Re: [PATCH] Fix compilation warning on 64 bits platforms

[Josh Triplett <josh@freedesktop.org>]

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Damien Lespiau wrote:
> Fix: format '%d' expects type 'int', but argument 2 has type 'long int'
[...]
> @@ -461,7 +461,7 @@ const char *show_instruction(struct instruction *insn)
>  	}
>  
>  	if (buf >= buffer + sizeof(buffer))
> -		die("instruction buffer overflowed %d\n", buf - buffer);
> +		die("instruction buffer overflowed %d\n", (int)(buf - buffer));

A cast doesn't seem like the right fix.  The difference between two pointers
has type ptrdiff_t.  sizeof(ptrdiff_t) == 8 on 64-bit platforms, leading to
the legitimate warning you saw.  This cast would truncate the difference to 32
bits.  glibc supplies a "t" length modifier for ptrdiff_t, but I don't think
sparse can't portably use that.  I don't think we can portably use %llu
either, even though we use long long.  On the other hand, sparse already seems
to use %llu.

Obviously 32-bit overflow seems unlikely here, but I don't like using a cast
to shut GCC up when it has a legitimate complaint; I'd prefer to have the
right fix.

The ideal fix, so we don't have to worry about printf format-string
portability: change this function to cleanly *prevent* instruction buffer
overflows rather than detecting them after the fact. :)

- Josh Triplett



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