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

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Message-ID: <2023052247-bobtail-factsheet-d104@gregkh>
Date:   Mon, 22 May 2023 17:52:32 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ricardo Cañuelo <ricardo.canuelo@...labora.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Shreeya Patel <shreeya.patel@...labora.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        Bill Wendling <morbo@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        regressions@...ts.linux.dev,
        "gustavo.padovan@...labora.com" <gustavo.padovan@...labora.com>,
        Guillaume Charles Tucker <guillaume.tucker@...labora.com>,
        denys.f@...labora.com, kernelci@...ts.linux.dev
Subject: Re: [PATCH v4] Makefile.compiler: replace cc-ifversion with
 compiler-specific macros

On Mon, May 22, 2023 at 12:09:34PM +0200, Ricardo Cañuelo wrote:
> On vie, may 19 2023 at 08:57:24, Nick Desaulniers <ndesaulniers@...gle.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]:

Yes, it matters, you can not change it.  If you do, systems will break.
It is the only way we have of properly ordering our init calls within
the same "level".

thanks,

greg k-h