linux-kernel - [PATCH] kcsan: select CONFIG

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Date:   Wed, 15 Feb 2023 10:14:48 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH] kcsan: select CONFIG_CONSTRUCTORS

From: Arnd Bergmann <arnd@...db.de>

Building a kcsan enabled kernel for x86_64 with gcc-11 results in a lot
of build warnings or errors without CONFIG_CONSTRUCTORS:

x86_64-linux-ld: error: unplaced orphan section `.ctors.65436' from `arch/x86/lib/copy_mc.o'
x86_64-linux-ld: error: unplaced orphan section `.ctors.65436' from `arch/x86/lib/cpu.o'
x86_64-linux-ld: error: unplaced orphan section `.ctors.65436' from `arch/x86/lib/csum-partial_64.o'
x86_64-linux-ld: error: unplaced orphan section `.ctors.65436' from `arch/x86/lib/csum-wrappers_64.o'
x86_64-linux-ld: error: unplaced orphan section `.ctors.65436' from `arch/x86/lib/insn-eval.o'
x86_64-linux-ld: error: unplaced orphan section `.ctors.65436' from `arch/x86/lib/insn.o'
x86_64-linux-ld: error: unplaced orphan section `.ctors.65436' from `arch/x86/lib/misc.o'

The same thing has been reported for mips64. I can't reproduce it for
any other compiler version, so I don't know if constructors are always
required here or if this is a gcc-11 specific implementation detail.

I see no harm in always enabling constructors here, and this reliably
fixes the build warnings for me.

Link: https://lore.kernel.org/lkml/202204181801.r3MMkwJv-lkp@intel.com/T/
Cc: Kees Cook <keescook@...omium.org>
See-also: 3e6631485fae ("vmlinux.lds.h: Keep .ctors.* with .ctors")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 lib/Kconfig.kcsan | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
index 4dedd61e5192..609ddfc73de5 100644
--- a/lib/Kconfig.kcsan
+++ b/lib/Kconfig.kcsan
@@ -14,6 +14,7 @@ menuconfig KCSAN
 	bool "KCSAN: dynamic data race detector"
 	depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER
 	depends on DEBUG_KERNEL && !KASAN
+	select CONSTRUCTORS
 	select STACKTRACE
 	help
 	  The Kernel Concurrency Sanitizer (KCSAN) is a dynamic
-- 
2.39.1