Question

 int test_malloc(void **ptr, size_t size)
 {
    (*ptr) = malloc(size);
    return 0;
 }

 int test_app()
 {
   char *data = NULL;
   int ret = 0;
   ret = test_malloc((void **)&data, 100);
 }

Compiler: gcc 4.1.2

Among others, I am using -O2 & -Wall which are I think are turning on some options which checks for this.

Answer 1

You have a variable of type char*, and in test_malloc you are modifying it through an lvalue of type void *, which breaks strict aliasing rules.

You could solve it like this:

 int test_app()
 {
   char *data = NULL;
   void *void_data = NULL;
   int ret = 0;
   ret = test_malloc(&void_data, 100);
   data = (char*)void_data;
 }

But even better is to make test_malloc return void* to avoid problems like this.