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* [PATCH 00/10] x86: use gcc 6+ asm flag output feature
@ 2016-06-07 23:30 H. Peter Anvin
  2016-06-07 23:31 ` [PATCH 01/10] x86, bitops: remove use of "sbb" to return CF H. Peter Anvin
                   ` (11 more replies)
  0 siblings, 12 replies; 43+ messages in thread
From: H. Peter Anvin @ 2016-06-07 23:30 UTC (permalink / raw)
  To: Ingo Molnar, Thomas Gleixner, H. Peter Anvin, Linux Kernel Mailing List
  Cc: Peter Zijlstra, Andy Lutomirski, Borislav Petkov

From: "H. Peter Anvin" <hpa@zytor.com>

gcc 6+ has the ability to let flags (actually, conditions, which are
specific combinations of flags) to be used directly as asm() outputs.
The syntax for that is "=@cc<cc>" where <cc> is the same set of
letters that would be used in a j<cc> or set<cc> instruction
(e.g. "=@ccz" to test the ZF flag.)

This patchset by itself reduces the size of the x86-64 kernel by
0.12%, from a baseline of 4.7-rc2 built with gcc 6.1 (first line is
with the patchset, the second one is without):

     text       data       bss        dec       hex filename
     
 68245656   41004339  20533248  129783243   7bc55cb o.i386-allconfig/vmlinux
 68355716   41008499  20533248  129897463   7be13f7 o.i386-allconfig/vmlinux

127384005  129742359  38150144  295276508  11998fdc o.x86_64-allconfig/vmlinux
127538765  129742295  38150144  295431204  119bec24 o.x86_64-allconfig/vmlinux

^ permalink raw reply	[flat|nested] 43+ messages in thread
* [PATCH v2 05/10] x86, asm: change GEN_*_RMWcc() to use CC_SET()/CC_OUT()
@ 2016-06-08 19:38 H. Peter Anvin
  2016-06-08 19:47 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
  0 siblings, 1 reply; 43+ messages in thread
From: H. Peter Anvin @ 2016-06-08 19:38 UTC (permalink / raw)
  To: Ingo Molnar, Thomas Gleixner, H. Peter Anvin, Linux Kernel Mailing List
  Cc: Andy Lutomirski, Borislav Petkov

From: "H. Peter Anvin" <hpa@zytor.com>

Change the GEN_*_RMWcc() macros to use the CC_SET()/CC_OUT() macros
defined in <asm/asm.h>, and disable the use of asm goto if
__GCC_ASM_FLAG_OUTPUTS__ is enabled.  This allows gcc to receive the
flags output directly in gcc 6+.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/include/asm/rmwcc.h | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/rmwcc.h b/arch/x86/include/asm/rmwcc.h
index e3264c4..661dd30 100644
--- a/arch/x86/include/asm/rmwcc.h
+++ b/arch/x86/include/asm/rmwcc.h
@@ -1,7 +1,9 @@
 #ifndef _ASM_X86_RMWcc
 #define _ASM_X86_RMWcc
 
-#ifdef CC_HAVE_ASM_GOTO
+#if !defined(__GCC_ASM_FLAG_OUTPUTS__) && defined(CC_HAVE_ASM_GOTO)
+
+/* Use asm goto */
 
 #define __GEN_RMWcc(fullop, var, cc, ...)				\
 do {									\
@@ -19,13 +21,15 @@ cc_label:								\
 #define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
 	__GEN_RMWcc(op " %1, " arg0, var, cc, vcon (val))
 
-#else /* !CC_HAVE_ASM_GOTO */
+#else /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CC_HAVE_ASM_GOTO) */
+
+/* Use flags output or a set instruction */
 
 #define __GEN_RMWcc(fullop, var, cc, ...)				\
 do {									\
 	bool c;								\
-	asm volatile (fullop "; set" #cc " %1"				\
-			: "+m" (var), "=qm" (c)				\
+	asm volatile (fullop ";" CC_SET(cc)				\
+			: "+m" (var), CC_OUT(cc) (c)			\
 			: __VA_ARGS__ : "memory");			\
 	return c;							\
 } while (0)
@@ -36,6 +40,6 @@ do {									\
 #define GEN_BINARY_RMWcc(op, var, vcon, val, arg0, cc)			\
 	__GEN_RMWcc(op " %2, " arg0, var, cc, vcon (val))
 
-#endif /* CC_HAVE_ASM_GOTO */
+#endif /* defined(__GCC_ASM_FLAG_OUTPUTS__) || !defined(CC_HAVE_ASM_GOTO) */
 
 #endif /* _ASM_X86_RMWcc */
-- 
2.7.3.0.11.gd79db92

^ permalink raw reply related	[flat|nested] 43+ messages in thread

end of thread, other threads:[~2016-06-08 19:48 UTC | newest]

Thread overview: 43+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-06-07 23:30 [PATCH 00/10] x86: use gcc 6+ asm flag output feature H. Peter Anvin
2016-06-07 23:31 ` [PATCH 01/10] x86, bitops: remove use of "sbb" to return CF H. Peter Anvin
2016-06-07 23:39   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 02/10] x86, asm: use bool for bitops and other assembly outputs H. Peter Anvin
2016-06-07 23:40   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08  7:49   ` [PATCH 02/10] " Peter Zijlstra
2016-06-08  8:28     ` Ingo Molnar
2016-06-08  8:33       ` Ingo Molnar
2016-06-08  8:55         ` H. Peter Anvin
2016-06-08  9:01           ` Ingo Molnar
2016-06-08  9:12             ` H. Peter Anvin
2016-06-08  9:20               ` Ingo Molnar
2016-06-08  9:31                 ` H. Peter Anvin
2016-06-08  9:39                   ` Peter Zijlstra
2016-06-08  9:43                     ` H. Peter Anvin
2016-06-08  9:40                 ` H. Peter Anvin
2016-06-08  8:58       ` H. Peter Anvin
2016-06-08  9:06         ` Ingo Molnar
2016-06-07 23:31 ` [PATCH 03/10] x86, asm: change the GEN_*_RMWcc() macros to not quote the condition H. Peter Anvin
2016-06-07 23:40   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 04/10] x86, asm: define CC_SET() and CC_OUT() macros H. Peter Anvin
2016-06-07 23:40   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08  5:09   ` [PATCH 04/10] " Andy Lutomirski
2016-06-08 19:29     ` H. Peter Anvin
2016-06-08 19:34       ` H. Peter Anvin
2016-06-08 19:35         ` Borislav Petkov
2016-06-07 23:31 ` [PATCH 05/10] x86, asm: change GEN_*_RMWcc() to use CC_SET()/CC_OUT() H. Peter Anvin
2016-06-07 23:41   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 06/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/bitops.h> H. Peter Anvin
2016-06-07 23:41   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 07/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/percpu.h> H. Peter Anvin
2016-06-07 23:42   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 08/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/rwsem.h> H. Peter Anvin
2016-06-07 23:42   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 09/10] x86, asm: Use CC_SET()/CC_OUT() and static_cpu_has() in archrandom.h H. Peter Anvin
2016-06-07 23:42   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08  5:12   ` [PATCH 09/10] " Andy Lutomirski
2016-06-07 23:31 ` [PATCH 10/10] x86, asm, boot: Use CC_SET()/CC_OUT() in arch/x86/boot/boot.h H. Peter Anvin
2016-06-07 23:43   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08  8:00 ` [PATCH 00/10] x86: use gcc 6+ asm flag output feature Peter Zijlstra
2016-06-08  8:56   ` H. Peter Anvin
2016-06-08  8:26 ` Ingo Molnar
2016-06-08 19:38 [PATCH v2 05/10] x86, asm: change GEN_*_RMWcc() to use CC_SET()/CC_OUT() H. Peter Anvin
2016-06-08 19:47 ` [tip:x86/asm] " tip-bot for H. Peter Anvin

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