Remove previous frame if an error occurs when computing frame id during unwind.

  https://sourceware.org/ml/gdb-patches/2014-05/msg00712.html

If an error is thrown during computing a frame id then the frame is left
in existence but without a valid frame id, this will trigger internal
errors if/when the frame is later visited (for example in a backtrace).

This patch catches errors raised while computing the frame id, and
arranges for the new frame, the one without a frame id, to be removed
from the linked list of frames.

gdb/ChangeLog:

	* frame.c (remove_prev_frame): New function.
	(get_prev_frame_if_no_cycle): Create / discard cleanup using
	remove_prev_frame.

gdb/testsuite/ChangeLog:

	* gdb.arch/amd64-invalid-stack-middle.S: New file.
	* gdb.arch/amd64-invalid-stack-middle.c: New file.
	* gdb.arch/amd64-invalid-stack-middle.exp: New file.
	* gdb.arch/amd64-invalid-stack-top.c: New file.
	* gdb.arch/amd64-invalid-stack-top.exp: New file.

1 files changed, 73 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.arch/amd64-invalid-stack-top.c b/gdb/testsuite/gdb.arch/amd64-invalid-stack-top.c
new file mode 100644
index 0000000..168dc55
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/amd64-invalid-stack-top.c
@@ -0,0 +1,73 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2014 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <sys/mman.h>
+#include <unistd.h>
+#include <assert.h>
+
+void *global_invalid_ptr = NULL;
+
+void
+func2 (void)
+{
+  /* Replace the current stack pointer and frame pointer with the invalid
+     pointer.  */
+  asm ("mov %0, %%rsp\n\tmov %0, %%rbp" : : "r" (global_invalid_ptr));
+
+  /* Create a label for a breakpoint.  */
+  asm (".global breakpt\nbreakpt:");
+}
+
+void
+func1 (void *ptr)
+{
+  global_invalid_ptr = ptr;
+  func2 ();
+}
+
+/* Finds and returns an invalid pointer, mmaps in a page, grabs a pointer
+   to it then unmaps the page again.  This is almost certainly "undefined"
+   behaviour, but should be good enough for this small test program.  */
+
+static void *
+make_invalid_ptr (void)
+{
+  int page_size, ans;
+  void *ptr;
+  
+  page_size = getpagesize ();
+  ptr =  mmap (0, page_size, PROT_NONE,
+	       MAP_PRIVATE | MAP_ANONYMOUS,
+	       -1, 0);
+  assert (ptr != MAP_FAILED);
+  ans = munmap (ptr, page_size);
+  assert (ans == 0);
+
+  return ptr;
+}
+
+int 
+main (void)
+{
+  void *invalid_ptr;
+
+  invalid_ptr = make_invalid_ptr ();
+  func1 (invalid_ptr);
+  
+  return 0;
+}