gdb: Migrate frame unwinders to use C++ classes

Frame unwinders have historically been a structure populated with
callback pointers, so that architectures (or other specific unwinders)
could install their own way to handle the inferior. However, since
moving to C++, we could use polymorphism to get the same functionality
in a more readable way. Polymorphism also makes it simpler to add new
functionality to all frame unwinders, since all that's required is
adding it to the base class.

As part of the changes to add support to disabling frame unwinders,
this commit makes the first baby step in  using polymorphism for the
frame unwinders, by making frame_unwind a virtual class, and adds a
couple of new classes. The main class added is frame_unwind_legacy,
which works the same as the previous structs, using function pointers
as callbacks. This class was added to allow the transition to happen
piecemeal. New unwinders should instead follow the lead of the other
classes implemented.

2 of the others, frame_unwind_python and frame_unwind_trampoline, were added
because it seemed simpler at the moment to do that instead of reworking
the dynamic allocation to work with the legacy class, and can be used as
an example to future implementations.

Finally, the cygwin unwinder was converted to a class since it was most
of the way there already.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Approved-By: Simon Marchi <simon.marchi@efficios.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>

1 files changed, 48 insertions, 23 deletions

diff --git a/gdb/tramp-frame.c b/gdb/tramp-frame.c
index 6368f67..9353cf6 100644
--- a/gdb/tramp-frame.c
+++ b/gdb/tramp-frame.c
@@ -57,10 +57,41 @@ tramp_frame_cache (const frame_info_ptr &this_frame,
   return tramp_cache->trad_cache;
 }
 
-static void
-tramp_frame_this_id (const frame_info_ptr &this_frame,
-		     void **this_cache,
-		     struct frame_id *this_id)
+class frame_unwind_trampoline : public frame_unwind
+{
+public:
+  frame_unwind_trampoline (enum frame_type type, const struct frame_data *data,
+			   frame_prev_arch_ftype *prev_arch_func)
+    : frame_unwind ("trampoline", type, FRAME_UNWIND_GDB, data),
+      m_prev_arch (prev_arch_func)
+  { }
+
+  int sniff (const frame_info_ptr &this_frame,
+	     void **this_prologue_cache) const override;
+
+  void this_id (const frame_info_ptr &this_frame, void **this_prologue_cache,
+		struct frame_id *id) const override;
+
+  value *prev_register (const frame_info_ptr &this_frame,
+			void **this_prologue_cache,
+			int regnum) const override;
+
+  struct gdbarch *prev_arch (const frame_info_ptr &this_frame,
+			     void **this_prologue_cache) const override
+  {
+    if (m_prev_arch == nullptr)
+      return frame_unwind::prev_arch (this_frame, this_prologue_cache);
+    return m_prev_arch (this_frame, this_prologue_cache);
+  }
+
+private:
+  frame_prev_arch_ftype *m_prev_arch;
+};
+
+void
+frame_unwind_trampoline::this_id (const frame_info_ptr &this_frame,
+				  void **this_cache,
+				  struct frame_id *this_id) const
 {
   struct trad_frame_cache *trad_cache
     = tramp_frame_cache (this_frame, this_cache);
@@ -68,10 +99,10 @@ tramp_frame_this_id (const frame_info_ptr &this_frame,
   trad_frame_get_id (trad_cache, this_id);
 }
 
-static struct value *
-tramp_frame_prev_register (const frame_info_ptr &this_frame,
-			   void **this_cache,
-			   int prev_regnum)
+struct value *
+frame_unwind_trampoline::prev_register (const frame_info_ptr &this_frame,
+					void **this_cache,
+					int prev_regnum) const
 {
   struct trad_frame_cache *trad_cache
     = tramp_frame_cache (this_frame, this_cache);
@@ -119,12 +150,11 @@ tramp_frame_start (const struct tramp_frame *tramp,
   return 0;
 }
 
-static int
-tramp_frame_sniffer (const struct frame_unwind *self,
-		     const frame_info_ptr &this_frame,
-		     void **this_cache)
+int
+frame_unwind_trampoline::sniff (const frame_info_ptr &this_frame,
+				void **this_cache) const
 {
-  const struct tramp_frame *tramp = self->unwind_data->tramp_frame;
+  const struct tramp_frame *tramp = unwind_data ()->tramp_frame;
   CORE_ADDR pc = get_frame_pc (this_frame);
   CORE_ADDR func;
   struct tramp_frame_cache *tramp_cache;
@@ -161,16 +191,11 @@ tramp_frame_prepend_unwinder (struct gdbarch *gdbarch,
   gdb_assert (tramp_frame->insn_size <= sizeof (tramp_frame->insn[0].bytes));
 
   data = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct frame_data);
-  unwinder = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct frame_unwind);
-
   data->tramp_frame = tramp_frame;
-  unwinder->type = tramp_frame->frame_type;
-  unwinder->unwind_data = data;
-  unwinder->unwinder_class = FRAME_UNWIND_GDB;
-  unwinder->sniffer = tramp_frame_sniffer;
-  unwinder->stop_reason = default_frame_unwind_stop_reason;
-  unwinder->this_id = tramp_frame_this_id;
-  unwinder->prev_register = tramp_frame_prev_register;
-  unwinder->prev_arch = tramp_frame->prev_arch;
+
+  unwinder = obstack_new <frame_unwind_trampoline> (gdbarch_obstack (gdbarch),
+						    tramp_frame->frame_type,
+						    data,
+						    tramp_frame->prev_arch);
   frame_unwind_prepend_unwinder (gdbarch, unwinder);
 }