Re: [PATCH][v4] livepatch/ppc: Enable livepatching on powerpc

Hi,

On Fri, 4 Mar 2016, Michael Ellerman wrote:

Hi Petr,

On Thu, 2016-03-03 at 17:52 +0100, Petr Mladek wrote:

quoted

From: Balbir Singh <bsingharora@gmail.com>

Changelog v4:
	1. Renamed klp_matchaddr() to klp_get_ftrace_location()
	   and used it just to convert the function address.
	2. Synced klp_write_module_reloc() with s390(); made it
	   inline, no error message, return -ENOSYS

OK.

quoted

	3. Added an error message when including
	   powerpc/include/asm/livepatch.h without HAVE_LIVEPATCH

I don't know why we want to do that, I don't see how it is helpful. It doesn't
even do what it says:

quoted

+#ifdef CONFIG_LIVEPATCH

...

quoted

+#else /* CONFIG_LIVEPATCH */
+#error Include linux/livepatch.h, not asm/livepatch.h
+#endif /* CONFIG_LIVEPATCH */

If I turn on CONFIG_LIVEPATCH then I can quite happily include asm/livepatch.h
and not get an error. So the check doesn't do what the message suggests.

Well, yes. I looked into the archives to find if there was a reason to 
even introduce it. It was not. It came up during a review process of the 
livepatching patch set somehow and we left it there. I only changed the 
error message to the mentioned one because we deemed it was better.
 

If we *really* want to prevent people from including asm/livepatch.h then it
needs to check for _LINUX_LIVEPATCH_H_. But there's no reason I can see why we
*must* prevent people from including asm/livepatch.h.

And on x86 & s390 it does:

  #else
  #error Live patching support is disabled; check CONFIG_LIVEPATCH
  #endif

Which is also not helpful AFAICS, and just likely to break the build for no
good reason.

This is the old message. See 383bf44d1a8b ("livepatch: change the error 
message in asm/livepatch.h header files").

Anyway, it really does not mean much. I'll send a patch for s390 and x86 
to remove it completely in a minute.

Thanks,
Miroslav