Re: varargs, 64-bit targets, and strict-aliasing warnings

["Joseph S. Myers" <jsm at polyomino dot org dot uk>]

On Thu, 26 Aug 2004, Roland Dreier wrote:

> 	int foo(int a, ...);
> 	
> 	int bar(void)
> 	{
> 		uint64_t x;
> 		return foo(1, (unsigned long long *) &x);
> 	}
> 
> If I compile for a 64-bit target with "-c -fstrict-aliasing -Wall", I get:
> 
> 	b.c: In function `bar':
> 	b.c:8: warning: dereferencing type-punned pointer will break strict-aliasing rules

uint64_t is unsigned long rather than unsigned long long on those 64-bit 
targets.  Thus the pointer cast creates a pointer which foo cannot safely 
dereference without converting back to a pointer to uint64_t.

-- 
Joseph S. Myers               http://www.srcf.ucam.org/~jsm28/gcc/
    jsm@polyomino.org.uk (personal mail)
    jsm28@gcc.gnu.org (Bugzilla assignments and CCs)