linux-kernel - Re: [PATCH v5] kernel/trace: Add DISALLOW_TRACE

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Message-ID: <20200825213931.04ec7f22@oasis.local.home>
Date:   Tue, 25 Aug 2020 21:39:31 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Nicolas Boichat <drinkcat@...omium.org>
Cc:     Douglas Anderson <dianders@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        "Guilherme G. Piccoli" <gpiccoli@...onical.com>,
        Kars Mulder <kerneldev@...smulder.nl>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Will Deacon <will@...nel.org>, Yue Hu <huyue2@...ong.com>,
        linux-kbuild@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] kernel/trace: Add DISALLOW_TRACE_PRINTK make option

On Tue, 25 Aug 2020 08:38:27 +0800
Nicolas Boichat <drinkcat@...omium.org> wrote:

> This already works. I'll be honest, I'm not 100% sure why (and if
> fully intentional)...
> 
> The CFLAGS end up in 3 generated assembly files:
> # grep -R DISALLOW_TRACE_PRINTK * | grep -v ".cmd:"
> arch/x86/kernel/asm-offsets.s:# -imultiarch x86_64-linux-gnu -D
> __KERNEL__ -D DISALLOW_TRACE_PRINTK
> kernel/bounds.s:# -imultiarch x86_64-linux-gnu -D __KERNEL__ -D
> DISALLOW_TRACE_PRINTK
> scripts/mod/devicetable-offsets.s:# -D DISALLOW_TRACE_PRINTK
> (along with all *.cmd files)
> 
> and I suspect some/all of those force a complete kernel rebuild.

Yeah, I believe that the modification of CFLAGS causes a recompile of
the entire kernel.

Thanks!

-- Steve