Simple elf parser.

elfparse.c

#include <stdint.h>
#include <stdlib.h>
#include <elf.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>

void readElfHeader(Elf64_Ehdr *ehdr);

int main(int argc, char **argv) {
	if (argc != 2) {
		printf("Incorrect number of arguments\n");
		exit(0);
	}

	/* Open the file */
	FILE *fp = fopen(argv[1], "rb");
	if (fp == NULL) {
		perror("fopen");
		exit(-1);
	}

	/* Get the size of the file */
	fseek(fp, 0L, SEEK_END);
	long int file_size = ftell(fp);
	rewind(fp);

	/* Map the entire binary into memory for quick random access */
	uint8_t *addr = mmap(NULL, file_size, PROT_READ, MAP_PRIVATE, fileno(fp), 0);
	if (addr == MAP_FAILED) {
		perror("mmap");
		exit(-1);
	}

	/* Assign ELF Header, program header table, and section header table */
	Elf64_Ehdr *ehdr = (Elf64_Ehdr *)(addr);
	Elf64_Phdr *phdr = (Elf64_Phdr *)(addr + ehdr->e_phoff);
	Elf64_Shdr *shdr = (Elf64_Shdr *)(addr + ehdr->e_shoff);

	/* Make sure it is a valid ELF Binary by checking magic numbers */
	if (ehdr->e_ident[0] != 0x7f ||
	    ehdr->e_ident[1] != 'E' ||
		ehdr->e_ident[2] != 'L' ||
		ehdr->e_ident[3] != 'F') {
			printf("File is not an ELF Binary\n");
			exit(-1);
	}

	/* Make sure it is an executable ELF file */
	if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN) {
		printf("%d\n", ehdr->e_type);
		printf("ELF file is not executable\n");
		exit(-1);
	}

	/* Extract Information from the ELF Header */
	readElfHeader(ehdr);

	/* Get the string table */
	uint8_t *string_table = &addr[shdr[ehdr->e_shstrndx].sh_offset];

	/* Print Section Header Table */
	printf("Section Headers:\n");
	printf("\tName : Offset\n");
	for (int i = 0; i < ehdr->e_shnum; i++) {
		printf("\t%s : 0x%lx\n", &string_table[shdr[i].sh_name], shdr[i].sh_offset);
	}
	printf("\n");

	/* Print Program Header Table */
	printf("Program Headers:\n");
	printf("\tType : Offset : Virtual Address\n");
	for (int i = 0; i < ehdr->e_phnum; i++) {
		printf("\t%d : 0x%lx : 0x%lx\n", phdr[i].p_type, phdr[i].p_offset, phdr[i].p_vaddr);
	}
	printf("\n");
}

/*
 * Extract information from the ELF Header:
 * 		Magic Bytes
 * 		Entry Point Address
 * 		Start of Program Headers (offset)void readSectionHeaders(Elf64_Shdr *shdr, Elf64_Shdr *string_table)
 * 		Start of Section Headers (address)
 * 		Size of ELF Header
 * 		Number of Program Headers
 * 		Number of Section Headers
 */
void readElfHeader(Elf64_Ehdr *ehdr) {
	printf("ELF Header (%d bytes):\n", ehdr->e_ehsize);
	
	/* Print Magic Bytes */
	printf("\tMagic:\t");
	for (int i = 0; i < 16; i++) {
		printf("%02x ", *(((uint8_t *) ehdr) + i));
	}
	printf("\n");

	/* Print Entry Point Address */
	printf("\tEntry Point:\t%lx\n", ehdr->e_entry);

	/* Print Start of Program Headers */
	printf("\tStart of Program Headers:\t%ld (bytes into file)\n",
			ehdr->e_phoff);

	/* Print Start of Section Headers */
	printf("\tStart of Section Headers:\t%ld (bytes into file)\n",
			ehdr->e_shoff);

	/* Print Size of Program Headers */
	printf("\tSize of Program Headers:\t%d (bytes)\n", ehdr->e_phentsize);

	/* Print Number of Program Headers */
	printf("\tNumber of Program Headers:\t%d\n", ehdr->e_phnum);

	/* Print Size of Section Headers */
	printf("\tSize of Section Headers:\t%d (bytes)\n", ehdr->e_shentsize);

	/* Print Number of Section Headers */
	printf("\tNumber of Section Headers:\t%d\n", ehdr->e_shnum);

	printf("\n");
}