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

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Date:   Thu, 19 Oct 2017 13:41:49 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     "Liuwenliang (Lamb)" <liuwenliang@...wei.com>,
        "tixy@...aro.org" <tixy@...aro.org>,
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Subject: Re: [PATCH 04/11] Define the virtual space of KASan's shadow region

On Mon, Oct 16, 2017 at 01:14:54PM +0100, Ard Biesheuvel wrote:
> On 16 October 2017 at 12:42, Liuwenliang (Lamb) <liuwenliang@...wei.com> 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.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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