Re: [rfa] Attach vsyscall support for GNU/Linux

[Daniel Jacobowitz <drow@false.org>]

On Sun, Nov 07, 2004 at 06:35:44PM +0100, Mark Kettenis wrote:
>    Date: Fri, 5 Nov 2004 18:42:30 -0500
>    From: Daniel Jacobowitz <drow@false.org>
> 
>    How about this, in the meantime?  If you don't like the approach, I'll
>    wait until we can properly decide the relationship between unwinders
>    and frame types.
> 
>    This patch adds a new sniffer, dwarf2_signal_frame_sniffer, which will
>    only accept the frame if an architecture-specific hook has claimed that
>    this is a signal frame (i386 GNU/Linux provides one that works by
>    name).  However, we then use the CFI normally - the only difference is
>    that the result has SIGTRAMP_FRAME as its type.  It works beautifully! 
>    Tested on i386-pc-linux-gnu, with vsyscall DSO.
> 
> Within the current framework this seems to be a reasonable approach.
> Actually it's a lot less invasive than I envisioned this to be.  So,
> actually I like it ;-).  Thanks!  I'm wondering though whether we need
> the seperate dwarf2_signal_frame_sniffer.  Actually I'm sure we don't.
> Targets that don't want this simply shouldn't provide the
> signal_frame_p() function.  Can you fix that?  Just change
> dwarf2_frame_sniffer such that it checks signal_frame_p() and returns
> &dwarf2_sigtramp_frame_unwind instead of &dwarf2_frame_unwind if it's
> true.
> 
> Oh, and please check the dwarf2-frame.* changes in as a seperately
> from the vsyscall changes.

Here's this bit, as committed - let me know if I didn't get it quite
the way you wanted.  Thanks for the observation about just using one
sniffer; it looks much cleaner now.

-- 
Daniel Jacobowitz

2004-11-07  Daniel Jacobowitz  <dan@debian.org>

	* dwarf2-frame.c (struct dwarf2_frame_ops): Add signal_frame_p.
	(dwarf2_frame_set_signal_frame_p, dwarf2_frame_signal_frame_p)
	(dwarf2_signal_frame_unwind): New.
	(dwarf2_frame_sniffer): Use dwarf2_frame_signal_frame_p.
	* dwarf2-frame.h (dwarf2_frame_set_signal_frame_p): New prototype.

Index: gdb/dwarf2-frame.c
===================================================================
RCS file: /big/fsf/rsync/src-cvs/src/gdb/dwarf2-frame.c,v
retrieving revision 1.41
diff -u -p -r1.41 dwarf2-frame.c
--- gdb/dwarf2-frame.c	4 Nov 2004 21:15:15 -0000	1.41
+++ gdb/dwarf2-frame.c	7 Nov 2004 17:41:58 -0000
@@ -471,6 +471,10 @@ struct dwarf2_frame_ops
 {
   /* Pre-initialize the register state REG for register REGNUM.  */
   void (*init_reg) (struct gdbarch *, int, struct dwarf2_frame_state_reg *);
+
+  /* Check whether the frame preceding NEXT_FRAME will be a signal
+     trampoline.  */
+  int (*signal_frame_p) (struct gdbarch *, struct frame_info *);
 };
 
 /* Default architecture-specific register state initialization
@@ -547,6 +551,33 @@ dwarf2_frame_init_reg (struct gdbarch *g
 
   ops->init_reg (gdbarch, regnum, reg);
 }
+
+/* Set the architecture-specific signal trampoline recognition
+   function for GDBARCH to SIGNAL_FRAME_P.  */
+
+void
+dwarf2_frame_set_signal_frame_p (struct gdbarch *gdbarch,
+				 int (*signal_frame_p) (struct gdbarch *,
+							struct frame_info *))
+{
+  struct dwarf2_frame_ops *ops = gdbarch_data (gdbarch, dwarf2_frame_data);
+
+  ops->signal_frame_p = signal_frame_p;
+}
+
+/* Query the architecture-specific signal frame recognizer for
+   NEXT_FRAME.  */
+
+static int
+dwarf2_frame_signal_frame_p (struct gdbarch *gdbarch,
+			     struct frame_info *next_frame)
+{
+  struct dwarf2_frame_ops *ops = gdbarch_data (gdbarch, dwarf2_frame_data);
+
+  if (ops->signal_frame_p == NULL)
+    return 0;
+  return ops->signal_frame_p (gdbarch, next_frame);
+}
 \f
 
 struct dwarf2_frame_cache
@@ -841,6 +872,13 @@ static const struct frame_unwind dwarf2_
   dwarf2_frame_prev_register
 };
 
+static const struct frame_unwind dwarf2_signal_frame_unwind =
+{
+  SIGTRAMP_FRAME,
+  dwarf2_frame_this_id,
+  dwarf2_frame_prev_register
+};
+
 const struct frame_unwind *
 dwarf2_frame_sniffer (struct frame_info *next_frame)
 {
@@ -848,10 +886,18 @@ dwarf2_frame_sniffer (struct frame_info 
      function.  frame_pc_unwind(), for a no-return next function, can
      end up returning something past the end of this function's body.  */
   CORE_ADDR block_addr = frame_unwind_address_in_block (next_frame);
-  if (dwarf2_frame_find_fde (&block_addr))
-    return &dwarf2_frame_unwind;
+  if (!dwarf2_frame_find_fde (&block_addr))
+    return NULL;
 
-  return NULL;
+  /* On some targets, signal trampolines may have unwind information.
+     We need to recognize them so that we set the frame type
+     correctly.  */
+
+  if (dwarf2_frame_signal_frame_p (get_frame_arch (next_frame),
+				   next_frame))
+    return &dwarf2_signal_frame_unwind;
+
+  return &dwarf2_frame_unwind;
 }
 \f
 
Index: gdb/dwarf2-frame.h
===================================================================
RCS file: /big/fsf/rsync/src-cvs/src/gdb/dwarf2-frame.h,v
retrieving revision 1.6
diff -u -p -r1.6 dwarf2-frame.h
--- gdb/dwarf2-frame.h	28 Feb 2004 16:59:32 -0000	1.6
+++ gdb/dwarf2-frame.h	7 Nov 2004 17:40:41 -0000
@@ -79,6 +79,14 @@ extern void dwarf2_frame_set_init_reg (s
 				       void (*init_reg) (struct gdbarch *, int,
 					     struct dwarf2_frame_state_reg *));
 
+/* Set the architecture-specific signal trampoline recognition
+   function for GDBARCH to SIGNAL_FRAME_P.  */
+
+extern void
+  dwarf2_frame_set_signal_frame_p (struct gdbarch *gdbarch,
+				   int (*signal_frame_p) (struct gdbarch *,
+							  struct frame_info *));
+
 /* Return the frame unwind methods for the function that contains PC,
    or NULL if it can't be handled by DWARF CFI frame unwinder.  */