Warning: unpredictable: identical transfer and status registers --`stxr w4,x5,[x4] using aarch64 poky gcc 8.3

[Michael Matz]

Hi,

On Wed, 13 Feb 2019, Peng Fan wrote:

>                 asm volatile (
>                         "ldxr   %3, %2\n\t"
>                         "ands   %1, %3, %4\n\t"
>                         "b.ne   1f\n\t"
>                         "orr    %3, %3, %4\n\t"
>                         "1:\n\t"
>                         "stxr   %w0, %3, %2\n\t"
>                         "dmb    ish\n\t"
>                         : "=r" (ret), "=&r" (test),
>                           "+Q" (*(volatile unsigned long *)addr),
>                           "=r" (tmp)
>                         : "r" (1ul << nr));

As Andreas says, you need to add an early-clobber for op3 for correctness 
(to force it into a different register from op4).  And you also need an 
early-clobber on op0 to force it into a different register from op2 (which 
for purposes of register assignment is an input operand holding an 
address).


Ciao,
Michael.