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@google.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)
+		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

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@google.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
>

On Tue, Jan 14, 2025 at 10:24:29AM -0700, Nathan Chancellor wrote:
> 
> 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/

Yeah, makes sense.  I'll add this:

From: Josh Poimboeuf <jpoimboe@kernel.org>
Subject: [PATCH] objtool: Change "warning:" to "error:" for CONFIG_OBJTOOL_WERROR

This matches GCC's behavior and makes it more obvious why the build
failed.

Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/include/objtool/warn.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/include/objtool/warn.h b/tools/objtool/include/objtool/warn.h
index ac04d3fe4dd9..78f602b5daed 100644
--- a/tools/objtool/include/objtool/warn.h
+++ b/tools/objtool/include/objtool/warn.h
@@ -43,8 +43,10 @@ static inline char *offstr(struct section *sec, unsigned long offset)
 
 #define WARN(format, ...)				\
 	fprintf(stderr,					\
-		"%s: warning: objtool: " format "\n",	\
-		objname, ##__VA_ARGS__)
+		"%s: %s: objtool: " format "\n",	\
+		objname,				\
+		opts.werror ? "error" : "warning",	\
+		##__VA_ARGS__)
 
 #define WARN_FUNC(format, sec, offset, ...)		\
 ({							\
-- 
2.47.1