linux-kernel - [PATCH] fix sparse warning from include/linux/mmzone.h

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 07 Feb 2008 12:52:23 -0800
From:	Harvey Harrison <harvey.harrison@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...IV.linux.org.uk>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: [PATCH] fix sparse warning from include/linux/mmzone.h

include/linux/mmzone.h:640:22: warning: potentially expensive pointer subtraction

The code in question was doing a pointer subtraction to find the index of
the zone argument in the node_zones array.  This essentially boils down to:

((unsigned long)zone - (unsigned long)zone->zone_pgdat->node_zones)/sizeof(struct zone)

Which can be expensive if struct zone is not a power of two.  Instead, just
calculate the offsets rather than the index in the array.

Signed-off-by: Harvey Harrison <harvey.harrison@...il.com>
---
This shows up > 30 times in an x86 allyesconfig, would be nice to get
rid of it and makes the code a little more efficient.  I believe this
is correct, unless there is a subtlety I have missed.

 include/linux/mmzone.h |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 8d8d197..cb07758 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -637,9 +637,12 @@ static inline int is_normal_idx(enum zone_type idx)
 static inline int is_highmem(struct zone *zone)
 {
 #ifdef CONFIG_HIGHMEM
-	int zone_idx = zone - zone->zone_pgdat->node_zones;
-	return zone_idx == ZONE_HIGHMEM ||
-		(zone_idx == ZONE_MOVABLE && zone_movable_is_highmem());
+	const int highmem_off = ZONE_HIGHMEM * sizeof(*zone);
+	const int movable_off = ZONE_MOVABLE * sizeof(*zone);
+
+	int zone_off = (unsigned long)zone - (unsigned long)zone->zone_pgdat->node_zones;
+	return zone_off == highmem_off ||
+		(zone_off == movable_off && zone_movable_is_highmem());
 #else
 	return 0;
 #endif
-- 
1.5.4.1219.g65b9



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/