Casting 64-bit pointers to integers

Casting 64-bit pointers to integers

[Michael David Crawford]

In building on my 64-bit Xeon box, I see a lot of warnings about casting 
between pointers and integers of different sizes.

Sometimes it can cause fatal compiler error.

Is there a reasonably portable way to make such casts?

The conventional wisdom is that ints are supposed to be the natural 
machine word size.  But even that isn't always the case - much gnashing 
of teeth resulted in the two most popular compilers for the 68000 
Macintosh having different int sizes.

There are typedefs for integers with specific numbers of bits, but 
that's not what we want.  If we're building for 32-bit, we want a 32-bit 
integer, and if we're building for 64-bit, we want a 64-bit integer.

Is there any kind of standardized integer type which is guaranteed to be 
the same size as a pointer?

What might even be worse is that the mismatch is on purpose for some 
reason, say that some structure has a field that simply *must* be 
32-bits, but we're trying to wedge a 64-bit pointer into it.

Mike
-- 
Michael David Crawford
mdc@prgmr.com

    prgmr.com - We Don't Assume You Are Stupid.

       Xen-Powered Virtual Private Servers: http://prgmr.com/xen

Re: Casting 64-bit pointers to integers

[Samuel Thibault]

Michael David Crawford, le Fri 22 May 2009 02:30:35 -0700, a écrit :
> There are typedefs for integers with specific numbers of bits, but 
> that's not what we want.  If we're building for 32-bit, we want a 32-bit 
> integer, and if we're building for 64-bit, we want a 64-bit integer.

intptr_t/uintptr_t is there for this.

Samuel

Re: Casting 64-bit pointers to integers

[Michael David Crawford]

Samuel Thibault wrote:
> intptr_t/uintptr_t is there for this.

In tools/xenpmd/acpi-events.c, which is in the git sources but doesn't 
seem to be in the 3.4 sources, there are two returns from 
acpi_events_thread which cast ints to void*'s.  These break the compile 
on 64-bit.

One of the ints is a socket_fd, the other is the result from a connect 
system call.

I got it to compile at first by doing something like this:

   return (void*)(unsigned long long)socket_fd

But what would be better is

   return (void*)(uintptr_t)socket_fd

If you were to just make socket_fd a uintptr_t, it would lose precision 
when you passed it to connect.  You could explicitly cast it to an int 
there, I suppose.

Mike

-- 
Michael David Crawford
mdc@prgmr.com

    prgmr.com - We Don't Assume You Are Stupid.

       Xen-Powered Virtual Private Servers: http://prgmr.com/xen

Re: Casting 64-bit pointers to integers

[Samuel Thibault]

Michael David Crawford, le Fri 22 May 2009 02:53:38 -0700, a écrit :
> But what would be better is
> 
>   return (void*)(uintptr_t)socket_fd

Yes, that's the correct way.

Samuel