From: Roland McGrath <roland@hack.frob.com>
To: libc-ports@sourceware.org
Subject: [PATCH roland/arm-strlen] Make armv6t2 strlen work in ARM mode too.
Date: Fri, 30 Aug 2013 18:06:00 -0000 [thread overview]
Message-ID: <20130830180620.77DD12C072@topped-with-meat.com> (raw)
I tested that this has no effect (assembled code wholly unchanged) on
arm-linux-gnueabihf. I tested that the ARM-mode support actually works by
hacking in "#define NO_THUMB" at the top and verifying no failures from
'make check subdirs=string'.
Incidentally, assembly writers really ought to write more comments! For
example, I deduced the only plausible reason for using an explicit bne.w
and added a comment about it, but it is exactly the sort of non-obvious
subtle microoptimization that desperately needed clear comments in the
first place.
OK for trunk?
Thanks,
Roland
ports/ChangeLog.arm
2013-08-30 Roland McGrath <roland@hack.frob.com>
* sysdeps/arm/armv6t2/strlen.S: Include <arm-features.h> first thing.
[NO_THUMB]: Adapt code for ARM mode.
--- a/ports/sysdeps/arm/armv6t2/strlen.S
+++ b/ports/sysdeps/arm/armv6t2/strlen.S
@@ -21,6 +21,7 @@
*/
+#include <arm-features.h> /* This might #define NO_THUMB. */
#include <sysdep.h>
#ifdef __ARMEB__
@@ -31,9 +32,24 @@
#define S2HI lsl
#endif
- /* This code requires Thumb. */
+#ifndef NO_THUMB
+/* This code is best on Thumb. */
.thumb
- .syntax unified
+#else
+/* Using bne.w explicitly is desirable in Thumb mode because it helps
+ align the following label without a nop. In ARM mode there is no
+ such difference. */
+.macro bne.w label
+ bne \label
+.endm
+
+/* This clobbers the condition codes, which the real Thumb cbnz instruction
+ does not do. But it doesn't matter for any of the uses here. */
+.macro cbnz reg, label
+ cmp \reg, #0
+ bne \label
+.endm
+#endif
/* Parameters and result. */
#define srcin r0
@@ -130,9 +146,16 @@ ENTRY(strlen)
tst tmp1, #4
pld [src, #64]
S2HI tmp2, const_m1, tmp2
+#ifdef NO_THUMB
+ mvn tmp1, tmp2
+ orr data1a, data1a, tmp1
+ itt ne
+ orrne data1b, data1b, tmp1
+#else
orn data1a, data1a, tmp2
itt ne
ornne data1b, data1b, tmp2
+#endif
movne data1a, const_m1
mov const_0, #0
b .Lstart_realigned
next reply other threads:[~2013-08-30 18:06 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-30 18:06 Roland McGrath [this message]
2013-08-30 20:36 ` Joseph S. Myers
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