Re: [PATCH] kprobes: Enable tracing for mololithic kernel images

[Jarkko Sakkinen]

On Wed, Jun 08, 2022 at 11:21:15PM +0900, Masami Hiramatsu wrote:
> Hi Jarkko,
> 
> On Wed, 8 Jun 2022 08:25:38 +0300
> Jarkko Sakkinen <jarkko@xxxxxxxxxx> wrote:
> 
> > 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@xxxxxxxxxxx> 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@xxxxxxxxxxxxxxx/ 
> 
> Yeah, I remember that. Thank you for updating your patch!
> I think the idea (split module_alloc() from CONFIG_MODULE) is good to me.
> If module support maintainers think this name is not good, you may be
> able to rename it as text_alloc() and make the module_alloc() as a
> wrapper of it.
> 
> Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> for kprobe side.

Thanks a lot! 

If I split that code into its own patch with no code changes,
can I attach this to the patch? I.e. most likely I'll split
arch's into their own patches.

> Thank you,
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

BR, Jarkko