linux-kernel - Re: [PATCH 2/2] x86/unwind: Make CONFIG_UNWINDER

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Date:   Tue, 20 Mar 2018 12:39:57 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, peterz@...radead.org, hpa@...or.com,
        tglx@...utronix.de
Subject: Re: [PATCH 2/2] x86/unwind: Make CONFIG_UNWINDER_ORC=y the default
 in kconfig for 64-bit

El Mon, Mar 19, 2018 at 09:28:03PM -0500 Josh Poimboeuf ha dit:

> On Mon, Mar 19, 2018 at 04:22:55PM -0700, Matthias Kaehlcke wrote:
> > > Here's a (surprisingly easy) fix for this particular issue, though I'd
> > > be shocked if there weren't a bunch more issues lurking elsewhere.  Let
> > > me know how it goes.
> > 
> > Thanks for having a look, this fixes the vast majority of warnings in
> > a defconfig build!
> 
> Wow.  Consider me shocked :-)
> 
> > The remaining warnings are:
> > 
> > arch/x86/mm/pti.o: warning: objtool: pti_init() falls through to next
> > function pti_user_pagetable_walk_pmd()
> > s/debugfs/file.o: warning: objtool: full_proxy_llseek() falls through to next function full_proxy_read()
> > fs/debugfs/file.o: warning: objtool: full_proxy_read() falls through to next function full_proxy_write()
> > fs/debugfs/file.o: warning: objtool: full_proxy_write() falls through to next function full_proxy_poll()
> > fs/debugfs/file.o: warning: objtool: full_proxy_poll() falls through to next function full_proxy_unlocked_ioctl()
> > fs/debugfs/file.o: warning: objtool: full_proxy_unlocked_ioctl() falls through to next function fops_u8_open()
> 
> These all seem to be related to some weirdness with the UD2 instruction,
> not necessarily an objtool issue per se.
> 
> Any chance this fixes some of the warnings?  If not, I can try to build
> with clang and look a little deeper.
> 
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index ab4711c63601..315a8757b565 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -124,7 +124,12 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
>  # define ASM_UNREACHABLE
>  #endif
>  #ifndef unreachable
> -# define unreachable() do { annotate_reachable(); do { } while (1); } while (0)
> +#define unreachable() \
> +	do {					\
> +		annotate_unreachable();		\
> +		barrier_before_unreachable();	\
> +		__builtin_unreachable();	\
> +	} while (0)
>  #endif

Thanks, unfortunately negative on this one, all the warnings are still
generated.