linux-kernel - Re: older gccs and case labels producing integer constants

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Message-ID: <YkwdtxNCpiERLFGW@zn.tnic>
Date:   Tue, 5 Apr 2022 12:45:11 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Richard Biener <rguenther@...e.de>
Cc:     linux-toolchains@...r.kernel.org, Michael Matz <matz@...e.de>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: older gccs and case labels producing integer constants

On Tue, Apr 05, 2022 at 12:36:58PM +0200, Borislav Petkov wrote:
> On Tue, Apr 05, 2022 at 12:06:45PM +0200, Richard Biener wrote:
> > Wird auch mit gcc 11 rejected.  Kanns sein dass mit gcc 7 andere
> > compiler flags genommen werden?
> 
> Found it:
> 
> $ gcc -fsanitize=shift -c switch.c
> switch.c: In function ‘foo’:
> switch.c:10:7: error: case label does not reduce to an integer constant
>        case (((0xfc08) << 16) | (0x0101)):;
> 
> $ gcc --version
> gcc (SUSE Linux) 7.4.1 20190905 [gcc-7-branch revision 275407]
> Copyright (C) 2017 Free Software Foundation, Inc.
> 
> Something not fully backported?

Ok, not really:

gcc-10 -fsanitize=shift -c switch.c
switch.c: In function ‘foo’:
switch.c:10:7: error: case label does not reduce to an integer constant
   10 |       case (((0xfc08) << 16) | (0x0101)):;
      |       ^~~~

BUT!

when more switches are set with gcc-10 (full gcc cmdline from a kernel
build), then that passes.

But it doesn't pass with gcc-7.

Weird...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette