#include <sys/param.h>
#include <err.h>
#include <fcntl.h>
#include <libelf.h>
#include <stdio.h>
#include <stdlib.h>
#include <sysexits.h>
#include <unistd.h>

uint32_t hash_words[] = {
	0x01234567,
	0x89abcdef,
	0xdeadc0de
};

char string_table[] = {
	/* Offset 0 */	'\0',
	/* Offset 1 */	'.', 'f', 'o', 'o', '\0',
	/* Offset 6 */	'.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', '\0'
};

int
main(int argc, char **argv)
{
	int fd;
	size_t off_shstrtab, off_foo;
	Elf *e;
	Elf_Scn *scn;
	Elf_Data *data;
	Elf32_Ehdr *ehdr;
	Elf32_Phdr *phdr;
	Elf32_Shdr *shdr;

	if (argc != 2)
		errx(EX_USAGE, "usage: %s file-name", getprogname());

	if (elf_version(EV_CURRENT) == EV_NONE)
		errx(EX_SOFTWARE, "ELF library initialization failed: %s",
		    elf_errmsg(-1));

	if ((fd = open(argv[1], O_WRONLY|O_CREAT, 0777)) < 0)
		err(EX_OSERR, "open \"%s\" failed", argv[1]);

	if ((e = elf_begin(fd, ELF_C_WRITE, NULL)) == NULL)
		errx(EX_SOFTWARE, "elf_begin() failed: %s.",
		    elf_errmsg(-1));

	/* App control LAYOUT */
	elf_flagelf(e, ELF_C_SET, ELF_F_LAYOUT);

	if ((ehdr = elf32_newehdr(e)) == NULL)
		errx(EX_SOFTWARE, "elf32_newehdr() failed: %s.",
		    elf_errmsg(-1));

	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
	ehdr->e_machine = EM_386;
	ehdr->e_type = ET_EXEC;

	if ((phdr = elf32_newphdr(e, 1)) == NULL)
		errx(EX_SOFTWARE, "elf32_newphdr() failed: %s.",
		    elf_errmsg(-1));

	/* Calculate offsets */
	ehdr->e_phoff = elf32_fsize(ELF_T_EHDR, 1, EV_CURRENT);
	off_foo = ehdr->e_phoff + elf32_fsize(ELF_T_PHDR, 1, EV_CURRENT);
	off_shstrtab = off_foo + sizeof(hash_words);
	ehdr->e_shoff = roundup(off_shstrtab + sizeof(string_table), 4);
	printf("phoff = %d\n", ehdr->e_phoff);
	printf("off_foo = %d\n", off_foo);
	printf("off_shstrtab = %d\n", off_shstrtab);
	printf("shoff = %d\n", ehdr->e_shoff);

	/* Create .shstrtab fisrt */
	if ((scn = elf_newscn(e)) == NULL)
		errx(EX_SOFTWARE, "elf_newscn() failed: %s.",
		    elf_errmsg(-1));

	if ((data = elf_newdata(scn)) == NULL)
		errx(EX_SOFTWARE, "elf_newdata() failed: %s.",
		    elf_errmsg(-1));

	data->d_align = 1;
	data->d_buf = string_table;
	data->d_off = 0LL;
	data->d_size = sizeof(string_table);
	data->d_type = ELF_T_BYTE;
	data->d_version = EV_CURRENT;

	if ((shdr = elf32_getshdr(scn)) == NULL)
		errx(EX_SOFTWARE, "elf32_getshdr() failed: %s.",
		    elf_errmsg(-1));

	shdr->sh_name = 6;
	shdr->sh_offset = off_shstrtab;
	shdr->sh_size = sizeof(string_table);
	shdr->sh_addralign = data->d_align;
	shdr->sh_type = SHT_STRTAB;
	shdr->sh_flags = SHF_STRINGS | SHF_ALLOC;
	shdr->sh_entsize = 0;

	elf_setshstrndx(e, elf_ndxscn(scn));

	/* Create .foo */
	if ((scn = elf_newscn(e)) == NULL)
		errx(EX_SOFTWARE, "elf_newscn() failed: %s.",
		    elf_errmsg(-1));

	if ((data = elf_newdata(scn)) == NULL)
		errx(EX_SOFTWARE, "elf_newdata() failed: %s.",
		    elf_errmsg(-1));

	data->d_align = 4;
	data->d_off  = 0LL;
	data->d_buf  = hash_words;
	data->d_type = ELF_T_WORD;
	data->d_size = sizeof(hash_words);
	data->d_version = EV_CURRENT;

	if ((shdr = elf32_getshdr(scn)) == NULL)
		errx(EX_SOFTWARE, "elf32_getshdr() failed: %s.",
		    elf_errmsg(-1));

	shdr->sh_name = 1;
	shdr->sh_offset = off_foo;
	shdr->sh_size = sizeof(hash_words);
	shdr->sh_addralign = data->d_align;
	shdr->sh_type = SHT_HASH;
	shdr->sh_flags = SHF_ALLOC;
	shdr->sh_entsize = 0;

	if (elf_update(e, ELF_C_NULL) < 0)
		errx(EX_SOFTWARE, "elf_update(NULL) failed: %s.",
		    elf_errmsg(-1));

	phdr->p_type = PT_PHDR;
	phdr->p_offset = ehdr->e_phoff;
	phdr->p_filesz = elf32_fsize(ELF_T_PHDR, 1, EV_CURRENT);

	(void) elf_flagphdr(e, ELF_C_SET, ELF_F_DIRTY);

	if (elf_update(e, ELF_C_WRITE) < 0)
		errx(EX_SOFTWARE, "elf_update() failed: %s.",
		    elf_errmsg(-1));

	(void) elf_end(e);
	(void) close(fd);

	exit(EX_OK);
}