Re: [PATCH] Eliminate dwarf2_frame_cache recursion (move dwarf2_tailcall_sniffer_first elsewhere)

[Pedro Alves <palves at redhat dot com>]

On 11/20/2013 06:03 PM, Pedro Alves wrote:

> But, the pain of investigating this made me want to have GDB itself
> assert that recursion never happens here.  So I wrote a patch to do
> that.  But, it triggers on current mainline, ...

This is the detection patch.  Don't know what people might think
of this.

----
Subject: Detect dwarf2_frame_cache recursion.

gdb/
2013-11-20  Pedro Alves  <palves@redhat.com>

	* dwarf2-frame.c (struct dwarf2_frame_cache)
	<building_frame_cache>: New field.
	(dwarf2_frame_cache): Detect recursion.
---

 gdb/dwarf2-frame.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/gdb/dwarf2-frame.c b/gdb/dwarf2-frame.c
index c4f8771..39eefe5 100644
--- a/gdb/dwarf2-frame.c
+++ b/gdb/dwarf2-frame.c
@@ -970,6 +970,9 @@ dwarf2_compile_cfa_to_ax (struct agent_expr *expr, struct axs_value *loc,
 
 struct dwarf2_frame_cache
 {
+  /* Detect recursive calls to dwarf2_frame_cache.  */
+  int building_frame_cache;
+
   /* DWARF Call Frame Address.  */
   CORE_ADDR cfa;

@@ -1036,7 +1039,14 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
   const gdb_byte *instr;

   if (*this_cache)
-    return *this_cache;
+    {
+      cache = (struct dwarf2_frame_cache *) *this_cache;
+
+      /* If this function was called recursively, the caller would get
+	 an incomplete frame cache to work with.  */
+      gdb_assert (!cache->building_frame_cache);
+      return cache;
+    }

   /* Allocate a new cache.  */
   cache = FRAME_OBSTACK_ZALLOC (struct dwarf2_frame_cache);
@@ -1048,6 +1058,9 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
   fs = XZALLOC (struct dwarf2_frame_state);
   old_chain = make_cleanup (dwarf2_frame_state_free, fs);

+  make_cleanup_restore_integer (&cache->building_frame_cache);
+  cache->building_frame_cache = 1;
+
   /* Unwind the PC.

      Note that if the next frame is never supposed to return (i.e. a call