Function to get the image_vmaddr_slide of a mach_header

mach_slide.c

//
//  mach_slide.c
//
//  This code was based on functions from https://opensource.apple.com/source/dyld
//  See the Apple Public Source License https://www.opensource.apple.com/apsl
//
//  Created by Leptos on 5/11/19.
//

#include <string.h>
#include <mach-o/loader.h>

/* modified from dyld/src/ImageLoaderMachO.cpp
 *
 * these functions are almost identitical, so notes are here:
 *   the first load command immediate follows the header
 *   to access that location, dyld does `(char *)mh + sizeof(struct mach_header[_64])`
 *   to be more generic, I would write this as `(char *)mh + sizeof(*mh)`
 *   the other thing you can do is `mh + 1`, because it's compiled equivalent to the above line
 *   that's also equivalent to `&mh[1]` ("expands" to `&(*(mh + 1))` which is `mh + 1`)
 *   because `&mh[1]` doesn't require additional parentheses to cast, it's the one used below
 */

/// The address slide of an image for a given mach_header
intptr_t mach_header_compute_slide(struct mach_header const *const mh) {
    struct segment_command const *seg = (__typeof(seg))&mh[1];
    for (uint32_t cmdi = 0; cmdi < mh->ncmds; seg = (void *)seg + seg->cmdsize, cmdi++) {
        if ((seg->cmd == LC_SEGMENT) && (strcmp(seg->segname, SEG_TEXT) == 0)) {
            return (intptr_t)mh - seg->vmaddr;
        }
    }
    return 0;
}

/// The address slide of an image for a given mach_header_64
intptr_t mach_header_compute_slide_64(struct mach_header_64 const *const mh) {
    struct segment_command_64 const *seg = (__typeof(seg))&mh[1];
    for (uint32_t cmdi = 0; cmdi < mh->ncmds; seg = (void *)seg + seg->cmdsize, cmdi++) {
        if ((seg->cmd == LC_SEGMENT_64) && (strcmp(seg->segname, SEG_TEXT) == 0)) {
            return (intptr_t)mh - seg->vmaddr;
        }
    }
    return 0;
}