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

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Message-ID: <20200320082613.GA20696@hirez.programming.kicks-ass.net>
Date:   Fri, 20 Mar 2020 09:26:13 +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>
Subject: Re: linux-next: Tree for Mar 18 (objtool)

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 :/