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

Jarkko Sakkinen
2022-06-08T07:28:37Z

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