linux-kernel - [PATCH v3 10/12] linux/linkage: add ASM() macro to reduce duplication between C/ASM code

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Date:   Tue, 18 Dec 2018 01:03:25 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     Richard Biener <rguenther@...e.de>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juergen Gross <jgross@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 10/12] linux/linkage: add ASM() macro to reduce duplication between C/ASM code

We often duplicate similar assembly code to use it from .c and .S files.
The difference is mostly the presence of double quotes.

So, here is a new macro ASM().
(We have similar approach for __ASM_FORM(), etc.)

The usage is like this:

    #define MY_CODE              \
    ASM(    .section ".text"    )\
    ASM(    movl $1, %eax       )

In C context, the preprocessor expands it into:

  ".section \".text\"" "\n\t" "movl $1, %eax" "\n\t"

This is perfect for the use from the inline asm(...) in .c files.

In assembly context, the preprocessor expands it into:

  .section ".text" ; movl $1, %eax ;

This is fine for the use in .S files.

I used double-expansion like __stringify() so that we can use
macros in ASM(...).

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

 include/linux/linkage.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/linkage.h b/include/linux/linkage.h
index 7c47b1a..80faeae 100644
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h
@@ -12,6 +12,14 @@
 #define ASM_NL		 ;
 #endif
 
+#ifdef __ASSEMBLY__
+#define _ASM(x...)	x ASM_NL
+#else
+#define _ASM(x...)	#x __stringify(\n\t)
+#endif
+/* Doing two levels allows macros to be used in ASM(...) */
+#define ASM(x...)	_ASM(x)
+
 #ifdef __cplusplus
 #define CPP_ASMLINKAGE extern "C"
 #else
-- 
2.7.4