linux-kernel - Re: [PATCH RFC] kprobes: Remove MODULES dependency

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Date:   Fri, 10 Jul 2020 13:36:38 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>, Alexandre Ghiti <alex@...ti.fr>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH RFC] kprobes: Remove MODULES dependency

On Fri, Jul 10, 2020 at 11:03:44AM +0200, Peter Zijlstra wrote:
> On Fri, Jul 10, 2020 at 02:45:19AM +0300, Jarkko Sakkinen wrote:
> > Remove MODULES dependency and migrate from module_alloc to vmalloc().
> > According to Andi, the history with this dependency is that kprobes
> > originally required custom LKM's, which does not hold today anymore.
> > 
> > Right now one has to compile LKM support only to enable kprobes.  With
> > this change applied, it is somewhat easier to create custom test
> > kernel's with a proper debugging capabilities, thus making Linux more
> > developer friendly.
> > 
> > Cc: Andi Kleen <ak@...ux.intel.com>
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> 
> NAK
> 
> this patch is horrific, it sprinkles a metric ton of #ifdef and silently
> disables a lot of kprobe features (like all the opt stuff).

Perfectly nderstandable. I just drafted something quick andy dirty
together for idea's sake (and put RFC tag to state that).

The application where I use this chhange, is when I refactor large patch
set that I'm working on (namely SGX patch set in my case). I just want
squeece all the extra out from the kernel build and still have means for
instrumentation. A static kernel is very convenient for this kind of
purpose, as with EFI stub and statically linked user space you can have
a single test binary.

> How about unconditionally providing module_alloc() instead?

I believe so, yes.

Just so that I know (and learn), what did exactly disable optprobes?
Not too familiar with this part of the kernel - that's why I'm asking.
Does the module_alloc to vmalloc change disable it?

/Jarkko