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#include "elf_load.hpp"
#include "elf_format.hpp"
#include <algorithm>
#include <cstring>
static const unsigned char elf_header[] = { '\177', 'E', 'L', 'F' };
template<typename T>
constexpr static auto ptr_from_offset(void *base, uint32_t offset)
{
return reinterpret_cast<T>(reinterpret_cast<uint8_t *>(base) + offset);
}
static Elf32_Shdr *find_section(Elf32_Ehdr *ehdr, const char *name);
namespace elf {
entry_t load(void *elf_data, void *elf_load_offset)
{
auto ehdr = reinterpret_cast<Elf32_Ehdr *>(elf_data);
if (!std::equal(ehdr->e_ident, ehdr->e_ident + 4, elf_header))
return nullptr;
auto phdr = ptr_from_offset<Elf32_Phdr *>(elf_data, ehdr->e_phoff);
for (Elf32_Half i = 0; i < ehdr->e_phnum; i++) {
if (phdr->p_type == PT_LOAD) {
std::memcpy(ptr_from_offset<void *>(elf_load_offset, phdr->p_vaddr),
ptr_from_offset<void *>(elf_data, phdr->p_offset),
phdr->p_filesz);
//break;
}
phdr = ptr_from_offset<Elf32_Phdr *>(phdr, ehdr->e_phentsize);
}
// Zero .bss section
if (auto bss_section = find_section(ehdr, ".bss"); bss_section) {
auto bss = ptr_from_offset<uint32_t *>(elf_load_offset, bss_section->sh_addr);
std::fill(bss, bss + bss_section->sh_size / sizeof(uint32_t), 0);
}
// Fix global offset table (GOT) entries
if (auto got_section = find_section(ehdr, ".got"); got_section) {
auto got = ptr_from_offset<void **>(elf_load_offset, got_section->sh_addr);
for (size_t i = 0; i < got_section->sh_size / sizeof(void *); i++)
got[i] = ptr_from_offset<void *>(got[i], reinterpret_cast<uint32_t>(elf_load_offset));
}
//// Run any initial constructors
//if (auto init_section = find_section(ehdr, ".init_array"); init_section) {
// auto init_array = reinterpret_cast<void (**)()>(elf_load_offset + init_section->sh_addr);
// std::for_each(init_array, init_array + init_section->sh_size / sizeof(void (*)()),
// [elf_load_offset](auto func) { (func + elf_load_offset)(); });
//}
return ptr_from_offset<entry_t>(elf_load_offset, ehdr->e_entry);
}
} // namespace elf
Elf32_Shdr *find_section(Elf32_Ehdr *ehdr, const char *name)
{
auto shdr = ptr_from_offset<Elf32_Shdr *>(ehdr, ehdr->e_shoff);
auto shdr_str = ptr_from_offset<Elf32_Shdr *>(ehdr,
ehdr->e_shoff + ehdr->e_shstrndx * ehdr->e_shentsize);
for (Elf32_Half i = 0; i < ehdr->e_shnum; i++) {
char *section = ptr_from_offset<char *>(ehdr, shdr_str->sh_offset) + shdr->sh_name;
if (!strcmp(section, name))
return shdr;
shdr = ptr_from_offset<Elf32_Shdr *>(shdr, ehdr->e_shentsize);
}
return 0;
}
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