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Date:   Wed, 8 Jun 2022 08:25:38 +0300
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     Guo Ren <guoren@kernel.org>
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Subject: Re: [PATCH] kprobes: Enable tracing for mololithic kernel images
Message-ID: <YqAy0qjI4Lktk/uJ@iki.fi>
References: <20220608000014.3054333-1-jarkko@profian.com>
 <CAJF2gTQgCn2CyZ4+VBqEEBT2b4+1KxoEXxrd+Ritk=58+U8EFA@mail.gmail.com>
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On Wed, Jun 08, 2022 at 10:35:42AM +0800, Guo Ren wrote:
> .
> 
> On Wed, Jun 8, 2022 at 8:02 AM Jarkko Sakkinen <jarkko@profian.com> wrote:
> >
> > Tracing with kprobes while running a monolithic kernel is currently
> > impossible because CONFIG_KPROBES is dependent of CONFIG_MODULES.  This
> > dependency is a result of kprobes code using the module allocator for the
> > trampoline code.
> >
> > Detaching kprobes from modules helps to squeeze down the user space,
> > e.g. when developing new core kernel features, while still having all
> > the nice tracing capabilities.
> >
> > For kernel/ and arch/*, move module_alloc() and module_memfree() to
> > module_alloc.c, and compile as part of vmlinux when either CONFIG_MODULES
> > or CONFIG_KPROBES is enabled.  In addition, flag kernel module specific
> > code with CONFIG_MODULES.
> >
> > As the result, kprobes can be used with a monolithic kernel.
> It's strange when MODULES is n, but vmlinux still obtains module_alloc.
> 
> Maybe we need a kprobe_alloc, right?

Perhaps not the best name but at least it documents the fact that
they use the same allocator.

Few years ago I carved up something "half-way there" for kprobes,
and I used the name text_alloc() [*].

[*] https://lore.kernel.org/all/20200724050553.1724168-1-jarkko.sakkinen@linux.intel.com/ 

BR, Jarkko