Exchange Mach-O platform types with min version

platform_swap.m

//
//  main.m
//  platform_swap @LOLgrep
//

#import <Foundation/Foundation.h>
#import <mach-o/loader.h>

#define PLATFORM_VISIONOS 11
#define PLATFORM_VISIONOSSIMULATOR 12

struct version {
    int fix : 8;
    int min : 8;
    int max : 16;
};

int main(int argc, const char * argv[]) {
    
    if (argc != 6) {
        printf("platform_swap platform_num major minor bugfix (i.e. convert MacOS M1 binary to iOS 10.3.1 -> platform_swap /tmp/afile 2 10 3 1\nSee PLATFORM_* in <mach-o/loader.h>\n");
        exit(1);
    }
    
    long platform = strtol(argv[2], NULL, 12);
    if ( platform < 1 || platform > 12 ) {
        printf("Invalid platform number %ld\n", platform);
        exit(1);
    }
    
    long major  = strtol(argv[3], NULL, 12);
    long minor  = strtol(argv[4], NULL, 12);
    long bugfix = strtol(argv[5], NULL, 12);
    
    NSString *file = [NSString stringWithUTF8String:argv[1]];
    NSURL *fileURL = [NSURL fileURLWithPath:file];
    
    if (!fileURL) {
        printf("Can't find file %s\n", argv[1]);
        exit(1);
    }
    
    NSMutableData *data = [NSMutableData dataWithContentsOfFile:file];
    char *ptr = (void*)[data bytes];
    int32_t *magic = (int32_t*)ptr;
    
    if (*magic != MH_MAGIC_64) {
        printf("Invalid header file\n");
        exit(1);
    }
    
    struct mach_header_64 *header = (void*)ptr;
    struct load_command *cur = (void*)((uintptr_t)ptr + (uintptr_t)sizeof(struct mach_header_64));
    
    for (int i = 0; i < header->ncmds; i++) {
        if (cur->cmd == LC_BUILD_VERSION) {
            struct build_version_command*build = (void*)cur;
            NSRange platform_range = NSMakeRange((uintptr_t)&build->platform - (uintptr_t)ptr, sizeof(build->platform));
            int32_t new_platform = (int)platform;
            [data replaceBytesInRange:platform_range withBytes:&new_platform];
            
            NSRange version_range = NSMakeRange((uintptr_t)&build->minos - (uintptr_t)ptr, sizeof(build->minos));
            struct version new_version = {(int)bugfix, (int)minor, (int)major};
            [data replaceBytesInRange:version_range withBytes:&new_version];
            char *platform_name = NULL;
            switch (platform) {
                case PLATFORM_MACOS:
                    platform_name = "macos";
                    break;
                case PLATFORM_IOS:
                    platform_name = "ios";
                    break;
                case PLATFORM_TVOS:
                    platform_name = "tvos";
                    break;
                case PLATFORM_WATCHOS:
                    platform_name = "watchos";
                    break;
                case PLATFORM_BRIDGEOS:
                    platform_name = "bridgeos";
                    break;
                case PLATFORM_MACCATALYST:
                    platform_name = "maccatalyst";
                    break;
                case PLATFORM_IOSSIMULATOR:
                    platform_name = "iossimulator";
                    break;
                case PLATFORM_TVOSSIMULATOR:
                    platform_name = "tvossimulator";
                    break;
                case PLATFORM_WATCHOSSIMULATOR:
                    platform_name = "watchossimulator";
                    break;
                case PLATFORM_DRIVERKIT:
                    platform_name = "driverkit";
                    break;
                case PLATFORM_VISIONOS:
                    platform_name = "visionos";
                    break;
                case PLATFORM_VISIONOSSIMULATOR:
                    platform_name = "visionossimulator";
                    break;
                default:
                    break;
            }
            NSString *resolvedString = [NSString stringWithFormat:@"%@_%s", file, platform_name];
            [data writeToFile:resolvedString atomically:YES];
            printf("written to \"%s\"\n", resolvedString.UTF8String);
            
            exit(0);
        }
        
        cur = (void*)(cur->cmdsize  + (uintptr_t)cur);
    }
    
    return 0;
}