Bug#954294: __X32_SYSCALL_BIT being defined as UL constant breaks userspace

[Thomas Gleixner <tglx@linutronix.de>]

Andy Lutomirski <luto@kernel.org> writes:
> On Wed, Apr 8, 2020 at 7:34 AM Thorsten Glaser <t.glaser@tarent.de> wrote:
>> asm/unistd_x32.h:#define __NR_mmap (__X32_SYSCALL_BIT + 9)
>>
>> This construct is, thankfully, still usable in something like
>>         #if (__NR_mmap > __NR_somethingelse)
>> but as __X32_SYSCALL_BIT is no longer int its type also isn’t.
>>
>> Therefore I ask you to revert this change, bringing x32 closer
>> to all other architectures.
>>
>
> One might reasonably ask whether it makes sense for syscall nrs to be
> signed at all.
>
> But regardless, this breaks userspace and we should fix it.  I can
> whip up a patch to split it into X32_SYSCALL_BIT (unsigned long) and
> __X32_SYSCALL_BIT (uapi, int).  Thomas, etc, does this seem
> reasonable?  (For those not following all the machinations, this
> change caused some userspace build failures in libseccomp and/or
> systemd for reasons that are vaguely silly.)

Yes.