int main()
{
void *handle = 0; //handle to store hook-related info
mach_substitution original; //original data for restoration
Dl_info info;
if (!dladdr((void const *)libtest, &info)) //gets an address and a path of a target library
{
fprintf(stderr, "Failed to get the base address of a library at `%s`!\n", info.dli_fname);
goto end;
}
handle = mach_hook_init(info.dli_fname, info.dli_fbase);
if (!handle)
{
fprintf(stderr, "Redirection init failed!\n");
goto end;
}
libtest(); //calls puts() from libSystem.B.dylib
puts("-----------------------------");
original = mach_hook(handle, "puts", (mach_substitution)hooked_puts);
if (!original)
{
fprintf(stderr, "Redirection failed!\n");
goto end;
}
libtest(); //calls hooked_puts()
puts("-----------------------------");
original = mach_hook(handle, "puts", original); //restores the original relocation
if (!original)
{
fprintf(stderr, "Restoration failed!\n");
goto end;
}
libtest(); //again calls puts() from libSystem.B.dylib
end:
mach_hook_free(handle);
handle = 0; //no effect here, but just a good advice to prevent double freeing
return 0;
}
static void *
elf_hook(char const *libpath, void const *unused, char const *name, void const *func) {
#if 1
return NULL;
#else
void *libaddr, *handle, *first;
char *ptr;
Dl_info info;
FILE *fp;
char cmd[1024];
// find one function from libpath
snprintf(cmd, sizeof(cmd), "nm %s | grep ' T ' | head -n 2", libpath);
if((fp = popen(cmd, "r")) == NULL)
return NULL;
if(fgets(cmd, sizeof(cmd), fp) == NULL) {
pclose(fp);
return NULL;
}
pclose(fp);
// move to end
for(ptr = cmd; *ptr; ptr++)
;
// seek for the last ' ' or '\t'
for(--ptr; ptr >= cmd; ptr--) {
if(*ptr==0x0d || *ptr==0x0a) {
*ptr = '\0';
}
if(*ptr==' ' || *ptr=='\t') {
*ptr++ = '\0';
if(*ptr == '_')
*ptr++ = '\0';
break;
}
}
// get the function address
ga_error("Retrieve base address via function '%s' from %s\n",
ptr, libpath);
if((handle = dlopen(libpath, RTLD_LAZY)) == NULL)
return NULL;
if((first = dlsym(handle, ptr)) == NULL)
return NULL;
//
if(dladdr((void const *) first, &info) == 0)
return NULL;
libaddr = mach_hook_init(libpath, info.dli_fbase);
if(libaddr == NULL)
return NULL;
return (void*) mach_hook(libaddr, name, (mach_substitution) func);
#endif
}
