Re: [PATCH] Enable '-Werror' by default for all kernel builds

On Thu, 9 Sept 2021 at 13:00, Arnd Bergmann [off-list ref] wrote:

On Thu, Sep 9, 2021 at 12:54 PM Marco Elver [off-list ref] wrote:

quoted

On Thu, 9 Sept 2021 at 07:59, Christoph Hellwig [off-list ref] wrote:

quoted

On Wed, Sep 08, 2021 at 11:58:56PM +0200, Marco Elver wrote:

quoted

It'd be good to avoid. It has helped uncover build issues with KASAN in
the past. Or at least make it dependent on the problematic architecture.
For example if arm is a problem, something like this:

I'm also seeing quite a few stack size warnings with KASAN on x86_64
without COMPILT_TEST using gcc 10.2.1 from Debian.  In fact there are a
few warnings without KASAN, but with KASAN there are a lot more.
I'll try to find some time to dig into them.

Right, this reminded me that we actually at least double the real
stack size for KASAN builds, because it inherently requires more stack
space. I think we need Wframe-larger-than to match that, otherwise
we'll just keep having this problem:

https://lkml.kernel.org/r/20210909104925.809674-1-elver@google.com

The problem with this is that it completely defeats the point of the
stack size warnings in allmodconfig kernels when they have KASAN
enabled and end up missing obvious code bugs in drivers that put
large structures on the stack. Let's not go there.

Sure, but the reality is that the real stack size is already doubled
for KASAN. And that should be reflected in Wframe-larger-than.

Either that, or we just have to live with the occasional warning (that
is likely benign). But with WERROR we're now forced to make the
defaults as sane as possible. If the worry is allmodconfig, maybe we
do have to make KASAN dependent on !COMPILE_TEST, even though that's
not great either because it has caught real issues in the past (it'll
also mean doing the same for all other instrumentation-based tools,
like KCSAN, UBSAN, etc.).