On 07/19/2015 01:25 PM, Rasmus Villemoes wrote:
On Sun, Jul 19 2015, Guenter Roeck <li...@roeck-us.net> wrote:
On Sun, Jul 19, 2015 at 02:20:14PM +0200, Sowmini Varadhan wrote:
Using a 64 bit constant generates "warning: integer constant is too
large for 'long' type" on 32 bit platforms. Instead use ~0l to get
the desired effect.
Detected by Andrew Morton who has confirmed that this patch
fixes the warning on i386/gcc-4.4.3, i386/gcc-4.4.0 and arm/gcc-4.4.4.
Signed-off-by: Sowmini Varadhan <sowmini.varad...@oracle.com>
---
lib/iommu-common.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/lib/iommu-common.c b/lib/iommu-common.c
index df30632..fd1297d 100644
--- a/lib/iommu-common.c
+++ b/lib/iommu-common.c
@@ -119,7 +119,7 @@ unsigned long iommu_tbl_range_alloc(struct device *dev,
unsigned long align_mask = 0;
if (align_order > 0)
- align_mask = 0xffffffffffffffffl >> (64 - align_order);
+ align_mask = ~0l >> (64 - align_order);
Wonder if this just hides the real problem. Unless align_order
is very large, the resulting mask on 32 bit systems may be 0.
Is this really the idea ?
Probably not, but that's not what would happen on x86: the shift
only depends on the lower 5 or 6 bits - I don't know if other platforms
also has that behaviour. So for align_order == 2 and x86_32 we'd
effectively end up with a shift of 62 & 31 == 30 (though technically
undefined behaviour), and the desired mask of 0x3.
#include <stdio.h>
main(int argc, char **argv)
{
unsigned long am1, am2, am3;
int align_order = 2;
am1 = 0xffffffffffffffffl >> (64 - align_order);
am2 = ~0l >> (64 - align_order);
am3 = ~0ul >> (64 - align_order);
printf("0x%lx 0x%lx 0x%lx\n", am1, am2, am3);
}
yields an output of
0x3 0xffffffffffffffff 0x3
So either case ~0l appears to be wrong; it should be ~0ul.
I don't know if ~0ull makes a difference for some architectures.
Guenter
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
