linux-kernel - [PATCH v3 09/59] x86/asm: Differentiate between code and function alignment

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Date:   Thu, 15 Sep 2022 13:10:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Johannes Wikner <kwikner@...z.ch>,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
        Joao Moreira <joao.moreira@...el.com>,
        Joseph Nuzman <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v3 09/59] x86/asm: Differentiate between code and function alignment

From: Thomas Gleixner <tglx@...utronix.de>

Create SYM_F_ALIGN to differentiate alignment requirements between
SYM_CODE and SYM_FUNC.

This distinction is useful later when adding padding in front of
functions; IOW this allows following the compiler's
patchable-function-entry option.

[peterz: Changelog]
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/linkage.h |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -12,11 +12,15 @@
 #define asmlinkage CPP_ASMLINKAGE __attribute__((regparm(0)))
 #endif /* CONFIG_X86_32 */
 
-#ifdef __ASSEMBLY__
-
 #define __ALIGN		.balign CONFIG_FUNCTION_ALIGNMENT, 0x90;
 #define __ALIGN_STR	__stringify(__ALIGN)
 
+#define ASM_FUNC_ALIGN		__ALIGN_STR
+#define __FUNC_ALIGN		__ALIGN
+#define SYM_F_ALIGN		__FUNC_ALIGN
+
+#ifdef __ASSEMBLY__
+
 #if defined(CONFIG_RETHUNK) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO)
 #define RET	jmp __x86_return_thunk
 #else /* CONFIG_RETPOLINE */
@@ -43,7 +47,7 @@
 
 /* SYM_FUNC_START -- use for global functions */
 #define SYM_FUNC_START(name)				\
-	SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)	\
+	SYM_START(name, SYM_L_GLOBAL, SYM_F_ALIGN)	\
 	ENDBR
 
 /* SYM_FUNC_START_NOALIGN -- use for global functions, w/o alignment */
@@ -53,7 +57,7 @@
 
 /* SYM_FUNC_START_LOCAL -- use for local functions */
 #define SYM_FUNC_START_LOCAL(name)			\
-	SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN)	\
+	SYM_START(name, SYM_L_LOCAL, SYM_F_ALIGN)	\
 	ENDBR
 
 /* SYM_FUNC_START_LOCAL_NOALIGN -- use for local functions, w/o alignment */
@@ -63,7 +67,7 @@
 
 /* SYM_FUNC_START_WEAK -- use for weak functions */
 #define SYM_FUNC_START_WEAK(name)			\
-	SYM_START(name, SYM_L_WEAK, SYM_A_ALIGN)	\
+	SYM_START(name, SYM_L_WEAK, SYM_F_ALIGN)	\
 	ENDBR
 
 /* SYM_FUNC_START_WEAK_NOALIGN -- use for weak functions, w/o alignment */