Messages in this thread | | | Date | Sat, 12 Sep 2020 17:40:41 +0900 | From | Stafford Horne <> | Subject | Re: [PATCH v3 3/3] openrisc: Fix issue with get_user for 64-bit values |
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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
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