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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 13 Oct 2022 14:08:22 -0700
Message-ID: <CAKwvOd=_gfTD24zEh9YpoNuBr_D+xjsefeb8sNXnSaU_UgnVRw@mail.gmail.com>
Subject: Re: gcc 5 & 6 & others already out of date?
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     linux-toolchains@vger.kernel.org,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Oct 12, 2022 at 6:37 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> Hi,
>
> I've been working on a (still in development) patch that tries to
> apply a few compile-time constant folding tricks to a widely used
> library function, so I wanted to make sure my trickery worked across
> all supported gcc versions for as many call sites as possible.

I'd imagine the kernel's inconsistent use of -ffreestanding per
architecture would be a blocker, if by library function you're
referring to a symbol that would typically be provided by the libc?

Do you have more info about what the specific issue you've observed is?

> Naturally, this means allyesconfig builds on the monster box.
>
> So all went well with a recent gcc and with clang. Then I tried gcc 5
> and gcc 6, and it wasn't fine. But it wasn't not fine because of my
> new code -- that all compiled just fine. Rather, it wasn't fine
> because of a modicum of other odd errors and fatal warnings
> throughout. I tried this with gcc 5 and gcc 6 and then got bored. I
> could test more versions need be. And I guess I could submit bug
> reports or write patches or work on fixing all those, if I actually
> cared about it. But I don't really care about it, and apparently
> neither does anybody else, because this isn't brand new breakage. And
> this all got me thinking...

Are the defconfigs totally broken with gcc-5 and gcc-6 and no one has noticed?

I wonder what versions of GCC KernelCI and linux kernel robot are testing with?

We have to maintain CI for all supported clang versions. You can see a
2D slice of our 5D build matrix: https://clangbuiltlinux.github.io/.
"I've never seen so much red in the galaxy!" "Hey, get back to work!"

We'd like to have the large window of supported versions that GCC
currently has; Clang's release cycle is also different from GCC's
though.  I wouldn't point to clang's smaller version support window as
justification for GCC; we'd rather be more like GCC in that sense, not
the other way round!
-- 
Thanks,
~Nick Desaulniers