stuff
This commit is contained in:
p-w-rs
307
TTOS/src/elf.c
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307
TTOS/src/elf.c
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#include <stdint.h>
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#include <string.h>
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#include <stdio.h>
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#include "fs/fs.h"
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#include "syscall.h"
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#include "elf.h"
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#include "process.h"
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#include "memory.h"
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static int validate_magic(uint8_t e_ident[EI_NIDENT]) {
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// ELF Magic must match
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if(e_ident[0] != ELFMAG0 || e_ident[1] != ELFMAG1 || e_ident[2] != ELFMAG2 || e_ident[3] != ELFMAG3) {
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return -1;
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}
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// Currently, only support 64 bit executables
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if(e_ident[4] != ELFCLASS64) {
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return -1;
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}
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// Currently, only support LSB byte order executables
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if(e_ident[5] != ELFDATA2LSB) {
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return -1;
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}
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// Currently, only support ELF current version
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if(e_ident[6] != EV_CURRENT) {
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return -1;
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}
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return 0;
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}
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static errorCode_t get_file_data(const char* path, elf_file* file) {
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int rc;
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// Open the file
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int fd = 0;
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rc = fs_open(path, O_RDONLY, &fd);
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if(IS_ERROR(rc)) {
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return rc;
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}
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// Seek to the beginning and then the end
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// to get the file size
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fs_seek(fd, 0, SEEK_SET, 0);
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rc = fs_seek(fd, 0, SEEK_END, &file->size);
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if(IS_ERROR(file->size) || file->size == 0) {
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return EBADEXEC;
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}
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rc = get_kernel_memory(file->size, &file->contents);
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if(IS_ERROR(rc)) {
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return rc;
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}
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// Seek to the beginning and read the file data
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fs_seek(fd, 0, SEEK_SET, 0);
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int bytes_read = 0;
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rc = fs_read(fd, file->contents, file->size, &bytes_read);
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// Check error if error use error code if one was returned
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if(IS_ERROR(rc)) {
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free_kernel_memory(file->contents, file->size);
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fs_close(fd);
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return rc;
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}
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// Check error ELIBBAD if data read != size
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if(bytes_read != file->size) {
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free_kernel_memory(file->contents, file->size);
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fs_close(fd);
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return EBADEXEC;
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}
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// Close the file and return
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fs_close(fd);
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return 0;
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}
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static Elf64_Phdr* get_program_header(elf_file* file, int index) {
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return (Elf64_Phdr*)((char*)file->phdr + index * file->ehdr->e_phentsize);
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}
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static Elf64_Shdr* get_section_header(elf_file* file, int index) {
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return (Elf64_Shdr*)((char*)file->shdr + index * file->ehdr->e_shentsize);
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}
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static void* find_external_symbol(elf_file* file, Elf64_Shdr *symtbl_shdr, Elf64_Word st_name) {
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if(symtbl_shdr->sh_link == 0) {
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return 0;
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}
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Elf64_Shdr* strtbl_hdr = get_section_header(file, symtbl_shdr->sh_link);
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char* strtbl = (char*)((uint8_t*)file->contents + strtbl_hdr->sh_offset);
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char* symbol_name = &(strtbl[st_name]);
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if(strncmp(symbol_name, "system_call", 7) == 0) {
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return system_call;
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}
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return 0;
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}
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static errorCode_t relocate_symbols(elf_file* file, void* tgt_addr) {
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for(int i = 0; i < file->ehdr->e_shnum; i++) {
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Elf64_Shdr* shdr = get_section_header(file, i);
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if(shdr->sh_type == SHT_REL || shdr->sh_type == SHT_RELA) {
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// Retrieve the sections headers for the relocation section, linked symbol table, and target section
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Elf64_Shdr* rel_shdr = shdr;
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Elf64_Shdr *symtbl_shdr = get_section_header(file, rel_shdr->sh_link);
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Elf64_Shdr *tgt_shdr = get_section_header(file, rel_shdr->sh_info);
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// Retrieve the linked symbol table
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Elf64_Sym* symtbl = (Elf64_Sym*)((uint8_t*)file->contents + symtbl_shdr->sh_offset);
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// Loop through each relocation entry and update the target
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int entry_count = rel_shdr->sh_size / rel_shdr->sh_entsize;
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for (int j = 0; j < entry_count; j++) {
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Elf64_Rela* relhdr = (Elf64_Rela*)((uint8_t*)file->contents + rel_shdr->sh_offset + j*rel_shdr->sh_entsize);
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Elf64_Xword symbol = ELF64_R_SYM(relhdr->r_info);
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Elf64_Xword type = ELF64_R_TYPE(relhdr->r_info);
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// Symbol address
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// For relocatable files - start of the exec + offset to the section containing the symbol + offset to the symbol in the section (aka symbol value)
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// For all other files - start of the exec + symbol value (aka virtual address)
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// For undefined symbols - search for the symbol externally
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void* symbol_address = 0;
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if(file->ehdr->e_type == ET_REL) {
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symbol_address = (void*)((uint8_t*)tgt_addr + file->shdr[symtbl[symbol].st_shndx].sh_offset + symtbl[symbol].st_value);
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} else if(symtbl[symbol].st_shndx == STN_UNDEF) {
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symbol_address = find_external_symbol(file, symtbl_shdr, symtbl[symbol].st_name);
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} else {
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symbol_address = (void*)((uint8_t*)tgt_addr + symtbl[symbol].st_value);
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}
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if(symbol_address == 0) {
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return -1;
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}
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// Location in section to patch
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// For relocatable files - start of exec + offset to patch section + offset in the section
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// For all other files - start of the exec + relocation offset value (aka virtual address)
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void* patch_location = file->ehdr->e_type == ET_REL ?
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(void*)((uint8_t*)tgt_addr + tgt_shdr->sh_offset + relhdr->r_offset) :
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(void*)((uint8_t*)tgt_addr + relhdr->r_offset);
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// retrieve the addend, only applies to RELA entries
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Elf64_Sxword addend = file->shdr[i].sh_type == SHT_RELA ? relhdr->r_addend : 0;
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// https://refspecs.linuxbase.org/elf/x86_64-abi-0.98.pdf page 69
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switch(type) {
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case R_X86_64_PC8:
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*(uint8_t*)patch_location = (uint8_t*)symbol_address + addend - (uint8_t*)patch_location;
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break;
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case R_X86_64_PC16:
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*(uint16_t*)patch_location = (uint8_t*)symbol_address + addend - (uint8_t*)patch_location;
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case R_X86_64_PC32:
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case R_X86_64_PLT32:
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*(uint32_t*)patch_location = (uint8_t*)symbol_address + addend - (uint8_t*)patch_location;
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break;
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case R_X86_64_PC64:
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*(uint64_t*)patch_location = (uint8_t*)symbol_address + addend - (uint8_t*)patch_location;
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break;
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case R_X86_64_GLOB_DAT:
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case R_X86_64_JUMP_SLOT:
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*(uint64_t*)patch_location = (uint64_t)symbol_address;
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break;
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}
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// printf("%lX %lX %016lX %016lX\n", symbol, type, (uint64_t)symbol_address, (uint64_t)patch_location);
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}
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}
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}
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return SUCCESS;
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}
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errorCode_t load_elf(const char* path, elf_file* file) {
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if(file == 0 || path == 0) {
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return EBADPARM;
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}
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// Initialize the file and retrieve the file data
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memset(file, 0x00, sizeof(elf_file));
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int rc = get_file_data(path, file);
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if(IS_ERROR(rc)) {
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return rc;
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}
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// Validate the file magic value
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if(validate_magic(file->contents) != 0) {
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free_elf(file);
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return EBADEXEC;
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}
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file->ehdr = (Elf64_Ehdr*)file->contents;
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/* Only support dynamic linked files */
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if(file->ehdr->e_type != ET_DYN) {
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free_elf(file);
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return EBADEXEC;
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}
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if(file->ehdr->e_phoff == 0) {
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free_elf(file);
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return EBADEXEC;
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}
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file->phdr = (Elf64_Phdr*)((uint8_t*)file->contents + file->ehdr->e_phoff);
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if(file->ehdr->e_shoff == 0) {;
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free_elf(file);
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return EBADEXEC;
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}
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file->shdr = (Elf64_Shdr*)((uint8_t*)file->contents + file->ehdr->e_shoff);
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return SUCCESS;
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}
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errorCode_t get_elf_proc_size(elf_file* file, uint64_t* size) {
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if(file == 0 || size == 0) {
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return EBADPARM;
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}
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// Determine the size to allocate for the process
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// Determined by the highest address of any memory segment in the program header
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Elf64_Phdr* highest_header = 0;
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for(int i = 0; i < file->ehdr->e_phnum; i++) {
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Elf64_Phdr *phdr = get_program_header(file, i);
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if (phdr->p_type == PT_LOAD) {
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if (highest_header == 0 || highest_header->p_vaddr < phdr->p_vaddr) {
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highest_header = phdr;
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}
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}
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}
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*size = (uint64_t)highest_header->p_vaddr + (uint64_t)highest_header->p_memsz;
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return SUCCESS;
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}
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errorCode_t populate_elf_proc(elf_file* file, void* tgt_addr) {
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if(file == 0 || tgt_addr == 0) {
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return EBADPARM;
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}
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// Copy program sections into the process
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for(int i = 0; i < file->ehdr->e_shnum; i++) {
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Elf64_Shdr* shdr = get_section_header(file, i);
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if(shdr && (shdr->sh_flags & SHF_ALLOC) && shdr->sh_addr > 0) {
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memcpy(((uint8_t*)tgt_addr) + shdr->sh_addr, ((uint8_t*)file->contents) + shdr->sh_offset, shdr->sh_size);
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}
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}
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// Relocate symbols
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return relocate_symbols(file, tgt_addr);
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}
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errorCode_t find_symbol(elf_file* file, const char* name, uint64_t* offset) {
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if(offset == 0) {
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return EBADPARM;
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}
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// Search for a symbol
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// Iterate through each section
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for(int i = 0; i < file->ehdr->e_shnum; i++) {
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// Find a section that represents a symbol table
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Elf64_Shdr* shdr = get_section_header(file, i);
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if(shdr->sh_type == SHT_SYMTAB) {
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// Retrieve the corresponding string table
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Elf64_Shdr* strtbl_hdr = get_section_header(file, shdr->sh_link);
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char* strtbl = (char*)((uint8_t*)file->contents + strtbl_hdr->sh_offset);
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// Iterate through each entry searching for the symbol string
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int entry_count = shdr->sh_size / shdr->sh_entsize;
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for(int j = 0; j < entry_count; j++) {
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Elf64_Sym* symtbl = (Elf64_Sym*)((uint8_t*)file->contents + shdr->sh_offset + j*shdr->sh_entsize);
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char* symbol_name = &(strtbl[symtbl->st_name]);
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// Check symbol name and return offset
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// For relocatable files - offset to symbol table + offset to the symbol (aka symbol value)
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// For all other files - symbol value (aka virtual address)
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if(strcmp(symbol_name, name) == 0) {
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if(file->ehdr->e_type == ET_REL) {
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*offset = file->shdr[symtbl->st_shndx].sh_offset + symtbl->st_value;
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} else {
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*offset = symtbl->st_value;
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}
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return SUCCESS;
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}
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}
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}
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}
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return ENOTFOUND;
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}
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errorCode_t free_elf(elf_file* file) {
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free_kernel_memory(file->contents, file->size);
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memset(file, 0x00, sizeof(elf_file));
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return SUCCESS;
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}
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