linux-kernel - Re: [PATCH v2 2/4] modpost: inform compilers that fatal() never returns

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Message-ID: <CAK7LNATDD2gC53T5n7vCUH6O6mdAm801fTWyKi9fji+5Kb+0ng@mail.gmail.com>
Date: Mon, 22 Jan 2024 22:29:32 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Aiden Leong <aiden.leong@...sd.com>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	nathan@...nel.org, ndesaulniers@...gle.com, nicolas@...sle.eu, 
	clang-built-linux <llvm@...ts.linux.dev>, 
	F���ng-ru��� S���ng <maskray@...gle.com>
Subject: Re: [PATCH v2 2/4] modpost: inform compilers that fatal() never returns

+CC: clang-built-linux list, Fangrui

On Mon, Jan 22, 2024 at 1:04 PM Aiden Leong <aiden.leong@...sd.com> wrote:
>
>
>  > The function fatal() never returns because modpost_log() calls exit(1)
>
>  > when LOG_FATAL is passed.
>  >
>  > Inform compilers of this fact so that unreachable code flow can be
>  > identified at compile time.
>  >
>  > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
>  > Reviewed-by: Nathan Chancellor <nathan@...nel.org>
>  > ---
>  >
>  > Changes in v2:
>  >   - Use noreturn attribute together with alias
>  >
>  >  scripts/mod/modpost.c | 3 +++
>  >  scripts/mod/modpost.h | 5 ++++-
>  >  2 files changed, 7 insertions(+), 1 deletion(-)
>  >
>  > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
>  > index ca0a90158f85..c13bc9095df3 100644
>  > --- a/scripts/mod/modpost.c
>  > +++ b/scripts/mod/modpost.c
>  > @@ -90,6 +90,9 @@ void modpost_log(enum loglevel loglevel, const char
> *fmt, ...)
>  >          error_occurred = true;
>  >  }
>  >
>  > +void __attribute__((alias("modpost_log")))
>
> Hi Masahiro,
> I cross-compile kernel on Apple Silicon MacBook Pro
> and every thing works well until this patch.
>
> My build command:
> make ARCH=arm CROSS_COMPILE=arm-none-eabi- \
> HOSTCFLAGS="-I/opt/homebrew/opt/openssl/include" \
> HOSTLDFLAGS="-L/opt/homebrew/opt/openssl/lib"
>
> Error message:
> scripts/mod/modpost.c:93:21: error: aliases are not supported on darwin


It is unfortunate.  Indeed, I see this message in:

clang/include/clang/Basic/DiagnosticSemaKinds.td


Is this limitation due to macOS executable (PEF),
or is it Clang-specific?

Perhaps, "brew install gcc" can be a solution?










>
> Aiden Leong
>
>  > +modpost_log_noret(enum loglevel loglevel, const char *fmt, ...);
>  > +
>  >  static inline bool strends(const char *str, const char *postfix)
>  >  {
>  >      if (strlen(str) < strlen(postfix))
>  > diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
>  > index 9fe974dc1a52..835cababf1b0 100644
>  > --- a/scripts/mod/modpost.h
>  > +++ b/scripts/mod/modpost.h
>  > @@ -200,6 +200,9 @@ enum loglevel {
>  >  void __attribute__((format(printf, 2, 3)))
>  >  modpost_log(enum loglevel loglevel, const char *fmt, ...);
>  >
>  > +void __attribute__((format(printf, 2, 3), noreturn))
>  > +modpost_log_noret(enum loglevel loglevel, const char *fmt, ...);
>  > +
>  >  /*
>  >   * warn - show the given message, then let modpost continue running,
> still
>  >   *        allowing modpost to exit successfully. This should be used
> when
>  > @@ -215,4 +218,4 @@ modpost_log(enum loglevel loglevel, const char
> *fmt, ...);
>  >   */
>  >  #define warn(fmt, args...)    modpost_log(LOG_WARN, fmt, ##args)
>  >  #define error(fmt, args...)    modpost_log(LOG_ERROR, fmt, ##args)
>  > -#define fatal(fmt, args...)    modpost_log(LOG_FATAL, fmt, ##args)
>  > +#define fatal(fmt, args...)    modpost_log_noret(LOG_FATAL, fmt, ##args)
>  > --
>  > 2.40.1



--
Best Regards
Masahiro Yamada