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

[Zbigniew Kempczyński]

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>
---
 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