Re: [PATCH] ARM: asm: Rewrite get_thread_info using BIC - Russell King

From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>,
	Ard Biesheuvel <ardb@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] ARM: asm: Rewrite get_thread_info using BIC
Date: Tue, 21 Jul 2020 14:38:38 +0100	[thread overview]
Message-ID: <20200721133838.GZ1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <b8a361f8-2b61-b8d1-9405-0830e2b0be89@gmail.com>

On Tue, Jul 21, 2020 at 04:37:09PM +0300, Dmitry Osipenko wrote:
> 27.05.2020 15:22, Linus Walleij пишет:
> > By using two BIC instructions we can replace the ARM/thumb
> > split instructions with something that works on either
> > and also save one instruction.
> > 
> > Based on code from proc-macros.S and an idea from Ard
> > Biesheuvel.
> > 
> > We need to include <linux/const.h> to expand the
> > THREAD_SIZE definition properly in the preprocessor.
> > 
> > Suggested-by: Russell King <linux@armlinux.org.uk>
> > Suggested-by: Ard Biesheuvel <ardb@kernel.org>
> > Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> > ---
> >  arch/arm/include/asm/assembler.h | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
> > index 99929122dad7..f218e8cf7f88 100644
> > --- a/arch/arm/include/asm/assembler.h
> > +++ b/arch/arm/include/asm/assembler.h
> > @@ -17,6 +17,7 @@
> >  #error "Only include this from assembly code"
> >  #endif
> >  
> > +#include <linux/const.h>
> >  #include <asm/ptrace.h>
> >  #include <asm/domain.h>
> >  #include <asm/opcodes-virt.h>
> > @@ -203,10 +204,8 @@
> >   * Get current thread_info.
> >   */
> >  	.macro	get_thread_info, rd
> > - ARM(	mov	\rd, sp, lsr #THREAD_SIZE_ORDER + PAGE_SHIFT	)
> > - THUMB(	mov	\rd, sp			)
> > - THUMB(	lsr	\rd, \rd, #THREAD_SIZE_ORDER + PAGE_SHIFT	)
> > -	mov	\rd, \rd, lsl #THREAD_SIZE_ORDER + PAGE_SHIFT
> > +	bic	\rd, sp, #(THREAD_SIZE - 1) & ~63
> > +	bic	\rd, \rd, #63
> >  	.endm
> >  
> >  /*
> > 
> 
> Hello, Linus!
> 
> This patch was merged into a recent linux-next, unfortunately it breaks
> CONFIG_THUMB2_KERNEL=y compilation:
> 
> arch/arm/kernel/entry-common.S: Assembler messages:
> arch/arm/kernel/entry-common.S:159: Error: r13 not allowed here -- `bic
> tsk,sp,#(((1<<12)<<1)-1)&~63'
> arch/arm/kernel/entry-common.S:246: Error: r13 not allowed here -- `bic
> tsk,sp,#(((1<<12)<<1)-1)&~63'
> make[2]: *** [scripts/Makefile.build:361:
> arch/arm/kernel/entry-common.o] Error 1

I've dropped it before you sent this email...

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel