Example for parsing a mach-o using the ITERCMDS macro (best thing ever!)

printsegs.c

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <stdint.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <mach-o/loader.h>

/* Get the next load command from the current one */
#define NEXTCMD(cmd) (struct load_command*)((char*)(cmd) + (cmd)->cmdsize)

/* Iterate through all load commands */
#define ITERCMDS(i, cmd, cmds, ncmds) for(i = 0, cmd = (cmds); i < (ncmds); i++, cmd = NEXTCMD(cmd))

/* Prints the names and address ranges of all segments in the mach-o */
void print_segment_names(struct mach_header* mh, size_t filesize) {
	bool is64bit = false;
	
	uint32_t i, ncmds;
	struct load_command* cmd, *cmds;
	
	/* Parse mach_header to get the first load command and the number of commands */
	if(mh->magic != MH_MAGIC) {
		if(mh->magic == MH_MAGIC_64) {
			is64bit = true;
			struct mach_header_64* mh64 = (struct mach_header_64*)mh;
			cmds = (struct load_command*)&mh64[1];
			ncmds = mh64->ncmds;
		}
		else {
			fprintf(stderr, "Invalid magic number: %08X\n", mh->magic);
			return;
		}
	}
	else {
		cmds = (struct load_command*)&mh[1];
		ncmds = mh->ncmds;
	}
	
	/* Iterate through the mach-o's load commands */
	ITERCMDS(i, cmd, cmds, ncmds) {
		/* Make sure we don't loop infinitely */
		if(cmd->cmdsize == 0) {
			break;
		}
		
		/* Make sure the load command is completely contained in the file */
		if((uintptr_t)cmd + cmd->cmdsize - (uintptr_t)mh > filesize) {
			break;
		}
		
		/* Process the load command */
		switch(cmd->cmd) {
			case LC_SEGMENT: {
				struct segment_command* seg = (struct segment_command*)cmd;
				printf("%16s: %08x - %08x\n", seg->segname, seg->vmaddr, seg->vmsize);
				break;
			}
			
			case LC_SEGMENT_64: {
				struct segment_command_64* seg = (struct segment_command_64*)cmd;
				printf("%16s: %016llx - %016llx\n", seg->segname, seg->vmaddr, seg->vmsize);
				break;
			}
			
			default:
				continue;
		}
	}
}

int main(int argc, char* argv[]) {
	if(argc < 2) {
		fprintf(stderr, "Usage: %s <mach-o file> [<mach-o file>...]\n", argv[0]);
		return 1;
	}
	
	/* Print segments of each file specified in the argument list */
	for(int i = 1; i < argc; i++) {
		if(i > 1) {
			printf("\n");
		}
		
		printf("%s:\n", argv[i]);
		
		/* Get an open file descriptor for mmap */
		int fd = open(argv[i], O_RDONLY);
		if(fd == -1) {
			perror(argv[i]);
			continue;
		}
		
		/* Get filesize for mmap */
		size_t filesize = lseek(fd, 0, SEEK_END);
		lseek(fd, 0, SEEK_SET);
		
		/* Map the file */
		void* map = mmap(NULL, filesize, PROT_READ, MAP_PRIVATE, fd, 0);
		if(map == MAP_FAILED) {
			perror("mmap");
			close(fd);
			continue;
		}
		
		/* Attempt to print its segment names */
		print_segment_names(map, filesize);
		
		/* Clean up */
		munmap(map, filesize);
		close(fd);
	}
	
	return 0;
}