On Thu, 2016-02-25 at 10:39 +1100, Balbir Singh wrote:

On 25/02/16 01:28, Michael Ellerman wrote:

quoted

is_early_mcount_callsite() needs to detect either the two instruction or
the three instruction versions of the _mcount() sequence.

But if we're running a kernel with the two instruction sequence, we need
to be careful not to read instruction - 2, otherwise we might fall off
the front of a page and cause an oops.

While we're here convert to bool to make the return semantics clear.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Do we even need to do this anymore?

Yes. Otherwise the code in apply_relocate_add() will see a far call with no nop
slot after it to do the toc restore, and it considers that a bug (which it
usually is, except mcount is special).

As we discussed today I'm hoping we can clean this code up a bit more in the
medium term, but this works for now.

cheers