lkml.org 
[lkml]   [2020]   [Sep]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 3/3] openrisc: Fix issue with get_user for 64-bit values
On Fri, Sep 11, 2020 at 10:55:26PM +0200, Luc Van Oostenryck wrote:
> On Fri, Sep 11, 2020 at 08:39:40AM +0900, Stafford Horne wrote:
> > A build failure was raised by kbuild with the following error.
> >
> > drivers/android/binder.c: Assembler messages:
> > drivers/android/binder.c:3861: Error: unrecognized keyword/register name `l.lwz ?ap,4(r24)'
> > drivers/android/binder.c:3866: Error: unrecognized keyword/register name `l.addi ?ap,r0,0'
> >
> > The issue is with 64-bit get_user() calls on openrisc. I traced this to
> > a problem where in the internally in the get_user macros there is a cast
> > to long __gu_val this causes GCC to think the get_user call is 32-bit.
> > This binder code is really long and GCC allocates register r30, which
> > triggers the issue. The 64-bit get_user asm tries to get the 64-bit pair
> > register, which for r30 overflows the general register names and returns
> > the dummy register ?ap.
> >
> > The fix here is to move the temporary variables into the asm macros. We
> > use a 32-bit __gu_tmp for 32-bit and smaller macro and a 64-bit tmp in
> > the 64-bit macro. The cast in the 64-bit macro has a trick of casting
> > through __typeof__((x)-(x)) which avoids the below warning. This was
> > barrowed from riscv.
> >
> > arch/openrisc/include/asm/uaccess.h:240:8: warning: cast to pointer from integer of different size
> >
> > I tested this is a small unit test to check reading between 64-bit and
> > 32-bit pointers to 64-bit and 32-bit values in all combinations. Also I
> > ran make C=1 to confirm no new sparse warnings came up. It all looks
> > clean to me.
>
> It looks correct to me too now at C & assembly level.
> Feel free to add my:
> Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>

Thanks a lot.

-Stafford

\
 
 \ /
  Last update: 2020-09-12 10:40    [W:0.200 / U:0.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site