con [off-list ref], Masahiro Yamada [off-list ref], Jarkko Sakkinen [off-list ref], Sami Tolvanen [off-list ref], "Naveen N. Rao" [off-list ref], Marco Elver [off-list ref], Kees Cook [off-list ref], Steven Rostedt [off-list ref], Nathan Chancellor [off-list ref], "Russell King \(Oracle\)" [off-list ref], Mark Brown [off-list ref], Borislav Petkov [off-list ref], Alexander Egorenkov [off-list ref], Thomas Bogendoerfer [off-list ref], Parisc List [off-list ref], Nathaniel McCallum [off-list ref], Dmitry Torokhov [off-list ref], "David S. Miller" [off-list ref], "Kirill A. Shutemov" [off-list ref], Tobias Huschle [off-list ref], "Peter Zijlstra \(Intel\)" [off-list ref], "H. Peter Anvin" [off-list ref], sparclinux [off-list ref], Tiezhu Yang [off-list ref], Miroslav Benes <
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Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Sender: "Linuxppc-dev" [off-list ref]

On Thu, Jun 9, 2022 at 1:34 AM Christophe Leroy
[off-list ref] wrote:

Le 08/06/2022 à 18:12, Song Liu a écrit :

quoted

On Wed, Jun 8, 2022 at 7:21 AM Masami Hiramatsu [off-list ref] wrote:

quoted

Hi Jarkko,

On Wed, 8 Jun 2022 08:25:38 +0300
Jarkko Sakkinen [off-list ref] wrote:

quoted

On Wed, Jun 08, 2022 at 10:35:42AM +0800, Guo Ren wrote:

quoted

.

On Wed, Jun 8, 2022 at 8:02 AM Jarkko Sakkinen [off-list ref] wrote:

quoted

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/ (local)

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