[heads up] microblaze ftrace breakage since 60b1f578b578 "ftrace: Get the true parent ip for function tracer"

[Al Viro]

	For one thing, microblaze does *not* have kernel_stack_pointer(),
so defaults would not work there.  That leads to build breakage in
kernel/trace/trace_function.c since the commit in question.  Breakage is
trivial to reproduce - just enable FUNCTION_GRAPH_TRACER and try to
build the kernel...

	Moreover, unless I'm misreading their mcount.S, the registers saved
there are *NOT* in their pt_regs layout - the stored data is
	r15 (return address of _mcount())
	r2..r14
	r16..r31
and all of that is at r1 - 120, where r1 is the kernel stack pointer at the
time of _mcount() call.  So those defaults would be all wrong anyway.

	The last time I touched microblaze assembler had been a dozen years
ago, so I'd rather avoid trying to patch the things up there - not with
live microblaze maintainers around, TYVM...