linux-kernel - [PATCH 2/4] lib/vsprintf.c: Reduce stack use in number()

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Date:	Sat, 21 Feb 2015 00:21:17 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 2/4] lib/vsprintf.c: Reduce stack use in number()

At least since the initial git commit, when base was passed as a
separate parameter, number() has only been called with bases 8, 10 and
16. I'm guessing that 66 was to accommodate 64 0/1, a sign and a '\0',
but the buffer is only used for the actual digits. Octal digits carry
3 bits of information, so 24 is enough. Spell that 3*sizeof(num) so
one less place needs to be changed should long long ever be 128
bits. Also remove the commented-out code that would handle an
arbitrary base.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 lib/vsprintf.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 318d583fe862..98f1ce907d3d 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -386,7 +386,7 @@ char *number(char *buf, char *end, unsigned long long num,
 	/* we are called with base 8, 10 or 16, only, thus don't need "G..."  */
 	static const char digits[16] = "0123456789ABCDEF"; /* "GHIJKLMNOPQRSTUVWXYZ"; */
 
-	char tmp[66];
+	char tmp[3 * sizeof(num)];
 	char sign;
 	char locase;
 	int need_pfx = ((spec.flags & SPECIAL) && spec.base != 10);
@@ -423,11 +423,6 @@ char *number(char *buf, char *end, unsigned long long num,
 	i = 0;
 	if (num < spec.base)
 		tmp[i++] = digits[num] | locase;
-	/* Generic code, for any base:
-	else do {
-		tmp[i++] = (digits[do_div(num,base)] | locase);
-	} while (num != 0);
-	*/
 	else if (spec.base != 10) { /* 8 or 16 */
 		int mask = spec.base - 1;
 		int shift = 3;
-- 
2.1.3

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