The intention in the test cases is to print the "instruction pointer"
value at certain places, and on ARM we will want to get the Program
Counter in these cases. IP is a scratch register, and not very
interesting.
Creating an alternate signal stack with a size of SIGSTKSZ (usually 8k) is
not enough on some targets because unw_cursor_t is bigger than that already.
Since the size of unw_cursor_t is part of the ABI the UNW_TDEP_CURSOR_LEN
can't be changed without breaking existent code. Therefore size of the
alternate signal stack has been increased to 1 MiB.
Signed-off-by: Ken Werner <ken.werner@linaro.org>
Dropping the extra frame for unw_backtrace itself using unw_step is
approximately 15% slower than skipping the frame in tdep_trace. So
drop the frame in the latter, and make the function a private
implementation detail for libunwind, not an exported interface.
Also moves unw_getcontext call back into unw_backtrace to avoid an
extra call frame in case slow_backtrace does not get inlined into
unw_backtrace.
Adds new function to perform a pure stack walk without unwinding,
functionally similar to backtrace() but accelerated by an address
attribute cache the caller maintains across calls.
