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From:   Martin Jambor <mjambor@suse.cz>
To:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Miroslav Benes <mbenes@suse.cz>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Jessica Yu <jeyu@kernel.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org, mhiramat@kernel.org,
        bristot@redhat.com, jbaron@akamai.com,
        torvalds@linux-foundation.org, tglx@linutronix.de,
        mingo@kernel.org, namit@vmware.com, hpa@zytor.com, luto@kernel.org,
        ard.biesheuvel@linaro.org, live-patching@vger.kernel.org,
        Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()
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References: <20191015153120.GA21580@linux-8ccs> <7e9c7dd1-809e-f130-26a3-3d3328477437@redhat.com> <20191015182705.1aeec284@gandalf.local.home> <20191016074217.GL2328@hirez.programming.kicks-ass.net> <20191021150549.bitgqifqk2tbd3aj@treble> <20200120165039.6hohicj5o52gdghu@treble> <alpine.LSU.2.21.2001210922060.6036@pobox.suse.cz> <20200121161045.dhihqibnpyrk2lsu@treble> <alpine.LSU.2.21.2001221312030.15957@pobox.suse.cz> <alpine.LSU.2.21.2001221556160.15957@pobox.suse.cz> <20200122220350.zvwyrkip5mvv6j7g@treble>
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Date:   Thu, 23 Jan 2020 11:19:58 +0100
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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