linux-kernel - [PATCH v2] arch: enable HAS_LTO

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Message-Id: <20230717-enable-kasan-lto1-v2-1-d47bf182f5c6@gmail.com>
Date:   Tue, 18 Jul 2023 08:49:30 +0200
From:   Jakob Koschel <jkl820.git@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Jakob Koschel <jkl820.git@...il.com>
Subject: [PATCH v2] arch: enable HAS_LTO_CLANG with KASAN and KCOV

Both KASAN and KCOV had issues with LTO_CLANG if DEBUG_INFO is enabled.
With LTO inlinable function calls are required to have debug info if
they are inlined into a function that has debug info.

Starting with LLVM 17 this will be fixed ([1],[2]) and enabling LTO with
KASAN/KCOV and DEBUG_INFO doesn't cause linker errors anymore.

Link: https://github.com/llvm/llvm-project/commit/913f7e93dac67ecff47bade862ba42f27cb68ca9
Link: https://github.com/llvm/llvm-project/commit/4a8b1249306ff11f229320abdeadf0c215a00400
Reviewed-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Jakob Koschel <jkl820.git@...il.com>
---
Changes in v2:
- Added correct To:/Cc:
- Added comment about required LLVM 17 version dependency
- Link to v1: https://lore.kernel.org/r/20230717-enable-kasan-lto1-v1-1-471e706a5c4e@gmail.com
---
 arch/Kconfig | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index aff2746c8af2..d722bcfcc870 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -745,7 +745,10 @@ config HAS_LTO_CLANG
 	depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
 	depends on ARCH_SUPPORTS_LTO_CLANG
 	depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
-	depends on !KASAN || KASAN_HW_TAGS
+	# KASAN & KCOV were missing necessary debug information prior to LLVM 17
+	# which are required with LTO.
+	depends on (!KASAN || KASAN_HW_TAGS || CLANG_VERSION >= 170000) || !DEBUG_INFO
+	depends on (!KCOV || CLANG_VERSION >= 170000) || !DEBUG_INFO
 	depends on !GCOV_KERNEL
 	help
 	  The compiler and Kconfig options support building with Clang's

---
base-commit: fdf0eaf11452d72945af31804e2a1048ee1b574c
change-id: 20230717-enable-kasan-lto1-656754c76241

Best regards,
-- 
Jakob Koschel <jkl820.git@...il.com>