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/**
* @file elf.c
* Functionality to execute ELF files
*
* Copyright (C) 2018 Clyne Sullivan
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#include "elf.h"
#include "vfs.h"
#include "heap.h"
#include <string.h>
/**
* Finds the section with the given name in the ELF data, e.g. ".bss".
* @param ehdr ELF file header
* @param name Name of the section
* @return Section header of the section, NULL if not found
*/
Elf32_Shdr *elf_find_section(Elf32_Ehdr *ehdr, const char *name)
{
Elf32_Shdr *shdr = (Elf32_Shdr *)((char *)ehdr + ehdr->e_shoff);
Elf32_Shdr *shdr_str = (Elf32_Shdr *)((char *)ehdr + ehdr->e_shoff +
ehdr->e_shstrndx * ehdr->e_shentsize);
for (Elf32_Half i = 0; i < ehdr->e_shnum; i++) {
char *section = ((char *)ehdr + shdr_str->sh_offset) +
shdr->sh_name;
if (!strcmp(section, name))
return shdr;
shdr = (Elf32_Shdr *)((char *)shdr + ehdr->e_shentsize);
}
return 0;
}
uint32_t elf_execve(const char *file, char * const argv[], char * const envp[])
{
(void)argv;
(void)envp;
// Open the given file
int fd = vfs_open(file, VFS_FILE_READ);
if (fd == -1)
return -1;
// Get file size
vfs_seek(fd, 0, SEEK_END);
unsigned int fileLength = vfs_tell(fd);
vfs_seek(fd, 0, SEEK_SET);
// Read entire file
char *elfData = malloc(fileLength);
if (vfs_read(fd, fileLength, (uint8_t *)elfData) != fileLength) {
vfs_close(fd);
free(elfData);
return -1;
}
// ELF signature check
if (elfData[0] != '\177' || elfData[1] != 'E' || elfData[2] != 'L' ||
elfData[3] != 'F') {
vfs_close(fd);
free(elfData);
return -1;
}
uint32_t ELF_OFFSET = 0;
// Load program headers
Elf32_Ehdr *ehdr = (Elf32_Ehdr *)elfData;
Elf32_Phdr *phdr = (Elf32_Phdr *)(elfData + ehdr->e_phoff);
// Search for the loadable program header
for (Elf32_Half i = 0; i < ehdr->e_phnum; i++) {
if (phdr->p_type == PT_LOAD) {
// There should only be one PT_LOAD section...
if (ELF_OFFSET != 0)
while (1);
ELF_OFFSET = (uint32_t)malloc(phdr->p_memsz + 8) & ~7;
// Copy the program data into RAM for execution
uint8_t *src = (uint8_t *)elfData + phdr->p_offset;
uint8_t *dst = (uint8_t *)(ELF_OFFSET + phdr->p_vaddr);
for (uint32_t j = 0; j < phdr->p_filesz; j++)
dst[j] = src[j];
}
phdr = (Elf32_Phdr *)((char *)phdr + ehdr->e_phentsize);
}
// Zero the .bss section
Elf32_Shdr *bssSection = elf_find_section(ehdr, ".bss");
if (bssSection != 0) {
uint32_t *bssArray = (Elf32_Addr *)(ELF_OFFSET + bssSection->sh_addr);
Elf32_Word bssSize = bssSection->sh_size / sizeof(void *);
for (Elf32_Word i = 0; i < bssSize; i++)
bssArray[i] = 0;
}
// Fix GOT entries if they exist
Elf32_Shdr *gotSection = elf_find_section(ehdr, ".got");
if (gotSection != 0) {
Elf32_Addr *gotArray = (Elf32_Addr *)(ELF_OFFSET + gotSection->sh_addr);
Elf32_Word gotSize = gotSection->sh_size / sizeof(void *);
for (Elf32_Word i = 0; i < gotSize; i++)
gotArray[i] += ELF_OFFSET;
}
// Run any initial constructors
Elf32_Shdr *initArraySection = elf_find_section(ehdr, ".init_array");
if (initArraySection != 0) {
Elf32_Addr *initArray = (Elf32_Addr *)(ELF_OFFSET +
initArraySection->sh_addr);
Elf32_Word initArraySize = initArraySection->sh_size / sizeof(void *);
for (Elf32_Word i = 0; i < initArraySize; i++) {
initArray[i] += ELF_OFFSET;
((void (*)(void))(initArray[i]))();
}
}
vfs_close(fd);
free(elfData);
// Return entry point
return (ELF_OFFSET + ehdr->e_entry);
}
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