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    SubjectRe: [PATCH v3 3/3] openrisc: Fix issue with get_user for 64-bit values
    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>

    -- Luc

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