Re: [PATCH v4] Makefile.compiler: replace cc-ifversion with compiler-specific macros

From: "Ricardo Cañuelo" <ricardo.canuelo@collabora.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Shreeya Patel <shreeya.patel@collabora.com>,
	Michal Marek <michal.lkml@markovi.net>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <llvm@lists.linux.dev>,
	Bill Wendling <morbo@google.com>,
	Nathan Chancellor <nathan@kernel.org>,
	regressions@lists.linux.dev,
	"gustavo.padovan\@collabora.com" <gustavo.padovan@collabora.com>,
	Guillaume Charles Tucker <guillaume.tucker@collabora.com>,
	denys.f@collabora.com, kernelci@lists.linux.dev,
	Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v4] Makefile.compiler: replace cc-ifversion with compiler-specific macros
Date: Mon, 22 May 2023 12:09:34 +0200	[thread overview]
Message-ID: <87353ok78h.fsf@rcn-XPS-13-9305.i-did-not-set--mail-host-address--so-tickle-me> (raw)
In-Reply-To: <CAKwvOdmJJibt6sHSp91v2s7BxUWBC6xG7F7+3C6gUxNMzZ2xRA@mail.gmail.com>

On vie, may 19 2023 at 08:57:24, Nick Desaulniers <ndesaulniers@google.com> wrote:
> It could be; if the link order was changed, it's possible that this
> target may be hitting something along the lines of:
> https://isocpp.org/wiki/faq/ctors#static-init-order i.e. the "static
> initialization order fiasco"
>
> I'm struggling to think of how this appears in C codebases, but I
> swear years ago I had a discussion with GKH (maybe?) about this. I
> think I was playing with converting Kbuild to use Ninja rather than
> Make; the resulting kernel image wouldn't boot because I had modified
> the order the object files were linked in.  If you were to randomly
> shuffle the object files in the kernel, I recall some hazard that may
> prevent boot.

I thought that was specifically a C++ problem? But then again, the
kernel docs explicitly say that the ordering of obj-y goals in kbuild is
significant in some instances [1]:

    --- 3.2 Built-in object goals - obj-y

    [...]

    Link order is significant, because certain functions (module_init()
    / __initcall) will be called during boot in the order they
    appear. So keep in mind that changing the link order may e.g. change
    the order in which your SCSI controllers are detected, and thus your
    disks are renumbered.

We'll dig deeper into this. Thanks for your insight.

Cheers,
Ricardo

[1]: https://www.kernel.org/doc/Documentation/kbuild/makefiles.txt