linux-kernel - Re: [PATCH] kbuild: dummy-tools: pretend we understand -fpatchable-function-entry

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Date:   Tue, 31 Oct 2023 09:09:22 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
Cc:     masahiroy@...nel.org, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        linux-kbuild@...r.kernel.org, Naveen N Rao <naveen@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH] kbuild: dummy-tools: pretend we understand
 -fpatchable-function-entry

On Mon, Oct 30, 2023 at 12:34:16PM +0100, Jiri Slaby (SUSE) wrote:
> Commit 0f71dcfb4aef (powerpc/ftrace: Add support for
> -fpatchable-function-entry) added a script to check for
> -fpatchable-function-entry compiler support. The script expects compiler
> to emit the section __patchable_function_entries and few nops after a
> function entry.
> 
> If the compiler understands and emits the above,
> CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY is set.
> 
> So teach dummy-tools' gcc about this.
> 
> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.org>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: Nathan Chancellor <nathan@...nel.org>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Nicolas Schier <nicolas@...sle.eu>
> Cc: linux-kbuild@...r.kernel.org
> Cc: Naveen N Rao <naveen@...nel.org>
> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> ---

This seems reasonable to me. I did not test it but it seems like it
should work based on my reading of gcc-check-fpatchable-function-entry.sh.

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

One minor nit, there should be quotes around the subject of 0f71dcfb4aef
in the commit message, should there need to be a v2 for some reason.

>  scripts/dummy-tools/gcc | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/scripts/dummy-tools/gcc b/scripts/dummy-tools/gcc
> index 07f6dc4c5cf6..e6c41427c02f 100755
> --- a/scripts/dummy-tools/gcc
> +++ b/scripts/dummy-tools/gcc
> @@ -91,6 +91,16 @@ if arg_contain -S "$@"; then
>  		fi
>  		exit 0
>  	fi
> +
> +	# For arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh
> +	if arg_contain -m64 "$@" && arg_contain -fpatchable-function-entry=2 "$@"; then
> +		echo "func:"
> +		echo ".section __patchable_function_entries"
> +		echo ".localentry"
> +		echo "  nop"
> +		echo "  nop"
> +		exit 0
> +	fi
>  fi
>  
>  # To set GCC_PLUGINS
> -- 
> 2.42.0
>