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#include "ELFLoader.h"
#include <AK/kstdio.h>
//#define ELFLOADER_DEBUG
ELFLoader::ELFLoader(const byte* buffer)
: m_image(buffer)
{
}
ELFLoader::~ELFLoader()
{
}
bool ELFLoader::load()
{
#ifdef ELFLOADER_DEBUG
m_image.dump();
#endif
if (!m_image.is_valid())
return false;
if (!layout())
return false;
export_symbols();
if (!perform_relocations())
return false;
return true;
}
bool ELFLoader::layout()
{
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Layout\n");
#endif
bool failed = false;
m_image.for_each_program_header([&] (const ELFImage::ProgramHeader& program_header) {
if (program_header.type() != PT_LOAD)
return;
#ifdef ELFLOADER_DEBUG
kprintf("PH: L%x %u r:%u w:%u\n", program_header.laddr().get(), program_header.size_in_memory(), program_header.is_readable(), program_header.is_writable());
#endif
if (program_header.is_writable()) {
allocate_section(program_header.laddr(), program_header.size_in_memory(), program_header.alignment(), program_header.is_readable(), program_header.is_writable());
} else {
map_section(program_header.laddr(), program_header.size_in_memory(), program_header.alignment(), program_header.offset(), program_header.is_readable(), program_header.is_writable());
}
});
m_image.for_each_section_of_type(SHT_PROGBITS, [this] (const ELFImage::Section& section) {
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Copying progbits section: %s\n", section.name());
#endif
if (!section.size())
return true;
char* ptr = (char*)section.address();
if (!ptr) {
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: ignoring section '%s' with null address\n", section.name());
#endif
return true;
}
memcpy(ptr, section.raw_data(), section.size());
m_sections.set(section.name(), move(ptr));
return true;
});
m_image.for_each_section_of_type(SHT_NOBITS, [this, &failed] (const ELFImage::Section& section) {
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Copying nobits section: %s\n", section.name());
#endif
if (!section.size())
return true;
char* ptr = (char*)section.address();
if (!ptr) {
kprintf("ELFLoader: failed to allocate section '%s'\n", section.name());
failed = true;
return false;
}
memset(ptr, 0, section.size());
m_sections.set(section.name(), move(ptr));
return true;
});
return !failed;
}
void* ELFLoader::lookup(const ELFImage::Symbol& symbol)
{
if (symbol.section().is_undefined())
return symbol_ptr(symbol.name());
return area_for_section(symbol.section()) + symbol.value();
}
char* ELFLoader::area_for_section(const ELFImage::Section& section)
{
return area_for_section_name(section.name());
}
char* ELFLoader::area_for_section_name(const char* name)
{
if (auto it = m_sections.find(name); it != m_sections.end())
return (*it).value;
ASSERT_NOT_REACHED();
return nullptr;
}
bool ELFLoader::perform_relocations()
{
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Performing relocations\n");
#endif
bool failed = false;
m_image.for_each_section_of_type(SHT_PROGBITS, [this, &failed] (const ELFImage::Section& section) -> bool {
auto& relocations = section.relocations();
if (relocations.is_undefined())
return true;
relocations.for_each_relocation([this, section, &failed] (const ELFImage::Relocation& relocation) {
auto symbol = relocation.symbol();
auto& patch_ptr = *reinterpret_cast<ptrdiff_t*>(area_for_section(section) + relocation.offset());
switch (relocation.type()) {
case R_386_PC32: {
char* target_ptr = (char*)lookup(symbol);
if (!target_ptr) {
kprintf("ELFLoader: unresolved symbol '%s'\n", symbol.name());
failed = true;
return false;
}
ptrdiff_t relativeOffset = (char*)target_ptr - ((char*)&patch_ptr + 4);
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Relocate PC32: offset=%x, symbol=%u(%s) value=%x target=%p, offset=%d\n",
relocation.offset(),
symbol.index(),
symbol.name(),
symbol.value(),
target_ptr,
relativeOffset
);
#endif
patch_ptr = relativeOffset;
break;
}
case R_386_32: {
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Relocate Abs32: symbol=%u(%s), value=%x, section=%s\n",
symbol.index(),
symbol.name(),
symbol.value(),
symbol.section().name()
);
#endif
char* target_ptr = area_for_section(symbol.section()) + symbol.value();
patch_ptr += (ptrdiff_t)target_ptr;
break;
}
default:
ASSERT_NOT_REACHED();
break;
}
return true;
});
return !failed;
});
return !failed;
}
void ELFLoader::export_symbols()
{
m_image.for_each_symbol([&] (const ELFImage::Symbol symbol) {
#ifdef ELFLOADER_DEBUG
kprintf("symbol: %u, type=%u, name=%s, section=%u\n", symbol.index(), symbol.type(), symbol.name(), symbol.sectionIndex());
#endif
if (symbol.type() == STT_FUNC) {
char* ptr;
if (m_image.is_executable())
ptr = (char*)symbol.value();
else if (m_image.is_relocatable())
ptr = area_for_section(symbol.section()) + symbol.value();
else
ASSERT_NOT_REACHED();
add_symbol(symbol.name(), ptr, symbol.size());
}
// FIXME: What about other symbol types?
return true;
});
}
char* ELFLoader::symbol_ptr(const char* name)
{
if (auto it = m_symbols.find(name); it != m_symbols.end()) {
auto& symbol = (*it).value;
#ifdef EXECSPACE_DEBUG
kprintf("[ELFLoader] symbol_ptr(%s) dump:\n", name);
disassemble(symbol.ptr, symbol.size);
#endif
return symbol.ptr;
}
return nullptr;
}
bool ELFLoader::allocate_section(LinearAddress laddr, size_t size, size_t alignment, bool is_readable, bool is_writable)
{
ASSERT(alloc_section_hook);
char namebuf[16];
ksprintf(namebuf, "elf-alloc-%s%s", is_readable ? "r" : "", is_writable ? "w" : "");
return alloc_section_hook(laddr, size, alignment, is_readable, is_writable, namebuf);
}
bool ELFLoader::map_section(LinearAddress laddr, size_t size, size_t alignment, size_t offset_in_image, bool is_readable, bool is_writable)
{
ASSERT(alloc_section_hook);
char namebuf[16];
ksprintf(namebuf, "elf-map-%s%s", is_readable ? "r" : "", is_writable ? "w" : "");
return map_section_hook(laddr, size, alignment, offset_in_image, is_readable, is_writable, namebuf);
}
void ELFLoader::add_symbol(String&& name, char* ptr, unsigned size)
{
m_symbols.set(move(name), { ptr, size });
}
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