[libunwind] Fix unw_get_proc_info sometimes returning stale data

[Amanieu]

Summary

If unwind info is not available at the current IP, unw_get_proc_info should return a zero-filled structure rather than the info of the previous IP.

This change also makes unw_get_proc_info return UNW_ENOINFO instead of UNW_ESUCCESS.

[compnerd]

Would be nice if we could have a test case for this.

[mstorsjo]

Can the runtimes repo maintainers @mclow.lists @ldionne @EricWF give this an ack aswell?

@Amanieu Do you need someone to commit this for you?

[Amanieu]

Added a test.

[Amanieu]

@mstorsjo Yes, I need someone to commit this for me.

[compnerd]

SVN r372407

libunwind/src/UnwindCursor.hpp

 
 template <typename A, typename R>
 void UnwindCursor<A, R>::getInfo(unw_proc_info_t *info) {
-  *info = _info;
+  if (_unwindInfoMissing)
+    memset(info, 0, sizeof(*info));
+  else
+    *info = _info;
 }
 
 template <typename A, typename R>

libunwind/test/libunwind_01.pass.cpp

   test2(j, k);
 }
 
+void test_no_info() {
+  unw_context_t context;
+  unw_getcontext(&context);
+
+  unw_cursor_t cursor;
+  unw_init_local(&cursor, &context);
+
+  unw_proc_info_t info;
+  int ret = unw_get_proc_info(&cursor, &info);
+  if (ret != UNW_ESUCCESS)
+    abort();
+
+  // Set the IP to an address clearly outside any function.
+  unw_set_reg(&cursor, UNW_REG_IP, (unw_word_t)&context);
+
+  ret = unw_get_proc_info(&cursor, &info);
+  if (ret != UNW_ENOINFO)
+    abort();
+}
+
 int main() {
   test1(1);
   test2(1, 2);
   test3(1, 2, 3);
+  test_no_info();
 }