linux-kernel - Re: [PATCH v3 5/6] x86/ftrace: Use text

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Message-ID: <ri6d0baqxtd.fsf@suse.cz>
Date:   Thu, 23 Jan 2020 11:19:58 +0100
From:   Martin Jambor <mjambor@...e.cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Jessica Yu <jeyu@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, live-patching@...r.kernel.org,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()

Hello,

On Wed, Jan 22 2020, Josh Poimboeuf wrote:
> Global noreturns are already a pain today.  There's no way for objtool
> to know whether GCC considered a function to be noreturn,

You should be able to get a good idea with -Wsuggest-attribute=noreturn:

$ cat a.c
int __attribute__((noreturn)) my_abort (void)
{
  __builtin_abort ();
}

int foo (void)
{
  return my_abort ();
}

int bar (int flag)
{
  if (flag)
    foo ();
  return 4;
}

$ gcc -S -O2 -Wsuggest-attribute=noreturn a.c 
a.c: In function ‘foo’:
a.c:6:5: warning: function might be candidate for attribute ‘noreturn’ [-Wsuggest-attribute=noreturn]
    6 | int foo (void)
      |     ^~~

GCC 9 and newer even have -fdiagnostics-format=json if you are into that
kind of thing.

Hope this helps a little,

Martin