linux-kernel - Re: [PATCH] x86/kconfig: hide unwinder menu for KMEMCHECK

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Date:   Mon, 11 Sep 2017 18:42:30 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/kconfig: hide unwinder menu for KMEMCHECK

On Mon, Sep 11, 2017 at 09:59:36PM +0200, Arnd Bergmann wrote:
> When KMEMCHECK is enabled, we always build with frame pointers,
> which is incompatible with ORC_UNWINDER and GUESS_UNWINDER, as
> Kconfig points out:
> 
> warning: (FAULT_INJECTION_STACKTRACE_FILTER && LATENCYTOP && KMEMCHECK && LOCKDEP && FRAME_POINTER_UNWINDER) selects FRAME_POINTER which has unmet direct dependencies (DEBUG_KERNEL && (CRIS || M68K || FRV || UML || SUPERH || BLACKFIN || MN10300 || METAG) || ARCH_WANT_FRAME_POINTERS || !ORC_UNWINDER && !GUESS_UNWINDER)
> 
> This works around it by making those two unwinders depend on
> !KMEMCHECK. The other three options that enable frame pointers
> (FAULT_INJECTION_STACKTRACE_FILTER, LATENCYTOP and LOCKDEP) only
> do that on some architectures but not on x86.
> 
> It's possible that KMEMCHECK doesn't actually require frame pointers
> but only requires some unwinder. If that is the case, we should drop
> the 'select FRAME_POINTER' there. KMEMCHECK is currenly used only
> on x86.

KMEMCHECK should work with *any* of the unwinders because it uses the
unwinder-agnostic save_stack_trace() interface.  So removing the 'select
FRAME_POINTER' sounds like the right fix.

-- 
Josh