-Wformat-trunctation with `make W=1`

-Wformat-trunctation with `make W=1`

[Andy Shevchenko]

Recently I'm trying to compile my (almost) x86_64_defconfig based kernel with
`make W=1` while having CONFIG_WERROR=y. With a handful of patches I was able
to achieve that with clang-18, however GCC 14.2.0 issues a lot of additional
warnings that are mostly related to -Wformat-truncation [1]. Any suggestions,
plans, comments on how to address them?

[1]: https://paste.debian.net/hidden/46106f2a/

-- 
With Best Regards,
Andy Shevchenko

Re: -Wformat-trunctation with `make W=1`

[Kees Cook]

On Mon, Sep 09, 2024 at 04:26:03PM +0300, Andy Shevchenko wrote:
> Recently I'm trying to compile my (almost) x86_64_defconfig based kernel with
> `make W=1` while having CONFIG_WERROR=y. With a handful of patches I was able
> to achieve that with clang-18, however GCC 14.2.0 issues a lot of additional
> warnings that are mostly related to -Wformat-truncation [1]. Any suggestions,
> plans, comments on how to address them?
> 
> [1]: https://paste.debian.net/hidden/46106f2a/

Since it's behind W=1, fixing those issues hasn't been a very high
priority. That said, I would love to see it done. Patches have slowly
been landing for various W=1 things related to the -Wstringop-... and
-Wformat... options, though. But I don't think there has been a
concerted effort to wipe them out completely. And at least sometimes
these warnings are effectively false positives, related to unexpected
behaviors in GCC's value range tracking, though that has mostly been an
issue for getting -Warray-bounds to build cleanly.

As for fixing them, I think one will need to just look at each instance
one at a time to figure out the best solution.

-Kees

-- 
Kees Cook

Re: -Wformat-trunctation with `make W=1`

[Arnd Bergmann]

On Wed, Sep 11, 2024, at 00:26, Kees Cook wrote:
> On Mon, Sep 09, 2024 at 04:26:03PM +0300, Andy Shevchenko wrote:
>> Recently I'm trying to compile my (almost) x86_64_defconfig based kernel with
>> `make W=1` while having CONFIG_WERROR=y. With a handful of patches I was able
>> to achieve that with clang-18, however GCC 14.2.0 issues a lot of additional
>> warnings that are mostly related to -Wformat-truncation [1]. Any suggestions,
>> plans, comments on how to address them?
>> 
>> [1]: https://paste.debian.net/hidden/46106f2a/
>
> Since it's behind W=1, fixing those issues hasn't been a very high
> priority. That said, I would love to see it done. Patches have slowly
> been landing for various W=1 things related to the -Wstringop-... and
> -Wformat... options, though. But I don't think there has been a
> concerted effort to wipe them out completely. And at least sometimes
> these warnings are effectively false positives, related to unexpected
> behaviors in GCC's value range tracking, though that has mostly been an
> issue for getting -Warray-bounds to build cleanly.
>
> As for fixing them, I think one will need to just look at each instance
> one at a time to figure out the best solution.

I have a series from earlier this year, let me see what I had
in there:

 -Wformat-truncation triggers in 133 files with arm64 allmodconfig,
  which is more than any other W=1 warnings. Addressing them
  individually is probably a good idea, but most of the other
  W=1 warnings seem more helpful if we can just enable them
  after a few patches.
 -Wformat-truncation-non-kprintf only happens in a single file
  and we should fix that. We can probably just enable the
  default -Wformat warnings on clang at last..
 -Wunused-const-variable=2 needs a lot of patches but they are
  all trivial (mostly extraneous of_match_ptr()), just need to
  be split up better. My tree builds  randconfig cleanly with
  this enabled.
 -Wtautological-constant-out-of-range-compare needs four
  more patches that I have sent previously
 -Wstringop-truncation can be enabled globally
 -Woverride-init just needs to be disabled in a couple of
  key places that intentionally use defaults
 -Wmissing-format-attribute triggers in only 9 files, but
  I don't think I have patches for those.
 -Wformat-overflow= triggers in 15 files with gcc but 35 with
  clang, I don't have patches for these.
 -Wunused-but-set-variable triggers in 8 files, I sent some
  patches for these in the past.
 -Wenum-enum-conversion has 93 files with warnings in clang-20
 -Wvoid-pointer-to-enum-cast shows up in 19 files with clang-20

       Arnd