linux-kernel - [PATCH 1/4] lib/vsprintf.c: Eliminate some branches

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

Message-Id: <1424474479-25543-2-git-send-email-linux@rasmusvillemoes.dk>
Date:	Sat, 21 Feb 2015 00:21:16 +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 1/4] lib/vsprintf.c: Eliminate some branches

Since FORMAT_TYPE_INT is simply 1 more than FORMAT_TYPE_UINT, and
similarly for BYTE/UBYTE, SHORT/USHORT, LONG/ULONG, we can eliminate a
few instructions by making SIGN have the value 1 instead of 2, and
then use arithmetic instead of branches for computing the right
spec->type. It's a little hacky, but certainly in the same spirit as
SMALL needing to have the value 0x20. For example for the
spec->qualifier == 'l' case, gcc now generates

     75e:       0f b6 53 01             movzbl 0x1(%rbx),%edx
     762:       83 e2 01                and    $0x1,%edx
     765:       83 c2 09                add    $0x9,%edx
     768:       88 13                   mov    %dl,(%rbx)

instead of

     763:       0f b6 53 01             movzbl 0x1(%rbx),%edx
     767:       83 e2 02                and    $0x2,%edx
     76a:       80 fa 01                cmp    $0x1,%dl
     76d:       19 d2                   sbb    %edx,%edx
     76f:       83 c2 0a                add    $0xa,%edx
     772:       88 13                   mov    %dl,(%rbx)

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 lib/vsprintf.c | 30 +++++++++++-------------------
 1 file changed, 11 insertions(+), 19 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index b235c96167d3..318d583fe862 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -340,8 +340,8 @@ int num_to_str(char *buf, int size, unsigned long long num)
 	return len;
 }
 
-#define ZEROPAD	1		/* pad with zero */
-#define SIGN	2		/* unsigned/signed long */
+#define SIGN	1		/* unsigned/signed, must be 1 */
+#define ZEROPAD	2		/* pad with zero */
 #define PLUS	4		/* show plus */
 #define SPACE	8		/* space if plus */
 #define LEFT	16		/* left justified */
@@ -447,7 +447,7 @@ char *number(char *buf, char *end, unsigned long long num,
 		spec.precision = i;
 	/* leading space padding */
 	spec.field_width -= spec.precision;
-	if (!(spec.flags & (ZEROPAD+LEFT))) {
+	if (!(spec.flags & (ZEROPAD | LEFT))) {
 		while (--spec.field_width >= 0) {
 			if (buf < end)
 				*buf = ' ';
@@ -1738,29 +1738,21 @@ qualifier:
 	if (spec->qualifier == 'L')
 		spec->type = FORMAT_TYPE_LONG_LONG;
 	else if (spec->qualifier == 'l') {
-		if (spec->flags & SIGN)
-			spec->type = FORMAT_TYPE_LONG;
-		else
-			spec->type = FORMAT_TYPE_ULONG;
+		BUILD_BUG_ON(FORMAT_TYPE_ULONG + SIGN != FORMAT_TYPE_LONG);
+		spec->type = FORMAT_TYPE_ULONG + (spec->flags & SIGN);
 	} else if (_tolower(spec->qualifier) == 'z') {
 		spec->type = FORMAT_TYPE_SIZE_T;
 	} else if (spec->qualifier == 't') {
 		spec->type = FORMAT_TYPE_PTRDIFF;
 	} else if (spec->qualifier == 'H') {
-		if (spec->flags & SIGN)
-			spec->type = FORMAT_TYPE_BYTE;
-		else
-			spec->type = FORMAT_TYPE_UBYTE;
+		BUILD_BUG_ON(FORMAT_TYPE_UBYTE + SIGN != FORMAT_TYPE_BYTE);
+		spec->type = FORMAT_TYPE_UBYTE + (spec->flags & SIGN);
 	} else if (spec->qualifier == 'h') {
-		if (spec->flags & SIGN)
-			spec->type = FORMAT_TYPE_SHORT;
-		else
-			spec->type = FORMAT_TYPE_USHORT;
+		BUILD_BUG_ON(FORMAT_TYPE_USHORT + SIGN != FORMAT_TYPE_SHORT);
+		spec->type = FORMAT_TYPE_USHORT + (spec->flags & SIGN);
 	} else {
-		if (spec->flags & SIGN)
-			spec->type = FORMAT_TYPE_INT;
-		else
-			spec->type = FORMAT_TYPE_UINT;
+		BUILD_BUG_ON(FORMAT_TYPE_UINT + SIGN != FORMAT_TYPE_INT);
+		spec->type = FORMAT_TYPE_UINT + (spec->flags & SIGN);
 	}
 
 	return ++fmt - start;
-- 
2.1.3

--
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/