[igt-dev] [PATCH i-g-t 1/2] lib: Beware implicit sign extension on large constants

[Zbigniew Kempczyński]

On Mon, Jun 21, 2021 at 12:59:21PM +0200, Zbigniew Kempczyński wrote:
> From: Chris Wilson <chris.p.wilson at intel.com>
> 
> (gdb) p/x (long long unsigned int)(1 << 31)
> $1 = 0xffffffff80000000
> (gdb) p/x (long long unsigned int)(1u << 31)
> $2 = 0x80000000
> 
> The impact of this is that the random address we were placing the spinner
> at was always invalid on modern machines, causing the kernel to relocate
> the spinners wherever and thus undergoing relocations.
> 
> Signed-off-by: Chris Wilson <chris.p.wilson at intel.com>

We have same observation and we want to fix that.

Reviewed-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>

--
Zbigniew

> ---
>  lib/igt_dummyload.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/igt_dummyload.c b/lib/igt_dummyload.c
> index 82459e524..63b1fc73b 100644
> --- a/lib/igt_dummyload.c
> +++ b/lib/igt_dummyload.c
> @@ -119,7 +119,7 @@ emit_recursive_batch(igt_spin_t *spin,
>  	 */
>  	addr = gem_aperture_size(fd) / 2;
>  	if (addr >> 31)
> -		addr = 1 << 31;
> +		addr = 1u << 31;
>  	addr += random() % addr / 2;
>  	addr &= -4096;
>  
> -- 
> 2.26.0
> 
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