linux-kernel - [PATCH 3/8] arm64: Extend support for CONFIG_FUNCTION

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Message-Id: <20230109135828.879136-4-mark.rutland@arm.com>
Date:   Mon,  9 Jan 2023 13:58:23 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     catalin.marinas@....com, lenb@...nel.org,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, mhiramat@...nel.org, ndesaulniers@...gle.com,
        ojeda@...nel.org, peterz@...radead.org, rafael.j.wysocki@...el.com,
        revest@...omium.org, robert.moore@...el.com, rostedt@...dmis.org,
        will@...nel.org
Subject: [PATCH 3/8] arm64: Extend support for CONFIG_FUNCTION_ALIGNMENT

On arm64 we don't align assembly funciton in the same way as C
functions. This somewhat limits the utility of
CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B for testing.

Follow the example of x86, and align assembly functions in the same way
as C functions.

I've tested this by selecting CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B=y,
building and booting a kernel, and looking for misaligned text symbols:

Before:
  # grep ' [Tt] ' /proc/kallsyms | grep -iv '[048c]0 [Tt] ' | wc -l
  322

After:
  # grep ' [Tt] ' /proc/kallsyms | grep -iv '[048c]0 [Tt] ' | wc -l
  115

The remaining unaligned text symbols are a combination of non-function labels
in assembly and early position-independent code which is built with '-Os'.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Florent Revest <revest@...omium.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Will Deacon <will@...nel.org>
---
 arch/arm64/include/asm/linkage.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h
index 1436fa1cde24d..df18a3446ce82 100644
--- a/arch/arm64/include/asm/linkage.h
+++ b/arch/arm64/include/asm/linkage.h
@@ -5,8 +5,14 @@
 #include <asm/assembler.h>
 #endif
 
-#define __ALIGN		.align 2
-#define __ALIGN_STR	".align 2"
+#if CONFIG_FUNCTION_ALIGNMENT > 0
+#define ARM64_FUNCTION_ALIGNMENT	CONFIG_FUNCTION_ALIGNMENT
+#else
+#define ARM64_FUNCTION_ALIGNMENT	4
+#endif
+
+#define __ALIGN		.balign ARM64_FUNCTION_ALIGNMENT
+#define __ALIGN_STR	".balign " #ARM64_FUNCTION_ALIGNMENT
 
 /*
  * When using in-kernel BTI we need to ensure that PCS-conformant
-- 
2.30.2