linux-kernel - Re: [PATCH v6 10/10] x86/retpoline: Exclude objtool with retpoline

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Date:   Mon, 8 Jan 2018 11:25:04 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Woodhouse <dwmw@...zon.co.uk>
cc:     Andi Kleen <ak@...ux.intel.com>, Paul Turner <pjt@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk
Subject: Re: [PATCH v6 10/10] x86/retpoline: Exclude objtool with retpoline

On Sun, 7 Jan 2018, David Woodhouse wrote:

Cc+ Josh Poimboeuf <jpoimboe@...hat.com>

Sigh....

> From: Andi Kleen <ak@...ux.intel.com>
> 
> objtool's assembler nanny currently cannot deal with the code generated
> by the retpoline compiler and throws hundreds of warnings, mostly
> because it sees calls that don't have a symbolic target.
> 
> Exclude all the options that rely on objtool when RETPOLINE is active.
> 
> This mainly means that we use the frame pointer unwinder and livepatch
> is not supported.
> 
> Eventually objtool can be fixed to handle this.
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Acked-By: Arjan van de Ven <arjan@...ux.intel.com>
> ---
>  arch/x86/Kconfig       | 4 ++--
>  arch/x86/Kconfig.debug | 6 +++---
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 77c58ae..651d25f 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -171,8 +171,8 @@ config X86
>  	select HAVE_PERF_USER_STACK_DUMP
>  	select HAVE_RCU_TABLE_FREE
>  	select HAVE_REGS_AND_STACK_ACCESS_API
> -	select HAVE_RELIABLE_STACKTRACE		if X86_64 && UNWINDER_FRAME_POINTER && STACK_VALIDATION
> -	select HAVE_STACK_VALIDATION		if X86_64
> +	select HAVE_RELIABLE_STACKTRACE		if X86_64 && UNWINDER_FRAME_POINTER && STACK_VALIDATION && !RETPOLINE
> +	select HAVE_STACK_VALIDATION		if X86_64 && !RETPOLINE
>  	select HAVE_SYSCALL_TRACEPOINTS
>  	select HAVE_UNSTABLE_SCHED_CLOCK
>  	select HAVE_USER_RETURN_NOTIFIER
> diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
> index 6293a87..9f3928d 100644
> --- a/arch/x86/Kconfig.debug
> +++ b/arch/x86/Kconfig.debug
> @@ -359,8 +359,8 @@ config PUNIT_ATOM_DEBUG
>  
>  choice
>  	prompt "Choose kernel unwinder"
> -	default UNWINDER_ORC if X86_64
> -	default UNWINDER_FRAME_POINTER if X86_32
> +	default UNWINDER_ORC if X86_64 && !RETPOLINE
> +	default UNWINDER_FRAME_POINTER if X86_32 || RETPOLINE
>  	---help---
>  	  This determines which method will be used for unwinding kernel stack
>  	  traces for panics, oopses, bugs, warnings, perf, /proc/<pid>/stack,
> @@ -368,7 +368,7 @@ choice
>  
>  config UNWINDER_ORC
>  	bool "ORC unwinder"
> -	depends on X86_64
> +	depends on X86_64 && !RETPOLINE
>  	select STACK_VALIDATION
>  	---help---
>  	  This option enables the ORC (Oops Rewind Capability) unwinder for
> -- 
> 2.7.4
> 
>