Merge pull request facebook#18 from uroboro/master

Save previous pointer automatically

README.md

@@ -18,11 +18,6 @@ Once you add `fishhook.h`/`fishhook.c` to your project, you can rebind symbols a
 static int (*orig_close)(int);
 static int (*orig_open)(const char *, int, ...);
 
-void save_original_symbols() {
-  orig_close = dlsym(RTLD_DEFAULT, "close");
-  orig_open = dlsym(RTLD_DEFAULT, "open");
-}
-
 int my_close(int fd) {
   printf("Calling real close(%d)\n", fd);
   return orig_close(fd);
@@ -48,8 +43,7 @@ int my_open(const char *path, int oflag, ...) {
 int main(int argc, char * argv[])
 {
   @autoreleasepool {
-    save_original_symbols();
-    rebind_symbols((struct rebinding[2]){{"close", my_close}, {"open", my_open}}, 2);
+    rebind_symbols((struct rebinding[2]){{"close", my_close, (void *)&orig_close}, {"open", my_open, (void *)&orig_open}}, 2);
 
     // Open our own binary and print out first 4 bytes (which is the same
     // for all Mach-O binaries on a given architecture)

fishhook.c

@@ -97,6 +97,10 @@ static void perform_rebinding_with_section(struct rebindings_entry *rebindings,
       for (uint j = 0; j < cur->rebindings_nel; j++) {
         if (strlen(symbol_name) > 1 &&
             strcmp(&symbol_name[1], cur->rebindings[j].name) == 0) {
+          if (cur->rebindings[j].replaced != NULL &&
+              indirect_symbol_bindings[i] != cur->rebindings[j].replacement) {
+            *(cur->rebindings[j].replaced) = indirect_symbol_bindings[i];
+          }
           indirect_symbol_bindings[i] = cur->rebindings[j].replacement;
           goto symbol_loop;
         }

fishhook.h

@@ -38,6 +38,7 @@ extern "C" {
 struct rebinding {
   const char *name;
   void *replacement;
+  void **replaced;
 };
 
 /*