Bug#954294: linux: __X32_SYSCALL_BIT being defined as UL constant breaks userspace (was Re: libseccomp-dev: API break: SCMP_SYS() is unsigned long (was Re: Bug#954294: systemd: FTBFS on x32 due to format string errors, need explicit casts))

[Thorsten Glaser <t.glaser@tarent.de>]

Dear kernel team,

libseccomp uses the __NR_* constants from <asm/unistd.h> in its
macro SCMP_SYS() which is designed to return int.

However, on x32 some codes return unsigned long instead, breaking this.
The cause is that this…

> /usr/include/x86_64-linux-gnux32/asm/unistd.h:#define __X32_SYSCALL_BIT 0x40000000UL

… is OR’d into the numbers.

I’d like to propose the change…
-#define __X32_SYSCALL_BIT 0x40000000UL
+#define __X32_SYSCALL_BIT 0x40000000
… which should be safe to do as the number fits into signed int,
but must be checked against other users (especially in the kernel
itself I’d guess).

This should also technically be correct, since on all(?) other
architectures syscall numbers are int constants.

Please forward this to upstream.

Thanks,
//mirabilos
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