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From: Jakub Jelinek <jakub@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
	linux-kernel@vger.kernel.org,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	linux-toolchains@vger.kernel.org
Subject: Re: objtool warning, branch, patch, and .config (GCC bug)
Date: Thu, 26 May 2022 11:02:02 +0200	[thread overview]
Message-ID: <Yo9CCoEF7nOd6lQI@tucnak> (raw)
In-Reply-To: <20220526080849.GF6479@worktop.programming.kicks-ass.net>

On Thu, May 26, 2022 at 10:08:49AM +0200, Peter Zijlstra wrote:
> On Thu, May 26, 2022 at 10:03:13AM +0200, Peter Zijlstra wrote:
> 
> > Which is just bloody weird/broken if you ask me. What's worse, GCC-10
> > does the same. Only when I use GCC-11 do I get sensible code again:
> 
> Just to clarify, I can reproduce using:
> 
> gcc-9 (Debian 9.4.0-5) 9.4.0
> gcc-10 (Debian 10.3.0-15) 10.3.0
> 
> The good compiler is:
> 
> gcc-11 (Debian 11.3.0-1) 11.3.0

Such fallthrough into another function is typically the result
of __builtin_unreachable (), either explicit somewhere in the code,
or invoking undefined behavior somewhere and __builtin_unreachable ()
replacing the UB code.
I'd need preprocessed source + full gcc command line to tell more
(as long as it is not LTO, with LTO that isn't enough of course).

	Jakub


  reply	other threads:[~2022-05-26  9:02 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20220525173332.GA4008581@paulmck-ThinkPad-P17-Gen-1>
     [not found] ` <20220525173444.GA4010526@paulmck-ThinkPad-P17-Gen-1>
2022-05-26  8:03   ` objtool warning, branch, patch, and .config (GCC bug) Peter Zijlstra
2022-05-26  8:08     ` Peter Zijlstra
2022-05-26  9:02       ` Jakub Jelinek [this message]
     [not found]         ` <20220526094124.GN2578@worktop.programming.kicks-ass.net>
2022-05-26 11:32           ` Jakub Jelinek
2022-05-26 11:54             ` Peter Zijlstra

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