linux-kernel - Re: [PATCH v3 4/4] kernel hacking: new config CC_OPTIMIZE_FOR

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Message-ID: <CAK7LNAS8UPXBbOpG9Zy_aP7an2jbq5H7uQGymUAn+hv46WQ4Bw@mail.gmail.com>
Date:   Mon, 29 Oct 2018 22:16:02 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Steven Rostedt <rostedt@...dmis.org>, X86 ML <x86@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-sparse@...r.kernel.org, Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v3 4/4] kernel hacking: new config CC_OPTIMIZE_FOR_DEBUGGING
 to apply GCC -Og optimization

On Sun, Oct 28, 2018 at 10:11 PM Changbin Du <changbin.du@...il.com> wrote:
>
> This will apply GCC '-Og' optimization level which is supported
> since GCC 4.8. This optimization level offers a reasonable level
> of optimization while maintaining fast compilation and a good
> debugging experience. It is similar to '-O1' while perferring
> to keep debug ability over runtime speed.
>
> If enabling this option breaks your kernel, you should either
> disable this or find a fix (mostly in the arch code). Currently
> this option has only been tested on x86_64 and arm platform.
>
> This option can satisfy people who was searching for a method
> to disable compiler optimizations so to achieve better kernel
> debugging experience with kgdb or qemu.
>
> The main problem of '-Og' is we must not use __attribute__((error(msg))).
> The compiler will report error though the call to error function
> still can be optimize out. So we must fallback to array tricky.


I removed the sentence "So we must fallback to array tricky."

Commit 81b45683487a51b0f4d3b29d37f20d6d078544e4
killed the fallback to the negative array trick.


I also resolved a conflict.

Your series is now available in the following branch.

git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild kbuild


Please double check if I did it correctly.


--
Best Regards
Masahiro Yamada