linux-kernel - [PATCH v2 04/10] x86, asm: define CC_SET() and CC

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Date:	Wed,  8 Jun 2016 12:38:40 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>
Subject: [PATCH v2 04/10] x86, asm: define CC_SET() and CC_OUT() macros

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

The CC_SET() and CC_OUT() macros can be used together to take
advantage of the new __GCC_ASM_FLAG_OUTPUTS__ feature in gcc 6+ while
remaining backwards compatible.  CC_SET() generates a SET instruction
on older compilers; CC_OUT() makes sure the output is received in the
correct variable.

Signed-off-by: H. Peter Anvin <hpa@...or.com>
Reviewed-by: Andy Lutomirski <luto@...nel.org>
Reviewed-by: Borislav Petkov <bp@...e.de>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/asm.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index f5063b6..7acb51c 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -42,6 +42,18 @@
 #define _ASM_SI		__ASM_REG(si)
 #define _ASM_DI		__ASM_REG(di)
 
+/*
+ * Macros to generate condition code outputs from inline assembly,
+ * The output operand must be type "bool".
+ */
+#ifdef __GCC_ASM_FLAG_OUTPUTS__
+# define CC_SET(c) "\n\t/* output condition code " #c "*/\n"
+# define CC_OUT(c) "=@cc" #c
+#else
+# define CC_SET(c) "\n\tset" #c " %[_cc_" #c "]\n"
+# define CC_OUT(c) [_cc_ ## c] "=qm"
+#endif
+
 /* Exception table entry */
 #ifdef __ASSEMBLY__
 # define _ASM_EXTABLE_HANDLE(from, to, handler)			\
-- 
2.7.3.0.11.gd79db92