Re: [PATCH 04/11] Define the virtual space of KASan's shadow region

From: Russell King - ARM Linux
Date: Thu Oct 19 2017 - 08:42:50 EST


On Mon, Oct 16, 2017 at 01:14:54PM +0100, Ard Biesheuvel wrote:
> On 16 October 2017 at 12:42, Liuwenliang (Lamb) <liuwenliang@xxxxxxxxxx> wrote:
> > On 10/16/2017 07:03 PM, Abbott Liu wrote:
> >>arch/arm/kernel/entry-armv.S:348: Error: selected processor does not support `movw r1,
> > #:lower16:((((0xC0000000-0x01000000)>>3)+((0xC0000000-0x01000000)-(1<<29))))' in ARM mode
> >>arch/arm/kernel/entry-armv.S:348: Error: selected processor does not support `movt r1,
> > #:upper16:((((0xC0000000-0x01000000)>>3)+((0xC0000000-0x01000000)-(1<<29))))' in ARM mode
> >
> > Thanks for building test. This error can be solved by following code:
> > --- a/arch/arm/kernel/entry-armv.S
> > +++ b/arch/arm/kernel/entry-armv.S
> > @@ -188,8 +188,7 @@ ENDPROC(__und_invalid)
> > get_thread_info tsk
> > ldr r0, [tsk, #TI_ADDR_LIMIT]
> > #ifdef CONFIG_KASAN
> > - movw r1, #:lower16:TASK_SIZE
> > - movt r1, #:upper16:TASK_SIZE
> > + ldr r1, =TASK_SIZE
> > #else
> > mov r1, #TASK_SIZE
> > #endif
>
> This is unnecessary:
>
> ldr r1, =TASK_SIZE
>
> will be converted to a mov instruction by the assembler if the value
> of TASK_SIZE fits its 12-bit immediate field.

It's an 8-bit immediate field for ARM.

What it won't do is expand it to a pair of movw/movt instructions if it
doesn't fit.

--
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