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More linker cleanup.

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Change-Id: I9fb3c7c0d4b4ffef0eeaf092d4e30ffe63a08671
This commit is contained in:
Elliott Hughes
2013-03-05 18:47:58 -08:00
parent 036f909720
commit 650be4e584
6 changed files with 326 additions and 466 deletions
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482
linker/linker_phdr.cpp
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@@ -26,10 +26,13 @@
* SUCH DAMAGE.
*/
#include "linker_phdr.h"
#include <errno.h>
#include <sys/mman.h>
#include "linker_phdr.h"
#include "linker.h"
#include "linker_debug.h"
/**
TECHNICAL NOTE ON ELF LOADING.
@@ -112,66 +115,116 @@
MAYBE_MAP_FLAG((x), PF_R, PROT_READ) | \
MAYBE_MAP_FLAG((x), PF_W, PROT_WRITE))
/* Load the program header table from an ELF file into a read-only private
* anonymous mmap-ed block.
*
* Input:
* fd -> file descriptor
* phdr_offset -> file offset of phdr table
* phdr_num -> number of entries in the table.
*
* Output:
* phdr_mmap -> address of mmap block in memory.
* phdr_memsize -> size of mmap block in memory.
* phdr_table -> address of first entry in memory.
*
* Return:
* -1 on error, or 0 on success.
*/
int phdr_table_load(int fd,
Elf32_Addr phdr_offset,
Elf32_Half phdr_num,
void** phdr_mmap,
Elf32_Addr* phdr_size,
const Elf32_Phdr** phdr_table)
{
Elf32_Addr page_min, page_max, page_offset;
void* mmap_result;
/* Just like the kernel, we only accept program header tables that
* are smaller than 64KB. */
if (phdr_num < 1 || phdr_num > 65536/sizeof(Elf32_Phdr)) {
errno = EINVAL;
return -1;
}
page_min = PAGE_START(phdr_offset);
page_max = PAGE_END(phdr_offset + phdr_num*sizeof(Elf32_Phdr));
page_offset = PAGE_OFFSET(phdr_offset);
mmap_result = mmap(NULL,
page_max - page_min,
PROT_READ,
MAP_PRIVATE,
fd,
page_min);
if (mmap_result == MAP_FAILED) {
return -1;
}
*phdr_mmap = mmap_result;
*phdr_size = page_max - page_min;
*phdr_table = (Elf32_Phdr*)((char*)mmap_result + page_offset);
return 0;
ElfReader::ElfReader(const char* name, int fd)
: name_(name), fd_(fd),
phdr_num_(0), phdr_mmap_(NULL), phdr_table_(NULL), phdr_size_(0),
load_start_(NULL), load_size_(0), load_bias_(0),
loaded_phdr_(NULL) {
}
void phdr_table_unload(void* phdr_mmap, Elf32_Addr phdr_memsize)
{
munmap(phdr_mmap, phdr_memsize);
ElfReader::~ElfReader() {
if (fd_ != -1) {
close(fd_);
}
if (phdr_mmap_ != NULL) {
munmap(phdr_mmap_, phdr_size_);
}
}
bool ElfReader::Load() {
return ReadElfHeader() &&
VerifyElfHeader() &&
ReadProgramHeader() &&
ReserveAddressSpace() &&
LoadSegments() &&
FindPhdr();
}
bool ElfReader::ReadElfHeader() {
ssize_t rc = TEMP_FAILURE_RETRY(read(fd_, &header_, sizeof(header_)));
if (rc < 0) {
DL_ERR("can't read file \"%s\": %s", name_, strerror(errno));
return false;
}
if (rc != sizeof(header_)) {
DL_ERR("\"%s\" is too small to be an ELF executable", name_);
return false;
}
return true;
}
bool ElfReader::VerifyElfHeader() {
if (header_.e_ident[EI_MAG0] != ELFMAG0 ||
header_.e_ident[EI_MAG1] != ELFMAG1 ||
header_.e_ident[EI_MAG2] != ELFMAG2 ||
header_.e_ident[EI_MAG3] != ELFMAG3) {
DL_ERR("\"%s\" has bad ELF magic", name_);
return false;
}
if (header_.e_ident[EI_CLASS] != ELFCLASS32) {
DL_ERR("\"%s\" not 32-bit: %d", name_, header_.e_ident[EI_CLASS]);
return false;
}
if (header_.e_ident[EI_DATA] != ELFDATA2LSB) {
DL_ERR("\"%s\" not little-endian: %d", name_, header_.e_ident[EI_DATA]);
return false;
}
if (header_.e_type != ET_DYN) {
DL_ERR("\"%s\" has unexpected e_type: %d", name_, header_.e_type);
return false;
}
if (header_.e_version != EV_CURRENT) {
DL_ERR("\"%s\" has unexpected e_version: %d", name_, header_.e_version);
return false;
}
if (header_.e_machine !=
#ifdef ANDROID_ARM_LINKER
EM_ARM
#elif defined(ANDROID_MIPS_LINKER)
EM_MIPS
#elif defined(ANDROID_X86_LINKER)
EM_386
#endif
) {
DL_ERR("\"%s\" has unexpected e_machine: %d", name_, header_.e_machine);
return false;
}
return true;
}
// Loads the program header table from an ELF file into a read-only private
// anonymous mmap-ed block.
bool ElfReader::ReadProgramHeader() {
phdr_num_ = header_.e_phnum;
// Like the kernel, we only accept program header tables that
// are smaller than 64KiB.
if (phdr_num_ < 1 || phdr_num_ > 65536/sizeof(Elf32_Phdr)) {
DL_ERR("\"%s\" has invalid e_phnum: %d", name_, phdr_num_);
return false;
}
Elf32_Addr page_min = PAGE_START(header_.e_phoff);
Elf32_Addr page_max = PAGE_END(header_.e_phoff + (phdr_num_ * sizeof(Elf32_Phdr)));
Elf32_Addr page_offset = PAGE_OFFSET(header_.e_phoff);
phdr_size_ = page_max - page_min;
void* mmap_result = mmap(NULL, phdr_size_, PROT_READ, MAP_PRIVATE, fd_, page_min);
if (mmap_result == MAP_FAILED) {
DL_ERR("\"%s\" phdr mmap failed: %s", name_, strerror(errno));
return false;
}
phdr_mmap_ = mmap_result;
phdr_table_ = reinterpret_cast<Elf32_Phdr*>(reinterpret_cast<char*>(mmap_result) + page_offset);
return true;
}
/* Compute the extent of all loadable segments in an ELF program header
* table. This corresponds to the page-aligned size in bytes that needs to be
@@ -211,134 +264,100 @@ Elf32_Addr phdr_table_get_load_size(const Elf32_Phdr* phdr_table,
return max_vaddr - min_vaddr;
}
/* Reserve a virtual address range big enough to hold all loadable
* segments of a program header table. This is done by creating a
* private anonymous mmap() with PROT_NONE.
*
* Input:
* phdr_table -> program header table
* phdr_count -> number of entries in the tables
* Output:
* load_start -> first page of reserved address space range
* load_size -> size in bytes of reserved address space range
* load_bias -> load bias, as described in technical note above.
*
* Return:
* 0 on success, -1 otherwise. Error code in errno.
*/
int
phdr_table_reserve_memory(const Elf32_Phdr* phdr_table,
size_t phdr_count,
void** load_start,
Elf32_Addr* load_size,
Elf32_Addr* load_bias)
{
Elf32_Addr size = phdr_table_get_load_size(phdr_table, phdr_count);
if (size == 0) {
errno = EINVAL;
return -1;
}
// Reserve a virtual address range big enough to hold all loadable
// segments of a program header table. This is done by creating a
// private anonymous mmap() with PROT_NONE.
bool ElfReader::ReserveAddressSpace() {
load_size_ = phdr_table_get_load_size(phdr_table_, phdr_num_);
if (load_size_ == 0) {
DL_ERR("\"%s\" has no loadable segments", name_);
return false;
}
int mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS;
void* start = mmap(NULL, size, PROT_NONE, mmap_flags, -1, 0);
if (start == MAP_FAILED) {
return -1;
}
int mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS;
void* start = mmap(NULL, load_size_, PROT_NONE, mmap_flags, -1, 0);
if (start == MAP_FAILED) {
DL_ERR("couldn't reserve %d bytes of address space for \"%s\"", load_size_, name_);
return false;
}
*load_start = start;
*load_size = size;
*load_bias = 0;
load_start_ = start;
load_bias_ = 0;
for (size_t i = 0; i < phdr_count; ++i) {
const Elf32_Phdr* phdr = &phdr_table[i];
if (phdr->p_type == PT_LOAD) {
*load_bias = (Elf32_Addr)start - PAGE_START(phdr->p_vaddr);
break;
}
for (size_t i = 0; i < phdr_num_; ++i) {
const Elf32_Phdr* phdr = &phdr_table_[i];
if (phdr->p_type == PT_LOAD) {
load_bias_ = reinterpret_cast<Elf32_Addr>(start) - PAGE_START(phdr->p_vaddr);
break;
}
return 0;
}
return true;
}
/* Map all loadable segments in process' address space.
* This assumes you already called phdr_table_reserve_memory to
* reserve the address space range for the library.
*
* Input:
* phdr_table -> program header table
* phdr_count -> number of entries in the table
* load_bias -> load offset.
* fd -> input file descriptor.
*
* Return:
* 0 on success, -1 otherwise. Error code in errno.
*/
int
phdr_table_load_segments(const Elf32_Phdr* phdr_table,
int phdr_count,
Elf32_Addr load_bias,
int fd)
{
int nn;
// Map all loadable segments in process' address space.
// This assumes you already called phdr_table_reserve_memory to
// reserve the address space range for the library.
// TODO: assert assumption.
bool ElfReader::LoadSegments() {
for (size_t i = 0; i < phdr_num_; ++i) {
const Elf32_Phdr* phdr = &phdr_table_[i];
for (nn = 0; nn < phdr_count; nn++) {
const Elf32_Phdr* phdr = &phdr_table[nn];
void* seg_addr;
if (phdr->p_type != PT_LOAD)
continue;
/* Segment addresses in memory */
Elf32_Addr seg_start = phdr->p_vaddr + load_bias;
Elf32_Addr seg_end = seg_start + phdr->p_memsz;
Elf32_Addr seg_page_start = PAGE_START(seg_start);
Elf32_Addr seg_page_end = PAGE_END(seg_end);
Elf32_Addr seg_file_end = seg_start + phdr->p_filesz;
/* File offsets */
Elf32_Addr file_start = phdr->p_offset;
Elf32_Addr file_end = file_start + phdr->p_filesz;
Elf32_Addr file_page_start = PAGE_START(file_start);
seg_addr = mmap((void*)seg_page_start,
file_end - file_page_start,
PFLAGS_TO_PROT(phdr->p_flags),
MAP_FIXED|MAP_PRIVATE,
fd,
file_page_start);
if (seg_addr == MAP_FAILED) {
return -1;
}
/* if the segment is writable, and does not end on a page boundary,
* zero-fill it until the page limit. */
if ((phdr->p_flags & PF_W) != 0 && PAGE_OFFSET(seg_file_end) > 0) {
memset((void*)seg_file_end, 0, PAGE_SIZE - PAGE_OFFSET(seg_file_end));
}
seg_file_end = PAGE_END(seg_file_end);
/* seg_file_end is now the first page address after the file
* content. If seg_end is larger, we need to zero anything
* between them. This is done by using a private anonymous
* map for all extra pages.
*/
if (seg_page_end > seg_file_end) {
void* zeromap = mmap((void*)seg_file_end,
seg_page_end - seg_file_end,
PFLAGS_TO_PROT(phdr->p_flags),
MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE,
-1,
0);
if (zeromap == MAP_FAILED) {
return -1;
}
}
if (phdr->p_type != PT_LOAD) {
continue;
}
return 0;
// Segment addresses in memory.
Elf32_Addr seg_start = phdr->p_vaddr + load_bias_;
Elf32_Addr seg_end = seg_start + phdr->p_memsz;
Elf32_Addr seg_page_start = PAGE_START(seg_start);
Elf32_Addr seg_page_end = PAGE_END(seg_end);
Elf32_Addr seg_file_end = seg_start + phdr->p_filesz;
// File offsets.
Elf32_Addr file_start = phdr->p_offset;
Elf32_Addr file_end = file_start + phdr->p_filesz;
Elf32_Addr file_page_start = PAGE_START(file_start);
void* seg_addr = mmap((void*)seg_page_start,
file_end - file_page_start,
PFLAGS_TO_PROT(phdr->p_flags),
MAP_FIXED|MAP_PRIVATE,
fd_,
file_page_start);
if (seg_addr == MAP_FAILED) {
DL_ERR("couldn't map \"%s\" segment %d: %s", name_, i, strerror(errno));
return false;
}
// if the segment is writable, and does not end on a page boundary,
// zero-fill it until the page limit.
if ((phdr->p_flags & PF_W) != 0 && PAGE_OFFSET(seg_file_end) > 0) {
memset((void*)seg_file_end, 0, PAGE_SIZE - PAGE_OFFSET(seg_file_end));
}
seg_file_end = PAGE_END(seg_file_end);
// seg_file_end is now the first page address after the file
// content. If seg_end is larger, we need to zero anything
// between them. This is done by using a private anonymous
// map for all extra pages.
if (seg_page_end > seg_file_end) {
void* zeromap = mmap((void*)seg_file_end,
seg_page_end - seg_file_end,
PFLAGS_TO_PROT(phdr->p_flags),
MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE,
-1,
0);
if (zeromap == MAP_FAILED) {
DL_ERR("couldn't zero fill \"%s\" gap: %s", name_, strerror(errno));
return false;
}
}
}
return true;
}
/* Used internally. Used to set the protection bits of all loaded segments
@@ -577,72 +596,55 @@ phdr_table_get_dynamic_section(const Elf32_Phdr* phdr_table,
}
}
/* Return the address of the program header table as it appears in the loaded
* segments in memory. This is in contrast with the input 'phdr_table' which
* is temporary and will be released before the library is relocated.
*
* Input:
* phdr_table -> program header table
* phdr_count -> number of entries in tables
* load_bias -> load bias
* Return:
* Address of loaded program header table on success (it has
* 'phdr_count' entries), or NULL on failure (no error code).
*/
const Elf32_Phdr*
phdr_table_get_loaded_phdr(const Elf32_Phdr* phdr_table,
int phdr_count,
Elf32_Addr load_bias)
{
const Elf32_Phdr* phdr = phdr_table;
const Elf32_Phdr* phdr_limit = phdr + phdr_count;
Elf32_Addr loaded = 0;
Elf32_Addr loaded_end;
// Returns the address of the program header table as it appears in the loaded
// segments in memory. This is in contrast with 'phdr_table_' which
// is temporary and will be released before the library is relocated.
bool ElfReader::FindPhdr() {
const Elf32_Phdr* phdr_limit = phdr_table_ + phdr_num_;
/* If there is a PT_PHDR, use it directly */
for (phdr = phdr_table; phdr < phdr_limit; phdr++) {
if (phdr->p_type == PT_PHDR) {
loaded = load_bias + phdr->p_vaddr;
goto CHECK;
}
// If there is a PT_PHDR, use it directly.
for (const Elf32_Phdr* phdr = phdr_table_; phdr < phdr_limit; ++phdr) {
if (phdr->p_type == PT_PHDR) {
return CheckPhdr(load_bias_ + phdr->p_vaddr);
}
}
/* Otherwise, check the first loadable segment. If its file offset
* is 0, it starts with the ELF header, and we can trivially find the
* loaded program header from it. */
for (phdr = phdr_table; phdr < phdr_limit; phdr++) {
if (phdr->p_type == PT_LOAD) {
if (phdr->p_offset == 0) {
Elf32_Addr elf_addr = load_bias + phdr->p_vaddr;
const Elf32_Ehdr* ehdr = (const Elf32_Ehdr*)(void*)elf_addr;
Elf32_Addr offset = ehdr->e_phoff;
loaded = (Elf32_Addr)ehdr + offset;
goto CHECK;
}
break;
}
// Otherwise, check the first loadable segment. If its file offset
// is 0, it starts with the ELF header, and we can trivially find the
// loaded program header from it.
for (const Elf32_Phdr* phdr = phdr_table_; phdr < phdr_limit; ++phdr) {
if (phdr->p_type == PT_LOAD) {
if (phdr->p_offset == 0) {
Elf32_Addr elf_addr = load_bias_ + phdr->p_vaddr;
const Elf32_Ehdr* ehdr = (const Elf32_Ehdr*)(void*)elf_addr;
Elf32_Addr offset = ehdr->e_phoff;
return CheckPhdr((Elf32_Addr)ehdr + offset);
}
break;
}
}
/* We didn't find it, let the client know. He may be able to
* keep a copy of the input phdr_table instead. */
return NULL;
CHECK:
/* Ensure that our program header is actually within a loadable
* segment. This should help catch badly-formed ELF files that
* would cause the linker to crash later when trying to access it.
*/
loaded_end = loaded + phdr_count*sizeof(Elf32_Phdr);
for (phdr = phdr_table; phdr < phdr_limit; phdr++) {
if (phdr->p_type != PT_LOAD)
continue;
Elf32_Addr seg_start = phdr->p_vaddr + load_bias;
Elf32_Addr seg_end = phdr->p_filesz + seg_start;
if (seg_start <= loaded && loaded_end <= seg_end) {
return (const Elf32_Phdr*)loaded;
}
}
return NULL;
DL_ERR("can't find loaded phdr for \"%s\"", name_);
return false;
}
// Ensures that our program header is actually within a loadable
// segment. This should help catch badly-formed ELF files that
// would cause the linker to crash later when trying to access it.
bool ElfReader::CheckPhdr(Elf32_Addr loaded) {
const Elf32_Phdr* phdr_limit = phdr_table_ + phdr_num_;
Elf32_Addr loaded_end = loaded + (phdr_num_ * sizeof(Elf32_Phdr));
for (Elf32_Phdr* phdr = phdr_table_; phdr < phdr_limit; ++phdr) {
if (phdr->p_type != PT_LOAD) {
continue;
}
Elf32_Addr seg_start = phdr->p_vaddr + load_bias_;
Elf32_Addr seg_end = phdr->p_filesz + seg_start;
if (seg_start <= loaded && loaded_end <= seg_end) {
loaded_phdr_ = reinterpret_cast<const Elf32_Phdr*>(loaded);
return true;
}
}
DL_ERR("\"%s\" loaded phdr %x not in loadable segment", name_, loaded);
return false;
}