Read binary data from a file into a C struct using mmap(2)

mmap_interp.c

/*
 * Load raw binary data from a mmap(2)'ed file
 * Mind your endianness and alignment.
 *
 * Sun, 12 Jan 2020 12:00:00 +0000
 * By Gydo194
 *
 * This code is in the public domain, you may use and redistribute this
 * file as you wish, however I shall not be responsible for any damage caused
 * by you doing so.
 */

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

#define COLOR_RED	"\e[31m"
#define COLOR_GREEN	"\e[32m"
#define COLOR_RESET	"\e[0m"

typedef unsigned char u8_t;
typedef unsigned short u16_t;

struct mtef
{
	u8_t value1;
	u8_t value2;
};

/* file as unsigned char for now */
unsigned char *file;

int size, status, fd;
struct stat s;

void mmap_file(const char * const filename)
{
	/* open file */
	fd = open (filename, O_RDONLY);

	/* Get the size of the file. */
	status = fstat (fd, & s);
	size = s.st_size;

	file = (char *) mmap (0, size, PROT_READ, MAP_PRIVATE, fd, 0);
}

void interpret_memory_region(const void * const address)
{
	const struct mtef * mtef_region;
	u8_t parsed_value1, parsed_value2;

	/* zero just to be sure */
	parsed_value1 = 0x00;
	parsed_value2 = 0x00;

	/* cast raw memory region to struct */
	mtef_region = (const struct mtef *) address;
	printf(COLOR_GREEN "Loaded address '0x%X' as MTEF struct" COLOR_RESET "\n", mtef_region);

	/* copy values from mapped address onto the stack */
	puts("Loading values...");
	parsed_value1 = mtef_region->value1;
	parsed_value2 = mtef_region->value2;
	puts(COLOR_GREEN "Success!" COLOR_RESET);

	/* if all goes well.. */
	printf(COLOR_GREEN "VALUE 1: '%d'\nVALUE 2: '%d'" COLOR_RESET "\n", parsed_value1, parsed_value2);
}

int main(int argc, char const *argv[])
{

	if(argc < 2)
	{
		/* i do want a file path from you */
		printf(COLOR_RED "Usage: %s <file>" COLOR_RESET "\n", argv[0]);
		return 1;
	}

	printf("Loading file '%s' ...\n", argv[1]);
	mmap_file(argv[1]);
	puts(COLOR_GREEN "Success!" COLOR_RESET);
	interpret_memory_region(file);

	return 0;
}

You are not unmapping the memory and closing the file. That is a big uff

You are not unmapping the memory and closing the file. That is a big uff

Left as an excersise to the reader.

This was just a proof of concept to show how this works to my friend. Error handling and proper cleanup has been neglected a bit. Maybe i should have stated that sonewhere.