strict aliasing question

[Howard Chu <hyc at highlandsun dot com>]

I see a lot of APIs (e.g. Cyrus SASL) that have accessor functions 
returning values through a void ** argument. As far as I can tell, this 
doesn't actually cause any problems, but gcc 4.1 with -Wstrict-aliasing 
will complain. For example, take these two separate source files:

alias1.c
####

#include <stdio.h>

extern void getit( void **arg );

main() {
       int *foo;

       getit( (void **)&foo);
       printf("foo: %x\n", *foo);
}
####


alias2.c
####
static short x[] = {16,16};

void getit( void **arg ) {
       *arg = x;
}
####

gcc -O3 -fstrict-aliasing -Wstrict-aliasing *.c -o alias

The program prints the expected result with both strict-aliasing and 
no-strict-aliasing on my x86_64 box.  As such, when/why would I need to 
worry about  this warning?

--
 -- Howard Chu
 Chief Architect, Symas Corp.  http://www.symas.com
 Director, Highland Sun        http://highlandsun.com/hyc
 OpenLDAP Core Team            http://www.openldap.org/project/