This is a fix to allow correctly unwinding signal frames on ARM EABI, e.g. as
result of throwing an exception.  Note that catching such exceptions is only
reliably possible if:
1. you compile with -fnon-call-exceptions, and
2. the signal is synchronous (e.g. SIGSEGV)

The v1 signal frame format (kernels 2.6.16 and 2.6.17) isn't supported.

Usage:
  make unwind_sigreturn.o
and link the resulting object into your application or library.


To verify the code is working properly in your environment, build and run the test/demo:
  make check
The expected output is something like this:
  backtrace in segv...
  ./test(_Z9backtracev+0xd)[0x458f72]
  ./test(_Z17backtrace_handleri+0xb)[0x458f98]
  ./test(+0x132a)[0x45932a]
  ./test(_Z9test_segvf+0x11)[0x458fc6]
  ./test(_Z3barj+0x13)[0x459048]
  ./test(_Z3fooj+0x5)[0x45902e]
  ./test(_Z3barj+0x9)[0x45903e]
  ./test(_Z3fooj+0x5)[0x45902e]
  ./test(_Z3barj+0x9)[0x45903e]
  ./test(_Z3fooj+0x5)[0x45902e]
  ./test(_Z3barj+0x9)[0x45903e]
  ./test(_Z3fooj+0x5)[0x45902e]
  ./test(main+0x10f)[0x459160]
  /lib/arm-linux-gnueabihf/libc.so.6(__libc_start_main+0x97)[0xb6cddaac]
  ok

  via return (no siginfo)... ok
  via return (with siginfo)... ok
  via exception (no siginfo)... ok
  via exception (with siginfo)... ok

  uncaught exception:
  ./test(_Z9backtracev+0xd)[0x458f72]
  ./test(_Z15abort_backtracev+0x5)[0x458f86]
  /usr/lib/arm-linux-gnueabihf/libstdc++.so.6(+0x7c174)[0xb6e64174]

  All tests passed