linux-kernel - Re: linux-next: Tree for Mar 18 (objtool)

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Message-ID: <20200319111236.GC20760@hirez.programming.kicks-ass.net>
Date:   Thu, 19 Mar 2020 12:12:36 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>, jakub@...hat.com,
        dvyukov@...gle.com
Subject: Re: linux-next: Tree for Mar 18 (objtool)

On Wed, Mar 18, 2020 at 09:05:42PM +0100, Peter Zijlstra wrote:
> On Wed, Mar 18, 2020 at 01:23:52PM -0500, Josh Poimboeuf wrote:

> >   545ed6816b72 ("ubsan: add trap instrumentation option")
> > 
> > Kees, any idea why that commit causes at least some BUG() statements to
> > output an extra UD2?
> 
> "Built-in Function: void __builtin_trap (void)
> 
>     This function causes the program to exit abnormally. GCC implements
>     this function by using a target-dependent mechanism (such as
>     intentionally executing an illegal instruction) or by calling abort.
>     The mechanism used may vary from release to release so you should
>     not rely on any particular implementation."
> 
> Sounds encouraging :-(

Kees, can you tell the GCC/LLVM folks that now you've used it in the
kernel we have very definite expectations of the implementation. Them
changing it is no longer an option.