From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-xfs <linux-xfs@vger.kernel.org>
Subject: Re: Build regressions/improvements in v5.18-rc1
Date: Tue, 5 Apr 2022 08:47:40 +0200 [thread overview]
Message-ID: <CAMuHMdWak-zarKA_eCxWm5uhejWAXi0XkAuekfpAKRczLfhq3g@mail.gmail.com> (raw)
In-Reply-To: <20220404221605.GS1544202@dread.disaster.area>
Hi Dave,
On Tue, Apr 5, 2022 at 12:16 AM Dave Chinner <david@fromorbit.com> wrote:
> On Mon, Apr 04, 2022 at 01:45:05PM +0200, Arnd Bergmann wrote:
> > On Mon, Apr 4, 2022 at 12:19 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > > /kisskb/src/fs/xfs/./xfs_trace.h:432:2: note: in expansion of macro 'TP_printk'
> > > > TP_printk("dev %d:%d daddr 0x%llx bbcount 0x%x hold %d pincount %d "
> > > > ^
> > > > /kisskb/src/fs/xfs/./xfs_trace.h:440:5: note: in expansion of macro '__print_flags'
> > > > __print_flags(__entry->flags, "|", XFS_BUF_FLAGS),
> > > > ^
> > > > /kisskb/src/fs/xfs/xfs_buf.h:67:4: note: in expansion of macro 'XBF_UNMAPPED'
> > > > { XBF_UNMAPPED, "UNMAPPED" }
> > > > ^
> > > > /kisskb/src/fs/xfs/./xfs_trace.h:440:40: note: in expansion of macro 'XFS_BUF_FLAGS'
> > > > __print_flags(__entry->flags, "|", XFS_BUF_FLAGS),
> > > > ^
> > > > /kisskb/src/fs/xfs/./xfs_trace.h: In function 'trace_raw_output_xfs_buf_flags_class':
> > > > /kisskb/src/fs/xfs/xfs_buf.h:46:23: error: initializer element is not constant
> > > > #define XBF_UNMAPPED (1 << 31)/* do not map the buffer */
> > > >
> > > > This doesn't make a whole lotta sense to me. It's blown up in a
> > > > tracepoint macro in XFS that was not changed at all in 5.18-rc1, nor
> > > > was any of the surrounding XFS code or contexts. Perhaps something
> > > > outside XFS changed to cause this on these platforms?
> > >
> > > Upon closer look, all builds showing this issue are using gcc-5...
> > >
> > > > Can you bisect this, please?
> > >
> > > Fortunately I still have gcc-5 installed on an older machine,
> > > and I could reproduce the issue on amd64 with
> > > "make allmodconfig fs/xfs/xfs_trace.o".
> > >
> > > Bisection points to commit e8c07082a810fbb9 ("Kbuild: move to
> > > -std=gnu11").
> > >
> > > [1] gcc version 5.5.0 20171010 (Ubuntu 5.5.0-12ubuntu1
> >
> > Thanks for the report. I've produced it and can see that the problem
> > is assigning
> > the value of "(1 << 31)" to an 'unsigned long' struct member. Since this is
> > a signed integer overflow, the result is technically undefined behavior,
> > which gcc-5 does not accept as an integer constant.
> >
> > The patch below fixes it for me, but I have not checked if there are any
> > other instances. This could also be done using the 'BIT()' macro if the
> > XFS maintainers prefer:
>
> So XFS only uses these flags in unsigned int fields that are
> typed via:
>
> typedef unsigned int xfs_buf_flags_t;
>
> So on the surface, declaring the flag values as ULONG and then writing
> them into a UINT field is not a nice thing to be doing.
>
> I really don't want to change the xfs_buf_flags_t type to an
> unsigned long, because that changes the packing of the first
> cacheline of the struct xfs_buf and the contents of that cacheline
> are performance critical for the lookup fastpath....
Hence just use "1u << n" instead of "1ul << n"?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2022-04-05 6:48 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-03 22:14 Linux 5.18-rc1 Linus Torvalds
2022-04-04 2:22 ` Guenter Roeck
2022-04-04 3:29 ` Linus Torvalds
2022-04-04 4:23 ` Guenter Roeck
2022-04-04 7:30 ` Ron Economos
2022-04-04 15:32 ` Linus Torvalds
2022-04-04 16:21 ` Greg Kroah-Hartman
2022-04-04 16:45 ` Guenter Roeck
2022-04-04 17:09 ` Linus Torvalds
2022-04-05 21:14 ` Konstantin Ryabitsev
2022-04-04 6:01 ` Jiri Slaby
2022-04-05 12:19 ` Sudip Mukherjee
2022-04-05 13:18 ` Guenter Roeck
2022-04-04 7:47 ` Build regressions/improvements in v5.18-rc1 Geert Uytterhoeven
2022-04-04 8:16 ` Geert Uytterhoeven
2022-04-04 9:26 ` Dave Chinner
2022-04-04 10:19 ` Geert Uytterhoeven
2022-04-04 11:45 ` Arnd Bergmann
2022-04-04 12:31 ` Arnd Bergmann
2022-04-04 22:16 ` Dave Chinner
2022-04-05 6:47 ` Geert Uytterhoeven [this message]
2022-04-05 7:08 ` Arnd Bergmann
2022-04-05 21:05 ` Dave Chinner
2022-04-04 18:39 ` Kalle Valo
2022-04-05 6:46 ` Geert Uytterhoeven
2022-04-05 6:52 ` Kalle Valo
2022-04-05 6:45 ` Helge Deller
2022-04-05 6:49 ` Geert Uytterhoeven
2022-04-28 7:25 ` Michael Ellerman
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