On Wed, May 10, 2017 at 3:40 PM, Segher Boessenkool
[off-list ref] wrote:

Hi Arnd, long time no see,

On Wed, May 10, 2017 at 09:58:13AM +0200, Arnd Bergmann wrote:

quoted

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So in addition to GCC 7.1 I'd like to have at least GCC 6.3 around,
which builds kernels without warnings today.

If you don't want warnings, turn off the warnings or just don't look at
them...  or fix the problems?  Many of the new warnings point out actual
problems.

Many of those sprintf problems in the kernel have already been fixed.

I've been using gcc-7.0 for a long time and fixed a lot of bugs it found,
along with more harmless warnings, but I had disabled a couple of
warning options when I first installed gcc-7 and ended up ignoring
those.

The exact set of additional options I used is:

-Wimplicit-fallthrough=0 -Wno-duplicate-decl-specifier
-Wno-int-in-bool-context -Wno-bool-operation -Wno-format-truncation
-Wno-format-overflow

there were a couple of others that I sent kernel fixes for instead.
I should probably revisit that list and for each of them either
only enable it with "make W=1" or fix all known warnings.
In the long run, I'd actually hope to fix all W=1 warnings too
and enable them by default.

Most of those usually point out actual problems (at least code that
isn't as clear as it should be).  I do hate that first one though.

My point is that we have others in W=1 some of which are equally useful:
warning-1 := -Wextra -Wunused -Wno-unused-parameter
warning-1 += -Wmissing-declarations
warning-1 += -Wmissing-format-attribute
warning-1 += $(call cc-option, -Wmissing-prototypes)
warning-1 += -Wold-style-definition
warning-1 += $(call cc-option, -Wmissing-include-dirs)
warning-1 += $(call cc-option, -Wunused-but-set-variable)
warning-1 += $(call cc-option, -Wunused-const-variable)
warning-1 += $(call cc-disable-warning, missing-field-initializers)
warning-1 += $(call cc-disable-warning, sign-compare)

I've looked through arm and x86  gcc-7 allmodconfig builds (without
my longish fixup series) again and found these added warnings
compared to gcc-6.3.1 overall:

      2 -Werror=bool-operation
      4 -Werror=maybe-uninitialized
      1 -Werror=parentheses
      2 -Werror=stringop-overflow=
      2 -Werror=tautological-compare

I probably submitted patches for those in the past, will have
another look to see if I need to resubmit them, or if some
of them might be regressions.

   148 -Werror=duplicate-decl-specifier

Only a few files are affected, I can take care of fixing them all:

  |      1 arch/arm/mach-at91/pm.c
  |      1 arch/arm/mach-bcm/bcm_kona_smc.c
  |      1 arch/arm/mach-cns3xxx/core.c
  |      1 arch/arm/mach-omap2/prm_common.c
  |      1 arch/arm/mach-omap2/vc.c
  |      1 arch/arm/mach-spear/time.c
  |      2 drivers/input/keyboard/cros_ec_keyb.c
  |      4 sound/soc/codecs/rt5514.c
  |    136 sound/soc/codecs/rt5665.c

     89 -Werror=int-in-bool-context

This showed up in 26 files in allmodconfig alone. I had started on some
of them but given up at some point. I can certainly submit the ones
I did already, but probably won't have the patience to address all of them
myself.

     54 -Werror=format-overflow=

Same here.

    494 -Werror=format-truncation=

These are all over the place, in 187 files.

The last one in particular seems less useful than -Wformat-security
which we already disable (for all levels), and I'd rather have them both in
"make W=1". For -Wint-in-bool-context and -Wformat-overflow=
it's less obvious whether we should try to get them all fixed
quickly, using >100 patches or put them into W=1 along with
-Wformat-truncation.

      Arnd