linux-kernel - Re: [PATCH] powerpc/vdso32: Add missing _restgpr_31

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Date:   Fri, 12 Mar 2021 14:09:04 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/vdso32: Add missing _restgpr_31_x to fix build
 failure



Le 09/03/2021 à 07:19, Christophe Leroy a écrit :
> With some defconfig including CONFIG_CC_OPTIMIZE_FOR_SIZE,
> (for instance mvme5100_defconfig and ps3_defconfig), gcc 5
> generates a call to _restgpr_31_x.
> 
> Until recently it went unnoticed, but
> commit 42ed6d56ade2 ("powerpc/vdso: Block R_PPC_REL24 relocations")
> made it rise to the surface.
> 
> Provide that function (copied from lib/crtsavres.S) in
> gettimeofday.S
> 
> Fixes: ab037dd87a2f ("powerpc/vdso: Switch VDSO to generic C implementation.")
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>

Fixes the following builds:

http://kisskb.ellerman.id.au/kisskb/buildresult/14492138/
http://kisskb.ellerman.id.au/kisskb/buildresult/14492041/

Christophe


> ---
> I don't know if there is a way to tell GCC not to emit that call, because at the end we get more instructions than needed.
> ---
>   arch/powerpc/kernel/vdso32/gettimeofday.S | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/vdso32/gettimeofday.S b/arch/powerpc/kernel/vdso32/gettimeofday.S
> index a6e29f880e0e..d21d08140a5e 100644
> --- a/arch/powerpc/kernel/vdso32/gettimeofday.S
> +++ b/arch/powerpc/kernel/vdso32/gettimeofday.S
> @@ -65,3 +65,14 @@ V_FUNCTION_END(__kernel_clock_getres)
>   V_FUNCTION_BEGIN(__kernel_time)
>   	cvdso_call_time __c_kernel_time
>   V_FUNCTION_END(__kernel_time)
> +
> +/* Routines for restoring integer registers, called by the compiler.  */
> +/* Called with r11 pointing to the stack header word of the caller of the */
> +/* function, just beyond the end of the integer restore area.  */
> +_GLOBAL(_restgpr_31_x)
> +_GLOBAL(_rest32gpr_31_x)
> +	lwz	r0,4(r11)
> +	lwz	r31,-4(r11)
> +	mtlr	r0
> +	mr	r1,r11
> +	blr
>