The ARM Thumb implementation of unw_tdep_getcontext switches to ARM
mode (".code 32"), but doesn't switch back to Thumb mode.
In gcc, this is fine (it automatically switches back to Thumb mode
at the end of an asm block), but in clang, this causes bad assembly
output (thumb instructions generated by C/C++ code later on are
interpreted as ARM mode assembly, which can't work).
Switching back to Thumb mode manually fixes clang, and is a no-op for gcc.
Define unw_tdep_context rather than using ucontext_t in order to support
systems that lack ucontext.h. Note that POSIX.1-2008 removed getcontext,
makecontext and swapcontext from its specification.
Signed-off-by: Ken Werner <ken.werner@linaro.org>
Change _UPTi_find_unwind_table to also look for the ARM specific unwind
information. Adjust the ARM unwind code to read memory using the accessor
routines.
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.
