On Thu, 9 Jun 2022 15:23:16 +0200 Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > On Thu, 9 Jun 2022 at 15:14, Jarkko Sakkinen <jarkko@xxxxxxxxxx> wrote: > > > > On Wed, Jun 08, 2022 at 09:12:34AM -0700, Song Liu wrote: > > > On Wed, Jun 8, 2022 at 7:21 AM Masami Hiramatsu <mhiramat@xxxxxxxxxx> 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. > > > > > > IIUC, most users of module_alloc() use it to allocate memory for text, except > > > that module code uses it for both text and data. Therefore, I guess calling it > > > text_alloc() is not 100% accurate until we change the module code (to use > > > a different API to allocate memory for data). > > > > After reading the feedback, I'd stay on using module_alloc() because > > it has arch-specific quirks baked in. Easier to deal with them in one > > place. > > > > In that case, please ensure that you enable this only on architectures > where it is needed. arm64 implements alloc_insn_page() without relying > on module_alloc() so I would not expect to see any changes there. Hmm, what about adding CONFIG_ARCH_HAVE_ALLOC_INSN_PAGE and check it? If it is defined, kprobes will not define the __weak function, but if not, it will use module_alloc()? Thank you, -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
