linux-kernel - Re: [RFC v4 13/18] arm64: sleep: Prevent stack frame warnings from objtool

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Message-ID: <20190822201620.z7eto2cfjo4uaozb@treble>
Date:   Thu, 22 Aug 2019 15:16:20 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Raphael Gault <raphael.gault@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        peterz@...radead.org, catalin.marinas@....com, will.deacon@....com,
        julien.thierry.kdev@...il.com, raph.gault+kdev@...il.com
Subject: Re: [RFC v4 13/18] arm64: sleep: Prevent stack frame warnings from
 objtool

On Fri, Aug 16, 2019 at 01:23:58PM +0100, Raphael Gault wrote:
> This code doesn't respect the Arm PCS but it is intended this
> way. Adapting it to respect the PCS would result in altering the
> behaviour.
> 
> In order to suppress objtool's warnings, we setup a stack frame
> for __cpu_suspend_enter and annotate cpu_resume and _cpu_resume
> as having non-standard stack frames.
> 
> Signed-off-by: Raphael Gault <raphael.gault@....com>
> ---
>  arch/arm64/kernel/sleep.S | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S
> index f5b04dd8a710..55c7c099d32c 100644
> --- a/arch/arm64/kernel/sleep.S
> +++ b/arch/arm64/kernel/sleep.S
> @@ -1,5 +1,6 @@
>  /* SPDX-License-Identifier: GPL-2.0 */
>  #include <linux/errno.h>
> +#include <linux/frame.h>
>  #include <linux/linkage.h>
>  #include <asm/asm-offsets.h>
>  #include <asm/assembler.h>
> @@ -90,6 +91,7 @@ ENTRY(__cpu_suspend_enter)
>  	str	x0, [x1]
>  	add	x0, x0, #SLEEP_STACK_DATA_SYSTEM_REGS
>  	stp	x29, lr, [sp, #-16]!
> +	mov	x29, sp
>  	bl	cpu_do_suspend
>  	ldp	x29, lr, [sp], #16
>  	mov	x0, #1
> @@ -146,3 +148,6 @@ ENTRY(_cpu_resume)
>  	mov	x0, #0
>  	ret
>  ENDPROC(_cpu_resume)
> +
> +	asm_stack_frame_non_standard cpu_resume
> +	asm_stack_frame_non_standard _cpu_resume

We usually put these annotations immediately after the functions they're
annotating.  And they should resemble the C macros like

  STACK_FRAME_NON_STANDARD(cpu_resume)

-- 
Josh