From: Kees Cook <keescook@chromium.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Linux Next Mailing List <linux-next@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: linux-next: Tree for Mar 18 (objtool)
Date: Tue, 24 Mar 2020 11:18:07 -0700 [thread overview]
Message-ID: <202003241105.4707F983@keescook> (raw)
In-Reply-To: <20200324164433.qusyu5h7ykx3f2bu@treble>
On Tue, Mar 24, 2020 at 11:44:33AM -0500, Josh Poimboeuf wrote:
> On Fri, Mar 20, 2020 at 11:35:37AM -0700, Kees Cook wrote:
> > On Fri, Mar 20, 2020 at 09:26:13AM +0100, Peter Zijlstra wrote:
> > > On Thu, Mar 19, 2020 at 12:45:50PM -0500, Josh Poimboeuf wrote:
> > > > > On Thu, Mar 19, 2020 at 12:33:31PM -0500, Josh Poimboeuf wrote:
> > >
> > > > > > Actually I suspect it's the __builtin_unreachable() annotation which is
> > > > > > making UBSAN add the __builtin_trap()... because I don't see any double
> > > > > > UD2s for WARNs.
> > >
> > > > Actually, removing __builtin_unreachable() *does* make the extra UD2 go
> > > > away -- I forgot I had some silly debug code.
> > >
> > > LOL, check this:
> > >
> > > "Built-in Function: void __builtin_unreachable (void)
> > >
> > > If control flow reaches the point of the __builtin_unreachable, the
> > > program is undefined. It is useful in situations where the compiler
> > > cannot deduce the unreachability of the code. "
> > >
> > > Which, I bet, is what makes UBSAN insert that __builtin_trap().
> > >
> > > What a friggin mess :/
> >
> > What I'd like is to be able to specify to UBSAN what function to call
> > for the trap. I'd prefer to specify a well-defined exception handler,
> > but at present, UBSAN just inserts __builtin_trap().
> >
> > Can't objtool be told to ignore a ud2 that lacks an execution path to it?
>
> It can ignore unreachable UD2s, if we think that's the right fix.
>
> I was hoping we could find a way to get rid of the double UD2s, but I
> couldn't figure out a way to do that when I looked at it last week.
As far as I could tell, this needs patches to the UBSAN support in gcc
and clang. I have opened bugs for each:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94307
https://bugs.llvm.org/show_bug.cgi?id=45295
--
Kees Cook
next prev parent reply other threads:[~2020-03-24 18:18 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-18 11:09 linux-next: Tree for Mar 18 Stephen Rothwell
2020-03-18 16:14 ` linux-next: Tree for Mar 18 (drivers/base/power/sysfs.c) Randy Dunlap
2020-03-19 3:20 ` Stephen Rothwell
2020-03-19 14:47 ` [PATCH net-next] sysfs: fix static inline declaration of sysfs_groups_change_owner() Christian Brauner
2020-03-19 16:19 ` Randy Dunlap
2020-03-20 4:17 ` David Miller
2020-03-18 16:48 ` linux-next: Tree for Mar 18 (objtool) Randy Dunlap
2020-03-18 16:55 ` Josh Poimboeuf
2020-03-18 18:23 ` Josh Poimboeuf
2020-03-18 20:05 ` Peter Zijlstra
2020-03-19 11:12 ` Peter Zijlstra
2020-03-19 17:31 ` Josh Poimboeuf
2020-03-19 17:33 ` Josh Poimboeuf
2020-03-19 17:40 ` Josh Poimboeuf
2020-03-19 17:45 ` Josh Poimboeuf
2020-03-20 8:26 ` Peter Zijlstra
2020-03-20 18:35 ` Kees Cook
2020-03-24 16:44 ` Josh Poimboeuf
2020-03-24 18:18 ` Kees Cook [this message]
2020-03-24 22:24 ` Josh Poimboeuf
2020-03-26 5:57 ` Kees Cook
2020-03-26 16:31 ` Josh Poimboeuf
2020-03-26 18:36 ` Kees Cook
2020-03-27 3:55 ` Josh Poimboeuf
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