On Thu, Jun 9, 2022 at 1:34 AM Christophe Leroy <christophe.leroy@xxxxxxxxxx> wrote: > > > > Le 08/06/2022 à 18:12, Song Liu a écrit : > > 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). > > When CONFIG_ARCH_WANTS_MODULES_DATA_IN_VMALLOC, module code uses > module_alloc() for text and vmalloc() for data, see function > move_module() in kernel/module/main.c Thanks for the pointer! I will play with it. Song
