[PATCH] ARM: asm: Rewrite get_thread_info using BIC

[Dmitry Osipenko]

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 at armlinux.org.uk>
> Suggested-by: Ard Biesheuvel <ardb at kernel.org>
> Signed-off-by: Linus Walleij <linus.walleij at 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