Convert raw AVR binary firmware to ELF format loadable to QEMU

main.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <errno.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/mman.h>

#include <libelf.h>


int main (int argc, char** argv) {
	if (argc < 2) {
		fprintf(stderr, "Usage: %s input.bin output.elf\n", argv[0]);

		return 1;
	}

	char* binary = argv[1];
	char* filename = argv[2];

	struct stat s;
	int fd_input = open(binary, O_RDONLY);
	if (fd_input < 0) {
		fprintf(stderr, "Cannot open file %s: %s\n", binary, strerror(errno));

		return 1;
	}

	fstat(fd_input, &s);
	size_t b_size = s.st_size;

	unsigned char *b_ptr = (unsigned char*) mmap(0, s.st_size, PROT_READ, MAP_PRIVATE, fd_input, 0);
	if (b_ptr == NULL) {
		fprintf(stderr, "Cannot read file %s: %s\n", binary, strerror(errno));

		return 1;
	}

	int fd = open(filename, O_WRONLY | O_CREAT, 0755);
	if (fd < 0) {
		fprintf(stderr, "Cannot open file %s: %s\n", filename, strerror(errno));

		return 1;
	}

	elf_version(EV_CURRENT);
	Elf *elf = elf_begin(fd, ELF_C_WRITE, NULL);
	if (elf == NULL) {
		fprintf(stderr, "Cannot create ELF: %s\n", elf_errmsg(elf_errno()));

		close(fd);

		return 1;
	}

	Elf32_Ehdr *ehdr = elf32_newehdr(elf);
	if (ehdr == NULL) {
		fprintf(stderr, "Cannot create EHDR: %s\n", elf_errmsg(elf_errno()));

		elf_end(elf);

		return 1;
	}

	ehdr->e_type = ET_EXEC;
	ehdr->e_machine = EM_AVR;
	ehdr->e_version = EV_CURRENT;
	ehdr->e_flags = 0x4;

	Elf_Scn *text_scn = elf_newscn(elf);
	if (text_scn == NULL) {
		fprintf(stderr, "Cannot create .text section: %s\n", elf_errmsg(elf_errno()));

		elf_end(elf);

		return 1;
	}

	Elf32_Shdr *text = elf32_getshdr(text_scn);
	if (text == NULL) {
		fprintf(stderr, "Cannot get .text section: %s\n", elf_errmsg(elf_errno()));

		elf_end(elf);

		return 1;
	}

	Elf_Data *text_data = elf_newdata(text_scn);
	if (text_data == NULL) {
		fprintf(stderr, "Cannot create data for .text section: %s\n", elf_errmsg(elf_errno()));

		elf_end(elf);

		return 1;
	}

	text_data->d_buf = b_ptr;
	text_data->d_type = ELF_T_BYTE;
	text_data->d_size = b_size;
	text_data->d_align = 1;
	text_data->d_version = EV_CURRENT;
	
	text->sh_name = 1;
	text->sh_type = SHT_PROGBITS;
	text->sh_flags = SHF_ALLOC | SHF_EXECINSTR;

	Elf_Scn *shstrtab_scn = elf_newscn(elf);
	if (shstrtab_scn == NULL) {
		fprintf(stderr, "Cannot create .shstrtab section: %s\n", elf_errmsg(elf_errno()));

		elf_end(elf);

		return 1;
	}

	Elf_Data *strtab_data = elf_newdata(shstrtab_scn);
	if (strtab_data == NULL) {
		fprintf(stderr, "Cannot create data for .shstrtab section: %s\n", elf_errmsg(elf_errno()));

		elf_end(elf);

		return 1;
	}

	char strtab_buf[] = "\0.text\0.shstrtab\0";

	strtab_data->d_buf = strtab_buf;
	strtab_data->d_type = ELF_T_BYTE;
	strtab_data->d_size = sizeof(strtab_buf) / sizeof(strtab_buf[0]);
	strtab_data->d_align = 1;
	strtab_data->d_version = EV_CURRENT;

	Elf32_Shdr *shstrtab = elf32_getshdr(shstrtab_scn);
	if (shstrtab == NULL) {
		fprintf(stderr, "Cannot get .shstrtab section: %s\n", elf_errmsg(elf_errno()));

		elf_end(elf);

		return 1;
	}

	shstrtab->sh_name = 7;
	shstrtab->sh_type = SHT_STRTAB;

	ehdr->e_shstrndx = elf_ndxscn(shstrtab_scn);

	Elf32_Phdr *phdr = elf32_newphdr(elf, 1);
	if (phdr == NULL) {
		fprintf(stderr, "Cannot create PHDR: %s\n", elf_errmsg(elf_errno()));

		elf_end(elf);

		return 1;
	}

	phdr->p_type = PT_LOAD;
	phdr->p_vaddr = 0;
	phdr->p_paddr = 0;
	phdr->p_flags = PF_R | PF_X;

	if (elf_update(elf, ELF_C_NULL) < 0) {
		fprintf(stderr, "Cannot write ELF: %s\n", elf_errmsg(elf_errno()));

		elf_end(elf);

		return 1;
	}

	phdr->p_offset = text->sh_offset;
	phdr->p_filesz = text->sh_size;
	phdr->p_memsz = text->sh_size;

	if (elf_update(elf, ELF_C_WRITE) < 0) {
		fprintf(stderr, "Cannot write ELF to disk: %s\n", elf_errmsg(elf_errno()));

		elf_end(elf);

		return 1;
	}

	elf_end(elf);

	return 0;
}