older gccs and case labels producing integer constants

From: Borislav Petkov
Date: Tue Apr 05 2022 - 20:22:10 EST

Hi folks,

I'm starting to see failures like this on allmodconfig builds:

sound/usb/midi.c: In function ‘snd_usbmidi_out_endpoint_create’:
sound/usb/midi.c:1389:2: error: case label does not reduce to an integer constant
case (((0xfc08) << 16) | (0x0101)):

(The case statement is a macro but it evaluates to what I have there)

and that thing fails with

$ gcc --version
gcc (SUSE Linux) 7.5.0

although it doesn't have any problems building with newer compilers.

I'm presuming older gccs consider those case statements signed ints and
the following fixes it:

case ((((unsigned int)0xfc08) << 16) | (0x0101)):

and I guess we can whack the couple of occurrences but what I'm
wondering is why does this work with newer gccs?