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LibELF: Add support for loading objects with multiple data and text segments

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This enables loading executables with multiple data and text segments. Also
it fixes loading executables where the text segment has a non-zero offset.

Example:

  $ echo "main () {}" > test.c
  $ gcc -Wl,-z,separate-code -o test test.c
  $ objdump -p test
  test:     file format elf32-i386

  Program Header:
      PHDR off    0x00000034 vaddr 0x00000034 paddr 0x00000034 align 2**2
           filesz 0x000000e0 memsz 0x000000e0 flags r--
    INTERP off    0x00000114 vaddr 0x00000114 paddr 0x00000114 align 2**0
           filesz 0x00000013 memsz 0x00000013 flags r--
      LOAD off    0x00000000 vaddr 0x00000000 paddr 0x00000000 align 2**12
           filesz 0x000003c4 memsz 0x000003c4 flags r--
      LOAD off    0x00001000 vaddr 0x00001000 paddr 0x00001000 align 2**12
           filesz 0x00000279 memsz 0x00000279 flags r-x
      LOAD off    0x00002000 vaddr 0x00002000 paddr 0x00002000 align 2**12
           filesz 0x00000004 memsz 0x00000004 flags r--
      LOAD off    0x00002004 vaddr 0x00003004 paddr 0x00003004 align 2**12
           filesz 0x00000100 memsz 0x00000124 flags rw-
   DYNAMIC off    0x00002014 vaddr 0x00003014 paddr 0x00003014 align 2**2
           filesz 0x000000c8 memsz 0x000000c8 flags rw-
This commit is contained in:
Gunnar Beutner 2021-04-13 19:31:34 +02:00 • committed by Andreas Kling
parent c3ee70591a
commit cd7512a2ad
4 changed files with 121 additions and 77 deletions
Download patch file Download diff file Expand all files Collapse all files

2
Userland/Libraries/LibELF/DynamicLinker.cpp
View file

@ -276,7 +276,7 @@ void ELF::DynamicLinker::linker_main(String&& main_program_name, int main_progra
auto main_executable_loader = load_main_executable(main_program_name);
auto entry_point = main_executable_loader->image().entry();
if (main_executable_loader->is_dynamic())
entry_point = entry_point.offset(main_executable_loader->text_segment_load_address().get());
entry_point = entry_point.offset(main_executable_loader->base_address().get());
return (EntryPointFunction)(entry_point.as_ptr());
}();

169
Userland/Libraries/LibELF/DynamicLoader.cpp
View file

@ -28,6 +28,7 @@
#include <AK/Debug.h>
#include <AK/Optional.h>
#include <AK/QuickSort.h>
#include <AK/StringBuilder.h>
#include <LibELF/DynamicLinker.h>
#include <LibELF/DynamicLoader.h>
@ -167,7 +168,9 @@ RefPtr<DynamicObject> DynamicLoader::map()
load_program_headers();
m_dynamic_object = DynamicObject::create(m_text_segment_load_address, m_dynamic_section_address);
VERIFY(!m_base_address.is_null());
m_dynamic_object = DynamicObject::create(m_base_address, m_dynamic_section_address);
m_dynamic_object->set_tls_offset(m_tls_offset);
m_dynamic_object->set_tls_size(m_tls_size);
@ -184,19 +187,21 @@ bool DynamicLoader::load_stage_2(unsigned flags, size_t total_tls_size)
VERIFY(flags & RTLD_GLOBAL);
if (m_dynamic_object->has_text_relocations()) {
VERIFY(m_text_segment_load_address.get() != 0);
for (auto& text_segment : m_text_segments) {
VERIFY(text_segment.address().get() != 0);
#ifndef AK_OS_MACOS
// Remap this text region as private.
if (mremap(m_text_segment_load_address.as_ptr(), m_text_segment_size, m_text_segment_size, MAP_PRIVATE) == MAP_FAILED) {
perror("mremap .text: MAP_PRIVATE");
return false;
}
// Remap this text region as private.
if (mremap(text_segment.address().as_ptr(), text_segment.size(), text_segment.size(), MAP_PRIVATE) == MAP_FAILED) {
perror("mremap .text: MAP_PRIVATE");
return false;
}
#endif
if (0 > mprotect(m_text_segment_load_address.as_ptr(), m_text_segment_size, PROT_READ | PROT_WRITE)) {
perror("mprotect .text: PROT_READ | PROT_WRITE"); // FIXME: dlerror?
return false;
if (0 > mprotect(text_segment.address().as_ptr(), text_segment.size(), PROT_READ | PROT_WRITE)) {
perror("mprotect .text: PROT_READ | PROT_WRITE"); // FIXME: dlerror?
return false;
}
}
}
do_main_relocations(total_tls_size);
@ -230,9 +235,11 @@ RefPtr<DynamicObject> DynamicLoader::load_stage_3(unsigned flags, size_t total_t
setup_plt_trampoline();
}
if (mprotect(m_text_segment_load_address.as_ptr(), m_text_segment_size, PROT_READ | PROT_EXEC) < 0) {
perror("mprotect .text: PROT_READ | PROT_EXEC"); // FIXME: dlerror?
return nullptr;
for (auto& text_segment : m_text_segments) {
if (mprotect(text_segment.address().as_ptr(), text_segment.size(), PROT_READ | PROT_EXEC) < 0) {
perror("mprotect .text: PROT_READ | PROT_EXEC"); // FIXME: dlerror?
return nullptr;
}
}
if (m_relro_segment_size) {
@ -269,8 +276,9 @@ void DynamicLoader::do_lazy_relocations(size_t total_tls_size)
void DynamicLoader::load_program_headers()
{
Optional<ProgramHeaderRegion> text_region;
Optional<ProgramHeaderRegion> data_region;
Vector<ProgramHeaderRegion> load_regions;
Vector<ProgramHeaderRegion> text_regions;
Vector<ProgramHeaderRegion> data_regions;
Optional<ProgramHeaderRegion> tls_region;
Optional<ProgramHeaderRegion> relro_region;
@ -283,12 +291,11 @@ void DynamicLoader::load_program_headers()
VERIFY(!tls_region.has_value());
tls_region = region;
} else if (region.is_load()) {
load_regions.append(region);
if (region.is_executable()) {
VERIFY(!text_region.has_value());
text_region = region;
text_regions.append(region);
} else {
VERIFY(!data_region.has_value());
data_region = region;
data_regions.append(region);
}
} else if (region.is_dynamic()) {
dynamic_region_desired_vaddr = region.desired_load_address();
@ -299,11 +306,19 @@ void DynamicLoader::load_program_headers()
return IterationDecision::Continue;
});
VERIFY(text_region.has_value());
VERIFY(data_region.has_value());
VERIFY(!text_regions.is_empty());
VERIFY(!data_regions.is_empty());
auto compare_load_address = [](ProgramHeaderRegion& a, ProgramHeaderRegion& b) {
return a.desired_load_address().as_ptr() < b.desired_load_address().as_ptr();
};
quick_sort(load_regions, compare_load_address);
quick_sort(text_regions, compare_load_address);
quick_sort(data_regions, compare_load_address);
// Process regions in order: .text, .data, .tls
void* requested_load_address = m_elf_image.is_dynamic() ? nullptr : text_region.value().desired_load_address().as_ptr();
void* requested_load_address = m_elf_image.is_dynamic() ? nullptr : load_regions.first().desired_load_address().as_ptr();
int reservation_mmap_flags = MAP_ANON | MAP_PRIVATE | MAP_NORESERVE;
if (m_elf_image.is_dynamic())
@ -311,20 +326,16 @@ void DynamicLoader::load_program_headers()
else
reservation_mmap_flags |= MAP_FIXED;
VERIFY(!text_region.value().is_writable());
for (auto& text_region : text_regions)
VERIFY(!text_region.is_writable());
// First, we make a dummy reservation mapping, in order to allocate enough VM
// to hold both text+data contiguously in the address space.
// to hold all regions contiguously in the address space.
FlatPtr ph_text_base = text_region.value().desired_load_address().page_base().get();
FlatPtr ph_text_end = round_up_to_power_of_two(text_region.value().desired_load_address().offset(text_region.value().size_in_memory()).get(), PAGE_SIZE);
FlatPtr ph_data_base = data_region.value().desired_load_address().page_base().get();
FlatPtr ph_data_end = round_up_to_power_of_two(data_region.value().desired_load_address().offset(data_region.value().size_in_memory()).get(), PAGE_SIZE);
FlatPtr ph_load_base = load_regions.first().desired_load_address().page_base().get();
FlatPtr ph_load_end = round_up_to_power_of_two(load_regions.last().desired_load_address().offset(load_regions.last().size_in_memory()).get(), PAGE_SIZE);
size_t total_mapping_size = ph_data_end - ph_text_base;
size_t text_segment_size = ph_text_end - ph_text_base;
size_t data_segment_size = ph_data_end - ph_data_base;
size_t total_mapping_size = ph_load_end - ph_load_base;
auto* reservation = mmap(requested_load_address, total_mapping_size, PROT_NONE, reservation_mmap_flags, 0, 0);
if (reservation == MAP_FAILED) {
@ -332,68 +343,84 @@ void DynamicLoader::load_program_headers()
VERIFY_NOT_REACHED();
}
m_base_address = VirtualAddress { reservation };
// Then we unmap the reservation.
if (munmap(reservation, total_mapping_size) < 0) {
perror("munmap reservation");
VERIFY_NOT_REACHED();
}
// Now we can map the text segment at the reserved address.
auto* text_segment_begin = (u8*)mmap_with_name(
reservation,
text_segment_size,
PROT_READ,
MAP_FILE | MAP_SHARED | MAP_FIXED,
m_image_fd,
text_region.value().offset(),
String::formatted("{}: .text", m_filename).characters());
for (auto& text_region : text_regions) {
FlatPtr ph_text_base = text_region.desired_load_address().page_base().get();
FlatPtr ph_text_end = round_up_to_power_of_two(text_region.desired_load_address().offset(text_region.size_in_memory()).get(), PAGE_SIZE);
size_t text_segment_size = ph_text_end - ph_text_base;
if (text_segment_begin == MAP_FAILED) {
perror("mmap text");
VERIFY_NOT_REACHED();
auto text_segment_offset = ph_text_base - ph_load_base;
auto* text_segment_address = (u8*)reservation + text_segment_offset;
// Now we can map the text segment at the reserved address.
auto* text_segment_begin = (u8*)mmap_with_name(
text_segment_address,
text_segment_size,
PROT_READ,
MAP_FILE | MAP_SHARED | MAP_FIXED,
m_image_fd,
text_region.offset(),
String::formatted("{}: .text", m_filename).characters());
if (text_segment_begin == MAP_FAILED) {
perror("mmap text");
VERIFY_NOT_REACHED();
}
m_text_segments.append({ VirtualAddress { (FlatPtr)text_segment_begin }, text_segment_size });
}
VERIFY(requested_load_address == nullptr || requested_load_address == text_segment_begin);
m_text_segment_size = text_segment_size;
m_text_segment_load_address = VirtualAddress { (FlatPtr)text_segment_begin };
VERIFY(requested_load_address == nullptr || requested_load_address == reservation);
if (relro_region.has_value()) {
m_relro_segment_size = relro_region->size_in_memory();
m_relro_segment_address = m_text_segment_load_address.offset(relro_region->desired_load_address().get());
m_relro_segment_address = VirtualAddress { (u8*)reservation + relro_region->desired_load_address().get() };
}
if (m_elf_image.is_dynamic())
m_dynamic_section_address = dynamic_region_desired_vaddr.offset(m_text_segment_load_address.get());
m_dynamic_section_address = VirtualAddress { (u8*)reservation + dynamic_region_desired_vaddr.get() };
else
m_dynamic_section_address = dynamic_region_desired_vaddr;
FlatPtr data_segment_offset_from_text = ph_data_base - ph_text_base;
for (auto& data_region : data_regions) {
FlatPtr ph_data_base = data_region.desired_load_address().page_base().get();
FlatPtr ph_data_end = round_up_to_power_of_two(data_region.desired_load_address().offset(data_region.size_in_memory()).get(), PAGE_SIZE);
size_t data_segment_size = ph_data_end - ph_data_base;
// Finally, we make an anonymous mapping for the data segment. Contents are then copied from the file.
auto* data_segment_address = (u8*)text_segment_begin + data_segment_offset_from_text;
auto data_segment_offset = ph_data_base - ph_load_base;
auto* data_segment_address = (u8*)reservation + data_segment_offset;
auto* data_segment = (u8*)mmap_with_name(
data_segment_address,
data_segment_size,
PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED,
0,
0,
String::formatted("{}: .data", m_filename).characters());
// Finally, we make an anonymous mapping for the data segment. Contents are then copied from the file.
auto* data_segment = (u8*)mmap_with_name(
data_segment_address,
data_segment_size,
PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED,
0,
0,
String::formatted("{}: .data", m_filename).characters());
if (MAP_FAILED == data_segment) {
perror("mmap data");
VERIFY_NOT_REACHED();
if (MAP_FAILED == data_segment) {
perror("mmap data");
VERIFY_NOT_REACHED();
}
VirtualAddress data_segment_start;
if (m_elf_image.is_dynamic())
data_segment_start = VirtualAddress { (u8*)reservation + data_region.desired_load_address().get() };
else
data_segment_start = data_region.desired_load_address();
memcpy(data_segment_start.as_ptr(), (u8*)m_file_data + data_region.offset(), data_region.size_in_image());
}
VirtualAddress data_segment_start;
if (m_elf_image.is_dynamic())
data_segment_start = data_region.value().desired_load_address().offset((FlatPtr)text_segment_begin);
else
data_segment_start = data_region.value().desired_load_address();
memcpy(data_segment_start.as_ptr(), (u8*)m_file_data + data_region.value().offset(), data_region.value().size_in_image());
// FIXME: Initialize the values in the TLS section. Currently, it is zeroed.
}

23
Userland/Libraries/LibELF/DynamicLoader.h
View file

@ -38,6 +38,22 @@
namespace ELF {
class LoadedSegment {
public:
LoadedSegment(VirtualAddress address, size_t size)
: m_address(address)
, m_size(size)
{
}
VirtualAddress address() const { return m_address; }
size_t size() const { return m_size; }
private:
VirtualAddress m_address;
size_t m_size;
};
class DynamicLoader : public RefCounted<DynamicLoader> {
public:
static RefPtr<DynamicLoader> try_create(int fd, String filename);
@ -74,7 +90,8 @@ public:
template<typename F>
void for_each_needed_library(F) const;
VirtualAddress text_segment_load_address() const { return m_text_segment_load_address; }
VirtualAddress base_address() const { return m_base_address; }
const Vector<LoadedSegment> text_segments() const { return m_text_segments; }
bool is_dynamic() const { return m_elf_image.is_dynamic(); }
static Optional<DynamicObject::SymbolLookupResult> lookup_symbol(const ELF::DynamicObject::Symbol&);
@ -141,8 +158,8 @@ private:
RefPtr<DynamicObject> m_dynamic_object;
VirtualAddress m_text_segment_load_address;
size_t m_text_segment_size { 0 };
VirtualAddress m_base_address;
Vector<LoadedSegment> m_text_segments;
VirtualAddress m_relro_segment_address;
size_t m_relro_segment_size { 0 };

4
Userland/Libraries/LibELF/DynamicObject.cpp
View file

@ -38,9 +38,9 @@ namespace ELF {
static const char* name_for_dtag(Elf32_Sword d_tag);
DynamicObject::DynamicObject(VirtualAddress base_address, VirtualAddress dynamic_section_addresss)
DynamicObject::DynamicObject(VirtualAddress base_address, VirtualAddress dynamic_section_address)
: m_base_address(base_address)
, m_dynamic_address(dynamic_section_addresss)
, m_dynamic_address(dynamic_section_address)
{
auto* header = (Elf32_Ehdr*)base_address.as_ptr();
auto* pheader = (Elf32_Phdr*)(base_address.as_ptr() + header->e_phoff);