linux-kernel - Re: [PATCH 09/10] objtool: Drop noinstr hack for KCSAN_WEAK

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Message-ID: <CANpmjNN243_NoHOEdHvs0zDTzX5w4hjWoeo9TnQbwgfPzOWJAA@mail.gmail.com>
Date: Tue, 19 Aug 2025 12:35:37 +0200
From: Marco Elver <elver@...gle.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Arnd Bergmann <arnd@...db.de>, 
	Kees Cook <kees@...nel.org>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev, patches@...ts.linux.dev, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com
Subject: Re: [PATCH 09/10] objtool: Drop noinstr hack for KCSAN_WEAK_MEMORY

On Mon, 18 Aug 2025 at 20:58, Nathan Chancellor <nathan@...nel.org> wrote:
>
> Now that the minimum supported version of LLVM for building the kernel
> has been bumped to 15.0.0, __no_kcsan will always ensure that the thread
> sanitizer functions are not generated, so remove the check for tsan
> functions in is_profiling_func() and the always true depends and
> unnecessary select lines in KCSAN_WEAK_MEMORY.
>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Acked-by: Marco Elver <elver@...gle.com>

Good riddance.

> ---
> Cc: Josh Poimboeuf <jpoimboe@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Marco Elver <elver@...gle.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: kasan-dev@...glegroups.com
> ---
>  lib/Kconfig.kcsan     |  6 ------
>  tools/objtool/check.c | 10 ----------
>  2 files changed, 16 deletions(-)
>
> diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> index 609ddfc73de5..4ce4b0c0109c 100644
> --- a/lib/Kconfig.kcsan
> +++ b/lib/Kconfig.kcsan
> @@ -185,12 +185,6 @@ config KCSAN_WEAK_MEMORY
>         bool "Enable weak memory modeling to detect missing memory barriers"
>         default y
>         depends on KCSAN_STRICT
> -       # We can either let objtool nop __tsan_func_{entry,exit}() and builtin
> -       # atomics instrumentation in .noinstr.text, or use a compiler that can
> -       # implement __no_kcsan to really remove all instrumentation.
> -       depends on !ARCH_WANTS_NO_INSTR || HAVE_NOINSTR_HACK || \
> -                  CC_IS_GCC || CLANG_VERSION >= 140000
> -       select OBJTOOL if HAVE_NOINSTR_HACK
>         help
>           Enable support for modeling a subset of weak memory, which allows
>           detecting a subset of data races due to missing memory barriers.
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index d14f20ef1db1..efa4c060ff4e 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -2453,16 +2453,6 @@ static bool is_profiling_func(const char *name)
>         if (!strncmp(name, "__sanitizer_cov_", 16))
>                 return true;
>
> -       /*
> -        * Some compilers currently do not remove __tsan_func_entry/exit nor
> -        * __tsan_atomic_signal_fence (used for barrier instrumentation) with
> -        * the __no_sanitize_thread attribute, remove them. Once the kernel's
> -        * minimum Clang version is 14.0, this can be removed.
> -        */
> -       if (!strncmp(name, "__tsan_func_", 12) ||
> -           !strcmp(name, "__tsan_atomic_signal_fence"))
> -               return true;
> -
>         return false;
>  }
>
>
> --
> 2.50.1
>