linux-kernel - [PATCH] arm64: ftrace: Don't forbid CALL_OPS+CC_OPTIMIZE_FOR

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Date: Thu, 22 Feb 2024 22:40:29 -0800
From: Stephen Boyd <swboyd@...omium.org>
To: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>
Cc: linux-kernel@...r.kernel.org,
	patches@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	Jason Ling <jasonling@...omium.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	Mark Rutland <mark.rutland@....com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	llvm@...ts.linux.dev
Subject: [PATCH] arm64: ftrace: Don't forbid CALL_OPS+CC_OPTIMIZE_FOR_SIZE with Clang

Per commit b3f11af9b2ce ("arm64: ftrace: forbid CALL_OPS with
CC_OPTIMIZE_FOR_SIZE"), GCC is silently ignoring `-falign-functions=N`
when passed `-Os`, causing functions to be improperly aligned. This
doesn't seem to be a problem with Clang though, where enabling CALL_OPS
with CC_OPTIMIZE_FOR_SIZE doesn't spit out any warnings at boot about
misaligned patch-sites. Only forbid CALL_OPS if GCC is used and we're
optimizing for size so that CALL_OPS can be used with clang optimizing
for size.

Cc: Jason Ling <jasonling@...omium.org>
Cc: Florian Fainelli <f.fainelli@...il.com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Bill Wendling <morbo@...gle.com>
Cc: Justin Stitt <justinstitt@...gle.com>
Cc: <llvm@...ts.linux.dev>
Fixes: b3f11af9b2ce ("arm64: ftrace: forbid CALL_OPS with CC_OPTIMIZE_FOR_SIZE")
Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---
 arch/arm64/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index aa7c1d435139..6b96d75a3a3d 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -198,7 +198,7 @@ config ARM64
 		if DYNAMIC_FTRACE_WITH_ARGS && DYNAMIC_FTRACE_WITH_CALL_OPS
 	select HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS \
 		if (DYNAMIC_FTRACE_WITH_ARGS && !CFI_CLANG && \
-		    !CC_OPTIMIZE_FOR_SIZE)
+		    (CC_IS_CLANG || !CC_OPTIMIZE_FOR_SIZE))
 	select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \
 		if DYNAMIC_FTRACE_WITH_ARGS
 	select HAVE_SAMPLE_FTRACE_DIRECT

base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
-- 
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