RFD: Unwind_Backtrace for ARM EABI

[Andrew Haley <aph-gcc at littlepinkcloud dot COM>]

This is one of the last pieces in the jigsaw for gcj on ARM.

Unwind_Backtrace is not defined in the ARM exception handling spec at
http://www.arm.com/pdfs/ehabi.pdf, but it can be implemented by
performing Phase 1 of a forced unwind, calling the trace function as
we go.  This works for gcj, which uses backtraces quite heavily, and
as far as I can see it'd work everywhere else too.

Daniel Jacobowitz suggested that we probably don't want to call the
personality routine during backtraces, but I can't see that it does
any real harm and not to do so would seriously complicate things.  It
would certainly be nice to have full interoperability for backtraces,
but in my opinion that's not really essential at the present time.

Comments?

Andrew.


2007-08-08  Andrew Haley  <aph@ALL6500>

        * config/arm/libunwind.S (UNWIND_WRAPPER _Unwind_Backtrace): New.
        * config/arm/unwind-arm.h (__gnu_Unwind_Backtrace): New.
        * config/arm/unwind-arm.c (__gnu_Unwind_Backtrace): New.

Index: config/arm/libunwind.S
===================================================================
--- config/arm/libunwind.S	(revision 126979)
+++ config/arm/libunwind.S	(working copy)
@@ -237,5 +237,6 @@
 UNWIND_WRAPPER _Unwind_Resume 1
 UNWIND_WRAPPER _Unwind_Resume_or_Rethrow 1
 UNWIND_WRAPPER _Unwind_ForcedUnwind 3
+UNWIND_WRAPPER _Unwind_Backtrace 2
 
-#endif  /* __symbian__ */
+#endif  /* ndef __symbian__ */
Index: config/arm/unwind-arm.c
===================================================================
--- config/arm/unwind-arm.c	(revision 126979)
+++ config/arm/unwind-arm.c	(working copy)
@@ -950,6 +950,57 @@
 }
 
 
+/* Perform stack backtrace through unwind data.  */
+_Unwind_Reason_Code
+__gnu_Unwind_Backtrace(_Unwind_Trace_Fn trace, void * trace_argument,
+		       phase2_vrs * entry_vrs);
+_Unwind_Reason_Code
+__gnu_Unwind_Backtrace(_Unwind_Trace_Fn trace, void * trace_argument,
+		       phase2_vrs * entry_vrs)
+{
+  phase1_vrs saved_vrs;
+  _Unwind_Reason_Code code;
+
+  _Unwind_Control_Block ucb;
+  _Unwind_Control_Block *ucbp = &ucb;
+
+  /* Set the pc to the call site.  */
+  entry_vrs->core.r[R_PC] = entry_vrs->core.r[R_LR];
+
+  /* Save the core registers.  */
+  saved_vrs.core = entry_vrs->core;
+  /* Set demand-save flags.  */
+  saved_vrs.demand_save_flags = ~(_uw) 0;
+  
+  do
+    {
+      /* Find the entry for this routine.  */
+      if (get_eit_entry (ucbp, saved_vrs.core.r[R_PC]) != _URC_OK)
+	return _URC_FAILURE;
+
+      /* The dwarf unwinder assumes the context structure holds things
+	 like the function and LSDA pointers.  The ARM implementation
+	 caches these in the exception header (UCB).  To avoid
+	 rewriting everything we make the virtual IP register point at
+	 the UCB.  */
+      _Unwind_SetGR((_Unwind_Context *)&saved_vrs, 12, (_Unwind_Ptr) ucbp);
+
+      /* Call trace function.  */
+      if ((*trace) ((_Unwind_Context *) &saved_vrs, trace_argument) 
+	  != _URC_NO_REASON)
+	return _URC_FAILURE;
+
+      /* Call the pr to decide what to do.  */
+      code = ((personality_routine) UCB_PR_ADDR (ucbp))
+	(_US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND, 
+	 ucbp, (void *) &saved_vrs);
+    }
+  while (code != _URC_END_OF_STACK);
+
+  return code;
+}
+
+
 /* Common implementation for ARM ABI defined personality routines.
    ID is the index of the personality routine, other arguments are as defined
    by __aeabi_unwind_cpp_pr{0,1,2}.  */
Index: config/arm/unwind-arm.h
===================================================================
--- config/arm/unwind-arm.h	(revision 126979)
+++ config/arm/unwind-arm.h	(working copy)
@@ -205,6 +205,13 @@
 	_Unwind_Control_Block *, struct _Unwind_Context *, void *);
   _Unwind_Reason_Code _Unwind_ForcedUnwind (_Unwind_Control_Block *,
 					    _Unwind_Stop_Fn, void *);
+  /* @@@ Use unwind data to perform a stack backtrace.  The trace callback
+     is called for every stack frame in the call chain, but no cleanup
+     actions are performed.  */
+  typedef _Unwind_Reason_Code (*_Unwind_Trace_Fn) (_Unwind_Context *, void *);
+  _Unwind_Reason_Code _Unwind_Backtrace(_Unwind_Trace_Fn,
+					void*);
+
   _Unwind_Word _Unwind_GetCFA (struct _Unwind_Context *);
   void _Unwind_Complete(_Unwind_Control_Block *ucbp);
   void _Unwind_DeleteException (_Unwind_Exception *);