• Stafford Horne's avatar
    openrisc: Fix issue with get_user for 64-bit values · ad9ee9ce
    Stafford Horne authored
    commit d877322bc1adcab9850732275670409e8bcca4c4 upstream.
    
    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 in 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.
    
    Link: https://lore.kernel.org/lkml/202008200453.ohnhqkjQ%25lkp@intel.com/
    
    Signed-off-by: default avatarStafford Horne <shorne@gmail.com>
    Reviewed-by: default avatarLuc Van Oostenryck <luc.vanoostenryck@gmail.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    
    ad9ee9ce
uaccess.h 7.86 KB