linux-kernel - [PATCH v3 1/2] x86/asm: add _ASM_RIP() macro for x86-64 (%rip) suffix

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Message-Id: <20210910195910.2542662-3-hpa@zytor.com>
Date:   Fri, 10 Sep 2021 12:59:09 -0700
From:   "H. Peter Anvin (Intel)" <hpa@...or.com>
To:     Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>
Cc:     x86 mailing list <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin (Intel)" <hpa@...or.com>
Subject: [PATCH v3 1/2] x86/asm: add _ASM_RIP() macro for x86-64 (%rip) suffix

Add a macro _ASM_RIP() to add a (%rip) suffix on 64 bits only. This is
useful for immediate memory references where one doesn't want gcc
to possibly use a register indirection as it may in the case of an "m"
constraint.

Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
---
 arch/x86/include/asm/asm.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 3ad3da9a7d97..c5a19ccda0fe 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -6,11 +6,13 @@
 # define __ASM_FORM(x, ...)		x,## __VA_ARGS__
 # define __ASM_FORM_RAW(x, ...)		x,## __VA_ARGS__
 # define __ASM_FORM_COMMA(x, ...)	x,## __VA_ARGS__,
+# define __ASM_REGPFX			%
 #else
 #include <linux/stringify.h>
 # define __ASM_FORM(x, ...)		" " __stringify(x,##__VA_ARGS__) " "
 # define __ASM_FORM_RAW(x, ...)		    __stringify(x,##__VA_ARGS__)
 # define __ASM_FORM_COMMA(x, ...)	" " __stringify(x,##__VA_ARGS__) ","
+# define __ASM_REGPFX			%%
 #endif
 
 #define _ASM_BYTES(x, ...)	__ASM_FORM(.byte x,##__VA_ARGS__ ;)
@@ -49,6 +51,9 @@
 #define _ASM_SI		__ASM_REG(si)
 #define _ASM_DI		__ASM_REG(di)
 
+/* Adds a (%rip) suffix on 64 bits only; for immediate memory references */
+#define _ASM_RIP(x)	__ASM_SEL_RAW(x, x (__ASM_REGPFX rip))
+
 #ifndef __x86_64__
 /* 32 bit */
 
-- 
2.31.1