On Thu, Mar 18, 2021 at 11:13:08AM -0500, Josh Poimboeuf wrote:
> On Thu, Mar 18, 2021 at 12:31:59PM +0100, Peter Zijlstra wrote:
> > if (!kernel_text_address((unsigned long)site_addr)) {
> > - WARN_ONCE(1, "can't patch static call site at
> > %pS",
> > + /*
> > + * This skips patching __exit, which is part of
This skips patching built-in __exit, ...
?
> > + * init_section_contains() but is not part of
> > + * kernel_text_address().
> > + *
> > + * Skipping __exit is fine since it will never
+ built-in, again
> > + * be executed.
> > + */
> > + WARN_ONCE(!static_call_is_init(site),
> > + "can't patch static call site at %pS",
> > site_addr);
> > continue;
> > }
>
> It might be good to clarify the situation for __exit in modules in the
> comment and/or changelog, as they both seem to be implicitly talking
> only about __exit in vmlinux.
Correct.
> For CONFIG_MODULE_UNLOAD, the code ends up in the normal text area, so
> static_call_is_init() is false and kernel_text_address() is true.
>
> For !CONFIG_MODULE_UNLOAD, the code gets discarded during module load,
> so static_call_is_init() and kernel_text_address() are both false. I
> guess that will trigger a warning?
Oh gawd, more variants.
Afaict MODULE_UNLOAD, by virtue of that #ifdef in
rewrite_section_headers() won't even load the .exit sections. Afaict
that will break: alterative, jump_label and static_call patching all in
one go.
