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83 lines
2.8 KiB
C++
83 lines
2.8 KiB
C++
#include "elf_load.hpp"
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#include "elf_format.hpp"
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#include <algorithm>
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#include <cstring>
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static const unsigned char elf_header[] = { '\177', 'E', 'L', 'F' };
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template<typename T>
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constexpr static auto ptr_from_offset(void *base, uint32_t offset)
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{
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return reinterpret_cast<T>(reinterpret_cast<uint8_t *>(base) + offset);
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}
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static Elf32_Shdr *find_section(Elf32_Ehdr *ehdr, const char *name);
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namespace elf {
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entry_t load(void *elf_data, void *elf_load_offset)
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{
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auto ehdr = reinterpret_cast<Elf32_Ehdr *>(elf_data);
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if (!std::equal(ehdr->e_ident, ehdr->e_ident + 4, elf_header))
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return nullptr;
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auto phdr = ptr_from_offset<Elf32_Phdr *>(elf_data, ehdr->e_phoff);
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for (Elf32_Half i = 0; i < ehdr->e_phnum; i++) {
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if (phdr->p_type == PT_LOAD) {
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std::memcpy(ptr_from_offset<void *>(elf_load_offset, phdr->p_vaddr),
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ptr_from_offset<void *>(elf_data, phdr->p_offset),
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phdr->p_filesz);
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//break;
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}
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phdr = ptr_from_offset<Elf32_Phdr *>(phdr, ehdr->e_phentsize);
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}
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// Zero .bss section
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if (auto bss_section = find_section(ehdr, ".bss"); bss_section) {
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auto bss = ptr_from_offset<uint32_t *>(elf_load_offset, bss_section->sh_addr);
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std::fill(bss, bss + bss_section->sh_size / sizeof(uint32_t), 0);
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}
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// Fix global offset table (GOT) entries
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if (auto got_section = find_section(ehdr, ".got"); got_section) {
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auto got = ptr_from_offset<void **>(elf_load_offset, got_section->sh_addr);
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for (size_t i = 0; i < got_section->sh_size / sizeof(void *); i++)
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got[i] = ptr_from_offset<void *>(got[i], reinterpret_cast<uint32_t>(elf_load_offset));
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}
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//// Run any initial constructors
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//if (auto init_section = find_section(ehdr, ".init_array"); init_section) {
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// auto init_array = reinterpret_cast<void (**)()>(elf_load_offset + init_section->sh_addr);
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// std::for_each(init_array, init_array + init_section->sh_size / sizeof(void (*)()),
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// [elf_load_offset](auto func) { (func + elf_load_offset)(); });
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//}
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// Find filter code start
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if (auto filter = find_section(ehdr, ".process_data"); filter)
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return ptr_from_offset<entry_t>(elf_load_offset, filter->sh_addr | 1); // OR 1 to enable thumb
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else
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return nullptr;
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}
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} // namespace elf
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Elf32_Shdr *find_section(Elf32_Ehdr *ehdr, const char *name)
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{
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auto shdr = ptr_from_offset<Elf32_Shdr *>(ehdr, ehdr->e_shoff);
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auto shdr_str = ptr_from_offset<Elf32_Shdr *>(ehdr,
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ehdr->e_shoff + ehdr->e_shstrndx * ehdr->e_shentsize);
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for (Elf32_Half i = 0; i < ehdr->e_shnum; i++) {
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char *section = ptr_from_offset<char *>(ehdr, shdr_str->sh_offset) + shdr->sh_name;
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if (!strcmp(section, name))
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return shdr;
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shdr = ptr_from_offset<Elf32_Shdr *>(shdr, ehdr->e_shentsize);
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}
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return 0;
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}
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