When libunwind is built for a ppc32 target, for example the yocto distro
for qemuppc, and configured with options --enable-debug-frame and
--enable-debug, then the shortfall in the size of the 'opaque' member
of the unw_cursor_t type throws an assert in mi_init().
The calculations for the ppc32 target size of UNW_TDEP_CURSOR_LEN in
the comment block based on the register count plus overhead sum to 280
words. However, that value is not reflected in the ppc32 header, which
defines the size as 200. Fixing the ppc32 header value to 280 makes the
unw_cursor_t type larger than struct cursor type and the assert tests
true at run-time in mi_init().
Signed-off-by Dave Lerner <dave.lerner@windriver.com>
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.
