Re: [PATCH v2] kbuild: Enable -Wtautological-compare

[Nathan Chancellor <natechancellor@gmail.com>]

On Sun, Mar 29, 2020 at 08:31:26PM +0900, Masahiro Yamada wrote:
> On Fri, Mar 27, 2020 at 4:42 AM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > Currently, we disable -Wtautological-compare, which in turn disables a
> > bunch of more specific tautological comparison warnings that are useful
> > for the kernel such as -Wtautological-bitwise-compare. See clang's
> > documentation below for the other warnings that are suppressed by
> > -Wtautological-compare. Now that all of the major/noisy warnings have
> > been fixed, enable -Wtautological-compare so that more issues can be
> > caught at build time by various continuous integration setups.
> >
> > -Wtautological-constant-out-of-range-compare is kept disabled under a
> > normal build but visible at W=1 because there are places in the kernel
> > where a constant or variable size can change based on the kernel
> > configuration. These are not fixed in a clean/concise way and the ones
> > I have audited so far appear to be harmless. It is not a subgroup but
> > rather just one warning so we do not lose out on much coverage by
> > default.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/488
> > Link: http://releases.llvm.org/10.0.0/tools/clang/docs/DiagnosticsReference.html#wtautological-compare
> > Link: https://bugs.llvm.org/show_bug.cgi?id=42666
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > ---
> >
> > v1 -> v2: https://lore.kernel.org/lkml/20200219045423.54190-7-natechancellor@gmail.com/
> >
> > * Expand commit message a bit by adding more reasoning behind change.
> > * Disable -Wtautological-constant-out-of-range-compare under a normal
> >   build but allow it to show up at W=1 for easy auditing.
> >
> > I hope this can be accepted for 5.7. There are two warnings that I see
> > still across a bunch of allyesconfig/allmodconfig builds that have
> > patches sent but not accepted. I will ping them today.
> >
> > * https://lore.kernel.org/lkml/20191023002014.22571-1-natechancellor@gmail.com/
> > * https://lore.kernel.org/lkml/20200220051011.26113-1-natechancellor@gmail.com/
> 
> 
> OK, I will queue this up and send it to Linus
> in the second week of MW.
> 
> I hope all warnings will be fixed by that time.

Just a follow up, those two patches have been picked up and should be in
this coming release:

https://git.kernel.org/balbi/usb/c/58582220d2d34228e5a1e1585e41b735713988bb
https://git.kernel.org/rostedt/linux-trace/c/bf2cbe044da275021b2de5917240411a19e5c50d

As of next-20200331, with the former applied (because it is not there
yet) along with this patch, I see no warnings on arm, arm64, x86_64
all{mod,yes}config.

Cheers,
Nathan