Exchange Mach-O platform types with min version

platform_swap.m

//
//  main.m
//  platform_swap @LOLgrep
//  clang -o /tmp/platform_swap /path/to/platform_swap.m -framework Foundation

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

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

static const char *get_platform_str(int platform) {
    switch (platform) {
        case PLATFORM_MACOS:
            return  "macos";
        case PLATFORM_IOS:
            return  "ios";
        case PLATFORM_TVOS:
            return  "tvos";
        case PLATFORM_WATCHOS:
            return "watchos";
        case PLATFORM_BRIDGEOS:
            return  "bridgeos";
        case PLATFORM_MACCATALYST:
            return "maccatalyst";
        case PLATFORM_IOSSIMULATOR:
            return  "iossimulator";
        case PLATFORM_TVOSSIMULATOR:
            return  "tvossimulator";
        case PLATFORM_WATCHOSSIMULATOR:
            return  "watchossimulator";
        case PLATFORM_DRIVERKIT:
            return  "driverkit";
        case PLATFORM_ANY:
            return  "any";
        default:
            return "unkown";
    }
    return "unknown";
}

int main(int argc, const char * argv[]) {
    
    if (argc != 6 && argc != 2) {
        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);
    }
    
   

    
    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) {
        if (*magic == FAT_CIGAM || *magic == FAT_MAGIC || *magic == FAT_MAGIC_64 || *magic == FAT_CIGAM_64) {
            printf("fat file. Use \"lipo -thin <ARCH> -o /tmp/new_file %s\" first\n", argv[1]);
        }
        
        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));
    
    if (argc == 2) {
        for (int i = 0; i < header->ncmds; i++) {
            if (cur->cmd == LC_BUILD_VERSION) {
                struct build_version_command* build = (void*)cur;
                struct version *v = (void*)&build->minos;
                struct version *sdk = (void*)&build->sdk;
                printf("%s (%d) %d.%d.%d, built with sdk: %d.%d.%d\nplatform_swap %s %d %d %d %d\n", get_platform_str(build->platform), build->platform, v->max, v->min, v->fix, sdk->max, sdk->min, sdk->fix, argv[1], build->platform, v->max, v->min
                       , v->fix);
                exit(0);
            }
            cur = (void*)(cur->cmdsize  + (uintptr_t)cur);
        }
        printf("couldn't find LC_BUILD_VERSION\n");
        exit(1);
    }
    
    long platform = strtol(argv[2], NULL, 10);
    long major  = strtol(argv[3], NULL, 10);
    long minor  = strtol(argv[4], NULL, 10);
    long bugfix = strtol(argv[5], NULL, 10);
    
    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];
            const char *platform_name = get_platform_str(build->platform);
          
            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;
}