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/*
* Copyright (c) 2021, Gunnar Beutner <gbeutner@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <LibC/elf.h>
#include <LibELF/Relocation.h>
namespace ELF {
bool perform_relative_relocations(FlatPtr base_address)
{
ElfW(Ehdr)* header = (ElfW(Ehdr)*)(base_address);
ElfW(Phdr)* pheader = (ElfW(Phdr)*)(base_address + header->e_phoff);
FlatPtr dynamic_section_addr = 0;
for (size_t i = 0; i < (size_t)header->e_phnum; ++i, ++pheader) {
if (pheader->p_type != PT_DYNAMIC)
continue;
dynamic_section_addr = pheader->p_vaddr + base_address;
}
if (!dynamic_section_addr)
return false;
FlatPtr relocation_section_addr = 0;
size_t relocation_table_size = 0;
size_t relocation_count = 0;
bool use_addend = false;
auto* dyns = reinterpret_cast<const ElfW(Dyn)*>(dynamic_section_addr);
for (unsigned i = 0;; ++i) {
auto& dyn = dyns[i];
if (dyn.d_tag == DT_NULL)
break;
if (dyn.d_tag == DT_RELA)
use_addend = true;
if (dyn.d_tag == DT_REL || dyn.d_tag == DT_RELA)
relocation_section_addr = base_address + dyn.d_un.d_ptr;
else if (dyn.d_tag == DT_RELCOUNT || dyn.d_tag == DT_RELACOUNT)
relocation_count = dyn.d_un.d_val;
else if (dyn.d_tag == DT_RELSZ || dyn.d_tag == DT_RELASZ)
relocation_table_size = dyn.d_un.d_val;
}
if (!relocation_section_addr || !relocation_table_size || !relocation_count)
return false;
auto relocation_entry_size = relocation_table_size / relocation_count;
for (unsigned i = 0; i < relocation_count; ++i) {
size_t offset_in_section = i * relocation_entry_size;
auto* relocation = (ElfW(Rela)*)(relocation_section_addr + offset_in_section);
#if ARCH(I386)
VERIFY(ELF32_R_TYPE(relocation->r_info) == R_386_RELATIVE);
#else
VERIFY(ELF64_R_TYPE(relocation->r_info) == R_X86_64_RELATIVE);
#endif
auto* patch_address = (FlatPtr*)(base_address + relocation->r_offset);
FlatPtr relocated_address;
if (use_addend) {
relocated_address = base_address + relocation->r_addend;
} else {
__builtin_memcpy(&relocated_address, patch_address, sizeof(relocated_address));
relocated_address += base_address;
}
__builtin_memcpy(patch_address, &relocated_address, sizeof(relocated_address));
}
return true;
}
}
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