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From: Nick Desaulniers <ndesaulniers@google.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>, Marco Elver <elver@google.com>
Cc: Borislav Petkov <bp@alien8.de>, Rong Chen <rong.a.chen@intel.com>,
	kernel test robot <lkp@intel.com>,
	"Li, Philip" <philip.li@intel.com>, x86-ml <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e
Date: Tue, 15 Sep 2020 15:34:39 -0700	[thread overview]
Message-ID: <CAKwvOdmptEpi8fiOyWUo=AiZJiX+Z+VHJOM2buLPrWsMTwLnyw@mail.gmail.com> (raw)
In-Reply-To: <20200915210231.ysaibtkeibdm4zps@treble>

On Tue, Sep 15, 2020 at 2:02 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> panic() is noreturn, so the compiler is enforcing the fact that it
> doesn't return, by trapping if it does return.
>
> I seem to remember that's caused by CONFIG_UBSAN_TRAP.

Indeed, if I remove CONFIG_UBSAN_TRAP from the 0day report's
randconfig, these unreachable instruction warnings all go away.

So what's the right way to fix this?

CONFIG_UBSAN_TRAP enables -fsanitize-undefined-trap-on-error  (not
sure why that's wrapped in cc-option; it shouldn't be selectable via
Kconfig if unsupported by the toolchain).

Should clang not be emitting `ud2` trapping instructions for this flag
for no-return functions?

or

Should objtool be made aware of the config option and then not check
traps after no-returns?

I suspect the latter, but I'm not sure how feasible it is to
implement.  Josh, Marco, do you have thoughts on the above?
-- 
Thanks,
~Nick Desaulniers

  parent reply	other threads:[~2020-09-15 22:40 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-15 13:42 [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e kernel test robot
2020-09-15 13:55 ` Borislav Petkov
2020-09-15 14:18   ` Rong Chen
2020-09-15 14:41     ` Borislav Petkov
2020-09-15 16:05     ` Borislav Petkov
2020-09-15 17:02       ` Josh Poimboeuf
2020-09-15 17:21         ` Borislav Petkov
2020-09-15 17:34           ` Borislav Petkov
2020-09-15 17:41             ` Nick Desaulniers
2020-09-15 18:01               ` Borislav Petkov
2020-09-15 18:04                 ` Nick Desaulniers
2020-09-15 17:40           ` Nick Desaulniers
2020-09-15 18:09             ` Marco Elver
2020-09-16  8:30               ` peterz
2020-09-16  8:46                 ` Marco Elver
2020-09-16  9:06                   ` peterz
2020-09-16  9:33                     ` Marco Elver
2020-09-16 18:22                   ` Nick Desaulniers
2020-09-16 18:51                     ` Marco Elver
2020-09-17  4:11                       ` Fangrui Song
     [not found]                       ` <333D40A0-4550-4309-9693-1ABA4AC75399@arm.com>
2020-09-17 11:04                         ` Mark Rutland
2020-09-17 11:16                           ` Daniel Kiss
2020-09-17 18:39                     ` Josh Poimboeuf
2020-09-15 17:44         ` Nick Desaulniers
2020-09-15 20:12         ` Nick Desaulniers
2020-09-15 20:49           ` Borislav Petkov
2020-09-15 21:02             ` Josh Poimboeuf
2020-09-15 21:14               ` Borislav Petkov
2020-09-15 22:34               ` Nick Desaulniers [this message]
2020-09-16  7:03                 ` Ilie Halip
2020-09-16  8:59                 ` Marco Elver
2020-09-21 16:51                 ` [tip: objtool/core] objtool: Ignore unreachable trap after call to noreturn functions tip-bot2 for Ilie Halip
2020-09-15 21:50             ` [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e Arvind Sankar
2020-09-15 21:59               ` Nick Desaulniers
2020-09-15 22:44                 ` Arvind Sankar
2020-09-16 11:34               ` Borislav Petkov
2020-09-16 18:28                 ` Nick Desaulniers
2020-09-16 18:48                   ` Borislav Petkov
2020-09-15 21:13           ` Nick Desaulniers
2020-09-15 21:28             ` Josh Poimboeuf
2020-09-15 23:35               ` Marco Elver

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