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* [PATCH v2 00/10] x86: use gcc 6+ asm flag output feature
@ 2016-06-08 19:38 H. Peter Anvin
  2016-06-08 19:38 ` [PATCH v2 01/10] x86, bitops: remove use of "sbb" to return CF H. Peter Anvin
                   ` (10 more replies)
  0 siblings, 11 replies; 24+ 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>

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

v2: fix a conflict between <linux/random.h> and <asm/archrandom.h>
    discovered by Ingo Molnar.  There are a few places in x86-specific
    code where we need all of <arch/archrandom.h> even when
    xCONFIG_ARCH_RANDOM is disabled, so <linux/random.h> does not
    suffice.  Only the <asm/archrandom.h> patch has been changed;
    since it is a little bit different from the others I have moved it
    to the end.

^ permalink raw reply	[flat|nested] 24+ messages in thread
* [PATCH 09/10] x86, asm: Use CC_SET()/CC_OUT() and static_cpu_has() in archrandom.h
@ 2016-06-07 23:31 H. Peter Anvin
  2016-06-07 23:42 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
  0 siblings, 1 reply; 24+ messages in thread
From: H. Peter Anvin @ 2016-06-07 23:31 UTC (permalink / raw)
  To: Ingo Molnar, Thomas Gleixner, H. Peter Anvin,
	Linux Kernel Mailing List
  Cc: Peter Zijlstra, Andy Lutomirski, Borislav Petkov, H. Peter Anvin

Use CC_SET()/CC_OUT() and static_cpu_has().  This produces code good
enough to eliminate ad hoc use of alternatives in <asm/archrandom.h>,
greatly simplifying the code.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---
 arch/x86/include/asm/archrandom.h | 113 ++++++++++++++++----------------------
 1 file changed, 47 insertions(+), 66 deletions(-)

diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h
index ab6f599..654da36 100644
--- a/arch/x86/include/asm/archrandom.h
+++ b/arch/x86/include/asm/archrandom.h
@@ -40,96 +40,77 @@
 # define RDSEED_LONG	RDSEED_INT
 #endif
 
-#ifdef CONFIG_ARCH_RANDOM
+/* Unconditional execution of RDRAND and RDSEED */
 
-/* Instead of arch_get_random_long() when alternatives haven't run. */
 static inline bool rdrand_long(unsigned long *v)
 {
-	int ok;
-	asm volatile("1: " RDRAND_LONG "\n\t"
-		     "jc 2f\n\t"
-		     "decl %0\n\t"
-		     "jnz 1b\n\t"
-		     "2:"
-		     : "=r" (ok), "=a" (*v)
-		     : "0" (RDRAND_RETRY_LOOPS));
-	return !!ok;
+	bool ok;
+	unsigned int retry = RDRAND_RETRY_LOOPS;
+	do {
+		asm volatile(RDRAND_LONG "\n\t"
+			     CC_SET(c)
+			     : CC_OUT(c) (ok), "=a" (*v));
+		if (ok)
+			return true;
+	} while (--retry);
+	return false;
+}
+
+static inline bool rdrand_int(unsigned int *v)
+{
+	bool ok;
+	unsigned int retry = RDRAND_RETRY_LOOPS;
+	do {
+		asm volatile(RDRAND_INT "\n\t"
+			     CC_SET(c)
+			     : CC_OUT(c) (ok), "=a" (*v));
+		if (ok)
+			return true;
+	} while (--retry);
+	return false;
 }
 
-/* A single attempt at RDSEED */
 static inline bool rdseed_long(unsigned long *v)
 {
 	bool ok;
 	asm volatile(RDSEED_LONG "\n\t"
-		     "setc %0"
-		     : "=qm" (ok), "=a" (*v));
+		     CC_SET(c)
+		     : CC_OUT(c) (ok), "=a" (*v));
 	return ok;
 }
 
-#define GET_RANDOM(name, type, rdrand, nop)			\
-static inline bool name(type *v)				\
-{								\
-	int ok;							\
-	alternative_io("movl $0, %0\n\t"			\
-		       nop,					\
-		       "\n1: " rdrand "\n\t"			\
-		       "jc 2f\n\t"				\
-		       "decl %0\n\t"                            \
-		       "jnz 1b\n\t"                             \
-		       "2:",                                    \
-		       X86_FEATURE_RDRAND,                      \
-		       ASM_OUTPUT2("=r" (ok), "=a" (*v)),       \
-		       "0" (RDRAND_RETRY_LOOPS));		\
-	return !!ok;						\
-}
-
-#define GET_SEED(name, type, rdseed, nop)			\
-static inline bool name(type *v)				\
-{								\
-	bool ok;						\
-	alternative_io("movb $0, %0\n\t"			\
-		       nop,					\
-		       rdseed "\n\t"				\
-		       "setc %0",				\
-		       X86_FEATURE_RDSEED,                      \
-		       ASM_OUTPUT2("=q" (ok), "=a" (*v)));	\
-	return ok;						\
+static inline bool rdseed_int(unsigned int *v)
+{
+	bool ok;
+	asm volatile(RDSEED_INT "\n\t"
+		     CC_SET(c)
+		     : CC_OUT(c) (ok), "=a" (*v));
+	return ok;
 }
 
-#ifdef CONFIG_X86_64
-
-GET_RANDOM(arch_get_random_long, unsigned long, RDRAND_LONG, ASM_NOP5);
-GET_RANDOM(arch_get_random_int, unsigned int, RDRAND_INT, ASM_NOP4);
-
-GET_SEED(arch_get_random_seed_long, unsigned long, RDSEED_LONG, ASM_NOP5);
-GET_SEED(arch_get_random_seed_int, unsigned int, RDSEED_INT, ASM_NOP4);
-
-#else
-
-GET_RANDOM(arch_get_random_long, unsigned long, RDRAND_LONG, ASM_NOP3);
-GET_RANDOM(arch_get_random_int, unsigned int, RDRAND_INT, ASM_NOP3);
-
-GET_SEED(arch_get_random_seed_long, unsigned long, RDSEED_LONG, ASM_NOP4);
-GET_SEED(arch_get_random_seed_int, unsigned int, RDSEED_INT, ASM_NOP4);
-
-#endif /* CONFIG_X86_64 */
-
+/* Conditional execution based on CPU type */
 #define arch_has_random()	static_cpu_has(X86_FEATURE_RDRAND)
 #define arch_has_random_seed()	static_cpu_has(X86_FEATURE_RDSEED)
 
-#else
+static inline bool arch_get_random_long(unsigned long *v)
+{
+	return arch_has_random() ? rdrand_long(v) : false;
+}
 
-static inline bool rdrand_long(unsigned long *v)
+static inline bool arch_get_random_int(unsigned int *v)
 {
-	return 0;
+	return arch_has_random() ? rdrand_int(v) : false;
 }
 
-static inline bool rdseed_long(unsigned long *v)
+static inline bool arch_get_random_seed_long(unsigned long *v)
 {
-	return 0;
+	return arch_has_random_seed() ? rdseed_long(v) : false;
 }
 
-#endif  /* CONFIG_ARCH_RANDOM */
+static inline bool arch_get_random_seed_int(unsigned int *v)
+{
+	return arch_has_random_seed() ? rdseed_int(v) : false;
+}
 
 extern void x86_init_rdrand(struct cpuinfo_x86 *c);
 
-- 
2.7.3.0.11.gd79db92

^ permalink raw reply related	[flat|nested] 24+ messages in thread
end of thread, other threads:[~2016-06-09 15:49 UTC | newest]

Thread overview: 24+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2016-06-08 19:38 [PATCH v2 00/10] x86: use gcc 6+ asm flag output feature H. Peter Anvin
2016-06-08 19:38 ` [PATCH v2 01/10] x86, bitops: remove use of "sbb" to return CF H. Peter Anvin
2016-06-08 19:45   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 19:38 ` [PATCH v2 02/10] x86, asm: use bool for bitops and other assembly outputs H. Peter Anvin
2016-06-08 19:46   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 19:38 ` [PATCH v2 03/10] x86, asm: change the GEN_*_RMWcc() macros to not quote the condition H. Peter Anvin
2016-06-08 19:46   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 19:38 ` [PATCH v2 04/10] x86, asm: define CC_SET() and CC_OUT() macros H. Peter Anvin
2016-06-08 19:47   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
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
2016-06-08 19:38 ` [PATCH v2 06/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/bitops.h> H. Peter Anvin
2016-06-08 19:48   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 19:38 ` [PATCH v2 07/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/percpu.h> H. Peter Anvin
2016-06-08 19:48   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 19:38 ` [PATCH v2 08/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/rwsem.h> H. Peter Anvin
2016-06-08 19:49   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 19:38 ` [PATCH v2 09/10] x86, asm, boot: Use CC_SET()/CC_OUT() in arch/x86/boot/boot.h H. Peter Anvin
2016-06-08 19:49   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 19:38 ` [PATCH v2 10/10] x86, asm: Use CC_SET()/CC_OUT() and static_cpu_has() in archrandom.h H. Peter Anvin
2016-06-08 19:49   ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-09 15:49   ` [PATCH v2 10/10] " Borislav Petkov
2016-06-08 21:30 ` [PATCH v2 00/10] x86: use gcc 6+ asm flag output feature H. Peter Anvin
  -- strict thread matches above, loose matches on Subject: below --
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

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