linux-kernel - Re: [PATCH v3 1/2] objtool: Add --Werror

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Message-ID: <20250114172429.GA246689@ax162>
Date: Tue, 14 Jan 2025 10:24:29 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Brendan Jackman <jackmanb@...gle.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>, linux-kernel@...r.kernel.org,
	linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v3 1/2] objtool: Add --Werror

On Mon, Jan 13, 2025 at 02:05:15PM +0000, Brendan Jackman wrote:
> At present objtool only prints to the terminal when observing "fatal
> warnings". This option lets you have it produce an error instead.
> 
> The use case for this is noinstr validation; so far I've never seen any
> false warnings here, but it quite often detects real bugs. It would
> be useful for the build to fail when I have those bugs.
> 
> Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
> ---
>  tools/objtool/builtin-check.c           | 6 ++++++
>  tools/objtool/check.c                   | 7 ++-----
>  tools/objtool/include/objtool/builtin.h | 1 +
>  3 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
> index 387d56a7f5fb8da8435d0a3f5c05eeee66932c9b..0b28082df90710ff7127327deb857c0548f378c7 100644
> --- a/tools/objtool/builtin-check.c
> +++ b/tools/objtool/builtin-check.c
> @@ -94,6 +94,12 @@ static const struct option check_options[] = {
>  	OPT_BOOLEAN(0, "sec-address", &opts.sec_address, "print section addresses in warnings"),
>  	OPT_BOOLEAN(0, "stats", &opts.stats, "print statistics"),
>  	OPT_BOOLEAN('v', "verbose", &opts.verbose, "verbose warnings"),
> +	/*
> +	 *  For now, don't fail the kernel build on fatal warnings by default.
> +	 *  These errors are still fairly common due to the growing matrix of
> +	 *  supported toolchains and their recent pace of change.
> +	 */
> +	OPT_BOOLEAN(0, "Werror", &opts.werror, "fail on fatal warnings"),
>  
>  	OPT_END(),
>  };
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 76060da755b5c51cda3a669d8245d7d004e25f22..e44135293eb45f908e00359d84d954cfeddd266f 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -4944,10 +4944,7 @@ int check(struct objtool_file *file)
>  	}
>  
>  out:
> -	/*
> -	 *  For now, don't fail the kernel build on fatal warnings.  These
> -	 *  errors are still fairly common due to the growing matrix of
> -	 *  supported toolchains and their recent pace of change.
> -	 */
> +	if (opts.werror && warnings)

It might be a good idea to print a message here about why the build is
failing, in lieu of turning all "objtool: warning:" messages into
"objtool: error:" messages ala -Werror for C compilers, which does not
seem simple on quick glance. Otherwise, I am not entirely sure it will
be obvious to people why a build like allmodconfig may start failing if
this configuration gets turned on.

https://lore.kernel.org/Z4X8j%2FqJj7ib0vkh@rli9-mobl/

> +		return 1;
>  	return 0;
>  }
> diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
> index fcca6662c8b4b5e0048e54fada8694cc2e6ebc34..97d668010efadfa05bb6e25e1967a7d72bf77815 100644
> --- a/tools/objtool/include/objtool/builtin.h
> +++ b/tools/objtool/include/objtool/builtin.h
> @@ -38,6 +38,7 @@ struct opts {
>  	bool sec_address;
>  	bool stats;
>  	bool verbose;
> +	bool werror;
>  };
>  
>  extern struct opts opts;
> 
> -- 
> 2.47.1.613.gc27f4b7a9f-goog
>