Trying to figure out the best value for DWARF_ARCH_UNWIND_OFFSET is
tricky at best. Various things can change the size (and offset from the
beginning of the function) of the prologue. Notably, turning on ftrace
adds calls to mcount at the beginning of functions, thereby pushing the
prologue further into the function.

So replace DWARF_ARCH_UNWIND_OFFSET with some code that continues to
execute CFA instructions until the value of return address register is
defined. This is safe to do because we know that the return address must
have been pushed onto the frame before our first function call; we just
can't figure out where at compile-time.
Signed-off-by: NMatt Fleming <matt@console-pimps.org>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

The destination address might be unaligned, so set it with
put_unaligned() for safety. This restores the previous behaviour, albeit
through the proper API.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

This was using internal symbols for unaligned accesses, bypassing the
exposed interface for variable sized safe accesses. This converts all of
the __get_unaligned_cpuXX() users over to get_unaligned() directly,
relying on the cast to select the proper internal routine.

Additionally, the __put_unaligned_cpuXX() case is superfluous given that
the destination address is aligned in all of the current cases, so just
drop that outright.

Furthermore, this switches to the asm/unaligned.h header instead of the
asm-generic version, which was silently bypassing the SH-4A optimized
unaligned ops.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

This is a first cut at a generic DWARF unwinder for the kernel. It's
still lacking DWARF64 support and the DWARF expression support hasn't
been tested very well but it is generating proper stacktraces on SH for
WARN_ON() and NULL dereferences.
Signed-off-by: NMatt Fleming <matt@console-pimps.org>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>