_start;
size_t dynamic_start;
size_t strtab_start;
size_t total_size;
};
Addr TestElfImageBuilder::GetVirtualAddressForOffset(
Off offset,
const uint8_t* elf_start) const {
switch (mapping_type_) {
case RELOCATABLE:
return static_cast<Addr>(offset);
case RELOCATABLE_WITH_BIAS:
return static_cast<Addr>(offset + kLoadBias);
case NON_RELOCATABLE:
return reinterpret_cast<Addr>(elf_start + offset);
}
}
TestElfImageBuilder::ImageMeasures TestElfImageBuilder::MeasureSizesAndOffsets()
const {
ImageMeasures measures;
measures.phdrs_required = 1 + load_segments_.size();
if (!note_contents_.empty())
++measures.phdrs_required;
if (soname_.has_value())
++measures.phdrs_required;
// The current offset into the image, where the next bytes are to be written.
// Starts after the ELF header.
size_t offset = sizeof(Ehdr);
// Add space for the program header table.
offset = bits::AlignUp(offset, kPhdrAlign);
offset += sizeof(Phdr) * measures.phdrs_required;
// Add space for the notes.
measures.note_start = offset;
if (!note_contents_.empty())
offset = bits::AlignUp(offset, kNoteAlign);
for (const std::vector<uint8_t>& contents : note_contents_)
offset += contents.size();
measures.note_size = offset - measures.note_start;
// Add space for the load segments.
for (auto it = load_segments_.begin(); it != load_segments_.end(); ++it) {
// The first non PT_PHDR program header is expected to be a PT_LOAD and
// start at the already-aligned start of the ELF header.
if (it == load_segments_.begin()) {
measures.load_segment_start.push_back(0);
} else {
offset = bits::AlignUp(offset, kLoadAlign);
measures.load_segment_start.push_back(offset);
}
offset += it->size;
}
// Add space for the dynamic segment.
measures.dynamic_start = bits::AlignUp(offset, kDynamicAlign);
offset += sizeof(Dyn) * (soname_ ? 2 : 1);
measures.strtab_start = offset;
// Add space for the string table.
++offset; // The first string table byte holds a null character.
if (soname_)
offset += soname_->size() + 1;
measures.total_size = offset;
return measures;
}
TestElfImage TestElfImageBuilder::Build() {
ImageMeasures measures = MeasureSizesAndOffsets();
// Write the ELF contents into |buffer|. Extends the buffer back to the 0
// address in the case of load bias, so that the memory between the 0 address
// and the image start is zero-initialized.
const size_t load_bias =
mapping_type_ == RELOCATABLE_WITH_BIAS ? kLoadBias : 0;
std::vector<uint8_t> buffer(load_bias + (kPageSize - 1) + measures.total_size,
'\0');
uint8_t* const elf_start =
bits::AlignUp(&buffer.front() + load_bias, kPageSize);
uint8_t* loc = elf_start;
// Add the ELF header.
loc = AppendHdr(CreateEhdr(measures.phdrs_required), loc);
// Add the program header table.
loc = bits::AlignUp(loc, kPhdrAlign);
loc = AppendHdr(
CreatePhdr(PT_PHDR, PF_R, kPhdrAlign, loc - elf_start,
GetVirtualAddressForOffset(loc - elf_start, elf_start),
sizeof(Phdr) * measures.phdrs_required),
loc);
for (size_t i = 0; i < load_segments_.size(); ++i) {
const LoadSegment& load_segment = load_segments_[i];
size_t size = load_segment.size;
// The first non PT_PHDR program header is expected to be a PT_LOAD and
// encompass all the preceding headers.
if (i == 0)
size += loc - elf_start;
loc = AppendHdr(CreatePhdr(PT_LOAD, load_segment.flags, kLoadAlign,
measures.load_segment_start[i],
GetVirtualAddressForOffset(
measures.load_segment_start[i], elf_start),
size),
loc);
}
if (measures.note_size != 0) {
loc = AppendHdr(
CreatePhdr(PT_NOTE, PF_R, kNoteAlign, measures.note_start,
GetVirtualAddressForOffset(measures.note_start, elf_start),
measures.note_size),
loc);
}
if (soname_) {
loc = AppendHdr(
CreatePhdr(
PT_DYNAMIC, PF_R | PF_W, kDynamicAlign, measures.dynamic_start,
GetVirtualAddressForOffset(measures.dynamic_start, elf_start),
sizeof(Dyn) * 2),
loc);
}
// Add the notes.
loc = bits::AlignUp(loc, kNoteAlign);
for (const std::vector<uint8_t>& contents : note_contents_) {
memcpy(loc, &contents.front(), contents.size());
loc += contents.size();
}
// Add the load segments.
for (auto it = load_segments_.begin(); it != load_segments_.end(); ++it) {
if (it != load_segments_.begin())
loc = bits::AlignUp(loc, kLoadAlign);
memset(loc, 0, it->size);
loc += it->size;
}
loc = bits::AlignUp(loc, kDynamicAlign);
// Add the soname state.
if (soname_) {
// Add a DYNAMIC section for the soname.
Dyn soname_dyn;
soname_dyn.d_tag = DT_SONAME;
soname_dyn.d_un.d_val = 1; // One char into the string table.
loc = AppendHdr(soname_dyn, loc);
}
Dyn strtab_dyn;
strtab_dyn.d_tag = DT_STRTAB;
#if BUILDFLAG(IS_FUCHSIA) || BUILDFLAG(IS_ANDROID)
// Fuchsia and Android do not alter the symtab pointer on ELF load -- it's
// expected to remain a 'virutal address'.
strtab_dyn.d_un.d_ptr =
GetVirtualAddressForOffset(measures.strtab_start, elf_start);
#else
// Linux relocates this value on ELF load, so produce the pointer value after
// relocation. That value will always be equal to the actual memory address.
strtab_dyn.d_un.d_ptr =
reinterpret_cast<uintptr_t>(elf_start + measures.strtab_start);
#endif
loc = AppendHdr(strtab_dyn, loc);
// Add a string table with one entry for the soname, if necessary.
*loc++ = '\0'; // The first byte holds a null character.
if (soname_) {
memcpy(loc, soname_->data(), soname_->size());
*(loc + soname_->size()) = '\0';
loc += soname_->size() + 1;
}
// The offset past the end of the contents should be consistent with the size
// mmeasurement above.
DCHECK_EQ(loc, elf_start + measures.total_size);
return TestElfImage(std::move(buffer), elf_start);
}
// static
template <typename T>
uint8_t* TestElfImageBuilder::AppendHdr(const T& hdr, uint8_t* loc) {
static_assert(std::is_trivially_copyable_v<T>, "T should be a plain struct");
memcpy(loc, &hdr, sizeof(T));
return loc + sizeof(T);
}
Ehdr TestElfImageBuilder::CreateEhdr(Half phnum) {
Ehdr ehdr;
ehdr.e_ident[EI_MAG0] = ELFMAG0;
ehdr.e_ident[EI_MAG1] = ELFMAG1;
ehdr.e_ident[EI_MAG2] = ELFMAG2;
ehdr.e_ident[EI_MAG3] = ELFMAG3;
ehdr.e_ident[EI_CLASS] = __SIZEOF_POINTER__ == 4 ? 1 : 2;
ehdr.e_ident[EI_DATA] = 1; // Little endian.
ehdr.e_ident[EI_VERSION] = 1;
ehdr.e_ident[EI_OSABI] = 0x00;
ehdr.e_ident[EI_ABIVERSION] = 0;
ehdr.e_ident[EI_PAD] = 0;
ehdr.e_type = ET_DYN;
ehdr.e_machine = 0x28; // ARM.
ehdr.e_version = 1;
ehdr.e_entry = 0;
ehdr.e_phoff = sizeof(Ehdr);
ehdr.e_shoff = 0;
ehdr.e_flags = 0;
ehdr.e_ehsize = sizeof(Ehdr);
ehdr.e_phentsize = sizeof(Phdr);
ehdr.e_phnum = phnum;
ehdr.e_shentsize = sizeof(Shdr);
ehdr.e_shnum = 0;
ehdr.e_shstrndx = 0;
return ehdr;
}
Phdr TestElfImageBuilder::CreatePhdr(Word type,
Word flags,
size_t align,
Off offset,
Addr vaddr,
size_t size) {
Phdr phdr;
phdr.p_type = type;
phdr.p_flags = flags;
phdr.p_offset = offset;
phdr.p_filesz = size;
phdr.p_vaddr = vaddr;
phdr.p_paddr = 0;
phdr.p_memsz = phdr.p_filesz;
phdr.p_align = align;
return phdr;
}
} // namespace base
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