linux-kernel - Re: [PATCH 1/1] Makefile: Pass -warn-stack-size only on LLD

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Message-ID: <202106141448.A0BD79129@keescook>
Date:   Mon, 14 Jun 2021 14:49:48 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Tor Vic <torvic9@...lbox.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        masahiroy@...nel.org, Nathan Chancellor <nathan@...nel.org>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 1/1] Makefile: Pass -warn-stack-size only on LLD < 13.0.0

On Sun, Jun 13, 2021 at 01:07:49PM +0000, Tor Vic wrote:
> Since LLVM commit fc018eb, the '-warn-stack-size' flag has been dropped
> [1], leading to the following error message when building with Clang-13
> and LLD-13:
> 
>     ld.lld: error: -plugin-opt=-: ld.lld: Unknown command line argument
>     '-warn-stack-size=2048'.  Try: 'ld.lld --help'
>     ld.lld: Did you mean '--asan-stack=2048'?
> 
> In the same way as with commit 2398ce80152a ("x86, lto: Pass
> -stack-alignment only on LLD < 13.0.0") , make '-warn-stack-size'
> conditional on LLD < 13.0.0.
> 
> [1] https://reviews.llvm.org/D103928

Is there a way Clang can just warn instead of breaking the kernel build
when it moves these kinds of options around? That would make things must
less disruptive to the CI, etc. :)

-Kees

> Fixes: 24845dcb170e ("Makefile: LTO: have linker check -Wframe-larger-than")
> Cc: stable@...r.kernel.org
> Link: https://github.com/ClangBuiltLinux/linux/issues/1377
> Signed-off-by: Tor Vic <torvic9@...lbox.org>
> ---
>  Makefile | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index 144d4f8b7eb3..51a1b6b2c2ab 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -929,11 +929,14 @@ CC_FLAGS_LTO	+= -fvisibility=hidden
>  # Limit inlining across translation units to reduce binary size
>  KBUILD_LDFLAGS += -mllvm -import-instr-limit=5
> 
> -# Check for frame size exceeding threshold during prolog/epilog insertion.
> +# Check for frame size exceeding threshold during prolog/epilog insertion
> +# when using lld < 13.0.0.
>  ifneq ($(CONFIG_FRAME_WARN),0)
> +ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 130000; echo $$?),0)
>  KBUILD_LDFLAGS	+= -plugin-opt=-warn-stack-size=$(CONFIG_FRAME_WARN)
>  endif
>  endif
> +endif
> 
>  ifdef CONFIG_LTO
>  KBUILD_CFLAGS	+= -fno-lto $(CC_FLAGS_LTO)
> -- 
> 2.32.0

-- 
Kees Cook