* Segher Boessenkool:
> On Wed, Jan 29, 2020 at 05:19:19PM +0100, Florian Weimer wrote:
>> * Segher Boessenkool:
>> >> But GCC doesn't expose them as integers to C code, so you can't do much
>> >> without them.
>> >
>> > Sure, it doesn't expose any other registers directly, either.
>>
>> I can use r0 & 1 with a register variable r0 to check a bit.
>
> That is not reliable, or supported, and it *will* break. This is
> explicit for local register asm, and global register asm is
> underdefined.
Ugh. I did not know that. And neither did the person who wrote
powerpc64/sysdep.h because it uses register variables in regular C
expressions. 8-( Other architectures are affected as well.
One set of issues is less of a problem if system call arguments are
variables and not complex expressions, so that side effects do not
clobber registers in the initialization:
register long __a0 asm ("$4") = (long) (arg1);
But I wasn't aware of that constraint on the macro users at all.
Thanks,
Florian
