[PATCH v6] arm: use built-in byte swap function

[Kim Phillips <kim.phillips@freescale.com>]

On Thu, 21 Feb 2013 22:40:08 -0500
Nicolas Pitre <nico@fluxnic.net> wrote:

> On Thu, 21 Feb 2013, Kim Phillips wrote:
> 
> > Here's the asm version I'm working on now, based on compiler
> > output of the C version.  Haven't tested beyond defconfig builds,
> > which pass ok.
> > 
> > Is there anything I have to do for thumb mode?  If so, how to test?
> 
> You just need to pick a config that uses some ARMv7 processor, and 
> enable CONFIG_THUMB2_KERNEL.  I don't see any problem with your patch 
> wrt Thumb2.

ok, I've addressed your comments and tested both pre-armv6 and armv6
+ bswapsi2s on i.mx hardware with CONFIG_CC_OPTIMIZE_FOR_SIZE and
CONFIG_THUMB2_KERNEL set:

>From c22f4050174d8da71fdddba2cf67ae40c00ca5cc Mon Sep 17 00:00:00 2001
From: Kim Phillips <kim.phillips@freescale.com>
Date: Tue, 19 Feb 2013 17:16:11 -0600
Subject: [PATCH] arm: use built-in byte swap function

Enable the compiler intrinsic for byte swapping on arch ARM.  This
allows the compiler to detect and be able to optimize out byte
swappings, and has a tiny benefit on vmlinux size (Linaro gcc 4.7.3):

   text	   data	    bss	    dec	    hex	filename
2754100	 121144	  56520	2931764	 2cbc34	vmlinux-lart #orig
2754050	 121144	  56520	2931714	 2cbc02	vmlinux-lart #builtin-bswap
6282699	 307852	5578076	12168627 b9adb3	vmlinux-mxs #orig
6282241	 307832	5578076	12168149 b9abd5	vmlinux-mxs #builtin-bswap
7200193	 364180	 361748	7926121	 78f169	vmlinux-imx_v6_v7 #orig
7199515	 364188	 361748	7925451	 78eecb	vmlinux-imx_v6_v7 #builtin-bswap

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
---
akin to: http://comments.gmane.org/gmane.linux.kernel.cross-arch/16016

based on linux-next-20130221.

changes from last diff:
- addressed Nicolas' comments
- updated commit text figures and reformatted as a patch

changes from diff before that:
- 1st asm version

changes from diff before that:
- enforce -O2 for bswapsdi2.o
- fix building out-of-source tree

changes from diff before that:
- implement custom __bswap[sd]i2 in arch/arm/lib/bswapsdi2.c

v5: re-work based on new gcc version test data:
  - moved outside armv6 protection
  - check for gcc 4.6+ demoted to gcc 4.5+ with:
    !defined(CONFIG_CC_OPTIMIZE_FOR_SIZE)

v4:
- undo v2-2's addition of ARCH_DEFINES_BUILTIN_BSWAP per Boris
  and David - object is to find arches that define _HAVE_BSWAP
  and clean it up in the future: patch is much less intrusive. :)

v3:
- moved out of uapi swab.h into arch/arm/include/asm/swab.h
- moved ARCH_DEFINES_BUILTIN_BSWAP help text into commit message
- moved GCC_VERSION >= 40800 ifdef into GCC_VERSION >= 40600 block

v2:
- at91 and lpd270 builds fixed by limiting to ARMv6 and above
  (i.e., ARM cores that have support for the 'rev' instruction).
  Otherwise, the compiler emits calls to libgcc's __bswapsi2 on
  these ARMv4/v5 builds (and arch ARM doesn't link with libgcc).
  All ARM defconfigs now have the same build status as they did
  without this patch (some are broken on linux-next).

- move ARM check from generic compiler.h to arch ARM's swab.h.
  - pretty sure it should be limited to __KERNEL__ builds

- add new ARCH_DEFINES_BUILTIN_BSWAP (see Kconfig help).
  - if set, generic compiler header does not set HAVE_BUILTIN_BSWAPxx
  - not too sure about this having to be a new CONFIG_, but it's hard
    to find a place for it given linux/compiler.h doesn't include any
    arch-specific files.

- move new selects to end of CONFIG_ARM's Kconfig select list,
  as is done in David Woodhouse's original patchseries for ppc/x86.

 arch/arm/Kconfig                  |  1 +
 arch/arm/boot/compressed/Makefile | 15 +++++++++++----
 arch/arm/kernel/armksyms.c        |  4 ++++
 arch/arm/lib/Makefile             |  2 +-
 arch/arm/lib/bswapsdi2.S          | 36 ++++++++++++++++++++++++++++++++++++
 5 files changed, 53 insertions(+), 5 deletions(-)
 create mode 100644 arch/arm/lib/bswapsdi2.S

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index dedf02b..e8a41d0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -59,6 +59,7 @@ config ARM
 	select CLONE_BACKWARDS
 	select OLD_SIGSUSPEND3
 	select OLD_SIGACTION
+	select ARCH_USE_BUILTIN_BSWAP
 	help
 	  The ARM series is a line of low-power-consumption RISC chip designs
 	  licensed by ARM Ltd and targeted at embedded applications and
diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index 5cad8a6..d9b5ee5 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -108,12 +108,12 @@ endif
 
 targets       := vmlinux vmlinux.lds \
 		 piggy.$(suffix_y) piggy.$(suffix_y).o \
-		 lib1funcs.o lib1funcs.S ashldi3.o ashldi3.S \
-		 font.o font.c head.o misc.o $(OBJS)
+		 lib1funcs.o lib1funcs.S ashldi3.o ashldi3.S bswapsdi2.o \
+		 bswapsdi2.S font.o font.c head.o misc.o $(OBJS)
 
 # Make sure files are removed during clean
 extra-y       += piggy.gzip piggy.lzo piggy.lzma piggy.xzkern \
-		 lib1funcs.S ashldi3.S $(libfdt) $(libfdt_hdrs)
+		 lib1funcs.S ashldi3.S bswapsdi2.S $(libfdt) $(libfdt_hdrs)
 
 ifeq ($(CONFIG_FUNCTION_TRACER),y)
 ORIG_CFLAGS := $(KBUILD_CFLAGS)
@@ -155,6 +155,12 @@ ashldi3 = $(obj)/ashldi3.o
 $(obj)/ashldi3.S: $(srctree)/arch/$(SRCARCH)/lib/ashldi3.S
 	$(call cmd,shipped)
 
+# For __bswapsi2, __bswapdi2
+bswapsdi2 = $(obj)/bswapsdi2.o
+
+$(obj)/bswapsdi2.S: $(srctree)/arch/$(SRCARCH)/lib/bswapsdi2.S
+	$(call cmd,shipped)
+
 # We need to prevent any GOTOFF relocs being used with references
 # to symbols in the .bss section since we cannot relocate them
 # independently from the rest at run time.  This can be achieved by
@@ -176,7 +182,8 @@ if [ $(words $(ZRELADDR)) -gt 1 -a "$(CONFIG_AUTO_ZRELADDR)" = "" ]; then \
 fi
 
 $(obj)/vmlinux: $(obj)/vmlinux.lds $(obj)/$(HEAD) $(obj)/piggy.$(suffix_y).o \
-		$(addprefix $(obj)/, $(OBJS)) $(lib1funcs) $(ashldi3) FORCE
+		$(addprefix $(obj)/, $(OBJS)) $(lib1funcs) $(ashldi3) \
+		$(bswapsdi2) FORCE
 	@$(check_for_multiple_zreladdr)
 	$(call if_changed,ld)
 	@$(check_for_bad_syms)
diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c
index 60d3b73..ba578f7 100644
--- a/arch/arm/kernel/armksyms.c
+++ b/arch/arm/kernel/armksyms.c
@@ -35,6 +35,8 @@ extern void __ucmpdi2(void);
 extern void __udivsi3(void);
 extern void __umodsi3(void);
 extern void __do_div64(void);
+extern void __bswapsi2(void);
+extern void __bswapdi2(void);
 
 extern void __aeabi_idiv(void);
 extern void __aeabi_idivmod(void);
@@ -114,6 +116,8 @@ EXPORT_SYMBOL(__ucmpdi2);
 EXPORT_SYMBOL(__udivsi3);
 EXPORT_SYMBOL(__umodsi3);
 EXPORT_SYMBOL(__do_div64);
+EXPORT_SYMBOL(__bswapsi2);
+EXPORT_SYMBOL(__bswapdi2);
 
 #ifdef CONFIG_AEABI
 EXPORT_SYMBOL(__aeabi_idiv);
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index af72969..5383df7 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -13,7 +13,7 @@ lib-y		:= backtrace.o changebit.o csumipv6.o csumpartial.o   \
 		   ashldi3.o ashrdi3.o lshrdi3.o muldi3.o             \
 		   ucmpdi2.o lib1funcs.o div64.o                      \
 		   io-readsb.o io-writesb.o io-readsl.o io-writesl.o  \
-		   call_with_stack.o
+		   call_with_stack.o bswapsdi2.o
 
 mmu-y	:= clear_user.o copy_page.o getuser.o putuser.o
 
diff --git a/arch/arm/lib/bswapsdi2.S b/arch/arm/lib/bswapsdi2.S
new file mode 100644
index 0000000..2ba43a0
--- /dev/null
+++ b/arch/arm/lib/bswapsdi2.S
@@ -0,0 +1,36 @@
+#include <linux/linkage.h>
+
+#if __LINUX_ARM_ARCH__ >= 6
+ENTRY(__bswapsi2)
+	rev	r0, r0
+	bx	lr
+ENDPROC(__bswapsi2)
+
+ENTRY(__bswapdi2)
+	rev	r3, r0
+	rev	r0, r1
+	mov	r1, r3
+	bx	lr
+ENDPROC(__bswapdi2)
+#else
+ENTRY(__bswapsi2)
+	eor     r3, r0, r0, ror #16
+	mov     r3, r3, lsr #8
+	bic     r3, r3, #0xff00
+	eor     r0, r3, r0, ror #8
+	mov     pc, lr
+ENDPROC(__bswapsi2)
+
+ENTRY(__bswapdi2)
+	mov     ip, r1
+	eor     r3, ip, ip, ror #16
+	eor     r1, r0, r0, ror #16
+	mov     r1, r1, lsr #8
+	mov     r3, r3, lsr #8
+	bic     r3, r3, #0xff00
+	bic     r1, r1, #0xff00
+	eor     r1, r1, r0, ror #8
+	eor     r0, r3, ip, ror #8
+	mov     pc, lr
+ENDPROC(__bswapdi2)
+#endif
-- 
1.8.1.4