[OS-BUILD PATCHv4] makefile: Add -Werror support for RHEL

[Prarit Bhargava (via Email Bridge)]

From: Prarit Bhargava <prarit(a)redhat.com&gt;

makefile: Add -Werror support for RHEL

The -Werror flag should be enabled for RHEL.  In ARK, however, it is a bit
tricky to enable -Werror as a build bug occasionally leaks through
upstream review and into Linus' tree.  As a consequence, CONFIG_WERROR
cannot be enabled in ARK but the code to add the flag for RHEL commpiles
can be added to the top-level makefile.

This code could be placed in the top-level Makefile, around the -Werror
line added by Linus in 3fe617ccafd6 ("Enable '-Werror' by default for all
kernel builds"), but given the amount of RHEL Only code here it is best to
keep it separated in our top-level makefile.  Reviewers should note that
there is no harm in calling 'KBUILD_CFLAGS += -Werror' twice and that
-Werror only appears once in gcc calls when compiling kernel files.

Signed-off-by: Prarit Bhargava <prarit(a)redhat.com&gt;

diff --git a/makefile b/makefile
index blahblah..blahblah 100644
--- a/makefile
+++ b/makefile
@@ -14,3 +14,14 @@ dist-%::
 distg-%::
 	$(MAKE) -C redhat $(@) $(_EXTRA_ARGS)
 
+# Enable -Werror for RHEL
+ifneq ($(DISABLE_WERROR),1)
+ifneq ($(WITH_GCOV),1)
+ifeq ($(KBUILD_EXTMOD),)
+ifneq (,$(filter $(ARCH), x86 x86_64 powerpc s390 aarch64))
+KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror
+KBUILD_CPPFLAGS += $(KBUILD_CPPFLAGS-y)
+endif
+endif
+endif
+endif

--
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/2240

[Prarit Bhargava (via Email Bridge)]

From: Prarit Bhargava on gitlab.com
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/2240#note_1230...

Yeah, I was a bit torn on this too for the same reasons; even with this change
we have to 'remember' to set CONFIG_WERROR which is lame.  One thing to keep
in mind is that it does seem like Linus *wants* CONFIG_WERROR on at some point
upstream.  He just hit too much push back so he backed off on it.  By the time
we need to think about turning on CONFIG_WERROR in RHEL it may have already
been done so by Linus so that we don't have to worry about it.

I'd like to hear from @jmflinuxtx and @ptalbert about how they feel about your
proposal.  They're the ones who have to deal with the fallout from
CONFIG_WERROR.  I'm okay with any choice made here, but I just want to make
sure I don't break ARK/Fedora.

[Justin M. Forbes (via Email Bridge)]

From: Justin M. Forbes on gitlab.com
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/2240#note_1230...

We are already building with `-Werror=format-security` Though we typically do
not run across many errors until a new toolchain is introduced. That is where
this gets problematic to turn on for ark, and where it is much less of a
problem for RHEL. Once a year, we get a new toolchain in Fedora. It is typical
that we get a massive number of kernel warnings when a new toolchain is
introduced.  Over time (usually a couple of release cycles, so months) those
warnings are fixed.  RHEL never has this problem.   Turning on full Werror in
ark will result in my having to chase down a whole bunch of fixes to keep the
tree building which would just land naturally long before RHEL needs them.