swift-dlsym.m

#include <mach-o/dyld.h>
#include <mach-o/loader.h>
#include <mach-o/nlist.h>
#include <mach-o/dyld_images.h>
#include <dlfcn.h>

static void *dyld_for_each_installed_shared_cache;
static void *dyld_shared_cache_for_each_image;
static void *dyld_image_get_installname;
static void *dyld_image_local_nlist_content_4Symbolication;

static const char *swift_demangle(const char *mangled_name) {
    
    static void *swift_demangle_ptr = NULL;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        swift_demangle_ptr = dlsym(RTLD_DEFAULT, "swift_demangle");
    });
    
    if (swift_demangle_ptr == NULL || mangled_name == NULL) {
        return NULL;
    }

    size_t output_size = 0;
    return ((char *(*)(const char *, size_t, char *, size_t *, uint32_t))swift_demangle_ptr)(mangled_name, strlen(mangled_name), NULL, &output_size, 0);
}

static void *swift_dlsym(const char *symbol_name) {
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        void *handle = dlopen("/usr/lib/system/libdyld.dylib", RTLD_LAZY);
        dyld_for_each_installed_shared_cache = dlsym(handle, "dyld_for_each_installed_shared_cache");
        dyld_shared_cache_for_each_image = dlsym(handle, "dyld_shared_cache_for_each_image");
        dyld_image_get_installname = dlsym(handle, "dyld_image_get_installname");
        dyld_image_local_nlist_content_4Symbolication = dlsym(handle, "dyld_image_local_nlist_content_4Symbolication");
    });
    

    __block void *found_symbol = NULL;
    
    ((void (*)(void (^)(void *)))dyld_for_each_installed_shared_cache)(^(void *cache) {
        ((void (*)(void *, void (^)(void *)))dyld_shared_cache_for_each_image)(cache, ^(void *image) {
            ((bool (*)(void *, void (^)(const void *, uint64_t, const char *)))
             dyld_image_local_nlist_content_4Symbolication)(image, ^(const void *nlistStart, uint64_t nlistCount, const char *stringTable) {
                
                const struct nlist_64 *symTab = (const struct nlist_64 *)nlistStart;
                for (uint64_t i = 0; i < nlistCount && !found_symbol; i++) {
                    const char *mangled_name = &stringTable[symTab[i].n_un.n_strx];
                    if (symTab[i].n_un.n_strx == 0) {
                        continue;
                    }
                    
                    if (strcmp(mangled_name, symbol_name) == 0) {
                        found_symbol = (void *)symTab[i].n_value;
                        return;
                    }
                    
                    if (mangled_name[0] == '_' && strcmp(mangled_name + 1, symbol_name) == 0) {
                        found_symbol = (void *)symTab[i].n_value;
                        return;
                    }
                    
                    const char *demangled = swift_demangle(mangled_name);
                    if (demangled) {
                        if (strstr(demangled, symbol_name)) {
                            found_symbol = (void *)symTab[i].n_value;
                            printf("'%s' matched to:\n  mangled: %s\n  demangled: %s\n", symbol_name, mangled_name, demangled);
                        }
                        free((void *)demangled);
                    }
                    
                    if (found_symbol) {
                        return;
                    }
                }
            });
        });
    });
    
    return found_symbol;
}