[PATCH/RFC/RFA] Print in-memory struct return values

[Mark Kettenis <kettenis at chello dot nl>]

The current GDB doesn't print the return value when using `finish' for
functions return structures that are not returned in registers.  Note
that this is a regression from GDB 6.0 for many systems.  Anyway, the
attached patch provides a way to fix this, and adds the necessary
support to the i386 target.

If there are no comments, I'll check this in in a few days.  Eli, is
the doc bit OK?

Mark


Index: ChangeLog
from  Mark Kettenis  <kettenis@gnu.org>
 
	* gdbarch.sh (gdbarch_return_value_address): New method.
	* gdbarch.h, gdbarch.c: Re-generate.
	* infcmd.c (print_return_value): Use new
	gdbarch_return_value_address method if provided.
	* i386-tdep.c (i386_return_value_address): New function.
	(i386_gdbarch_init): Set return_value_address.

 
Index: infcmd.c
===================================================================
RCS file: /cvs/src/src/gdb/infcmd.c,v
retrieving revision 1.108
diff -u -p -r1.108 infcmd.c
--- infcmd.c 28 Apr 2004 16:36:25 -0000 1.108
+++ infcmd.c 7 May 2004 17:05:04 -0000
@@ -1061,9 +1061,6 @@ print_return_value (int struct_return, s
       /* The return value can be found in the inferior's registers.  */
       value = register_value_being_returned (value_type, stop_registers);
     }
-  /* FIXME: cagney/2004-01-17: When both return_value and
-     extract_returned_value_address are available, should use that to
-     find the address of and then extract the returned value.  */
   /* FIXME: 2003-09-27: When returning from a nested inferior function
      call, it's possible (with no help from the architecture vector)
      to locate and return/print a "struct return" value.  This is just
@@ -1079,11 +1076,23 @@ print_return_value (int struct_return, s
       gdb_assert (gdbarch_return_value (current_gdbarch, value_type,
 					NULL, NULL, NULL)
 		  == RETURN_VALUE_STRUCT_CONVENTION);
-      ui_out_text (uiout, "Value returned has type: ");
-      ui_out_field_string (uiout, "return-type", TYPE_NAME (value_type));
-      ui_out_text (uiout, ".");
-      ui_out_text (uiout, " Cannot determine contents\n");
-      return;
+
+      if (gdbarch_return_value_address_p (current_gdbarch))
+	{
+	  CORE_ADDR addr;
+
+	  addr = gdbarch_return_value_address (current_gdbarch,
+					       stop_registers);
+	  value = value_at (value_type, addr, NULL);
+	}
+      else
+	{
+	  ui_out_text (uiout, "Value returned has type: ");
+	  ui_out_field_string (uiout, "return-type", TYPE_NAME (value_type));
+	  ui_out_text (uiout, ".");
+	  ui_out_text (uiout, " Cannot determine contents\n");
+	  return;
+	}
     }
   else
     {
Index: gdbarch.sh
===================================================================
RCS file: /cvs/src/src/gdb/gdbarch.sh,v
retrieving revision 1.311
diff -u -p -r1.311 gdbarch.sh
--- gdbarch.sh 5 May 2004 15:42:52 -0000 1.311
+++ gdbarch.sh 7 May 2004 17:05:05 -0000
@@ -594,6 +594,8 @@ F:2:DEPRECATED_STORE_STRUCT_RETURN:void:
 
 M:::enum return_value_convention:return_value:struct type *valtype, struct regcache *regcache, void *readbuf, const void *writebuf:valtype, regcache, readbuf, writebuf
 
+M:::CORE_ADDR:return_value_address:struct regcache *regcache:regcache
+
 # The deprecated methods RETURN_VALUE_ON_STACK, EXTRACT_RETURN_VALUE,
 # STORE_RETURN_VALUE and USE_STRUCT_CONVENTION have all been folded
 # into RETURN_VALUE.
Index: i386-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/i386-tdep.c,v
retrieving revision 1.190
diff -u -p -r1.190 i386-tdep.c
--- i386-tdep.c 30 Apr 2004 21:13:58 -0000 1.190
+++ i386-tdep.c 7 May 2004 17:05:05 -0000
@@ -1373,6 +1373,20 @@ i386_return_value (struct gdbarch *gdbar
 
   return RETURN_VALUE_REGISTER_CONVENTION;
 }
+
+/* Return the address where the return value can be found for
+   functions that use the REGISTER_VALUE_STRUCT_RETURN convention.
+   REGCACHE contains a copy of the registers from the just returned
+   function.  */
+
+static CORE_ADDR
+i386_return_value_address (struct gdbarch *gdbarch, struct regcache *regcache)
+{
+  ULONGEST addr;
+
+  regcache_cooked_read_unsigned (regcache, I386_EAX_REGNUM, &addr);
+  return addr;
+}
 
 
 /* Return the GDB type object for the "standard" data type of data in
@@ -2041,6 +2055,7 @@ i386_gdbarch_init (struct gdbarch_info i
   set_gdbarch_value_to_register (gdbarch, i386_value_to_register);
 
   set_gdbarch_return_value (gdbarch, i386_return_value);
+  set_gdbarch_return_value_address (gdbarch, i386_return_value_address);
 
   set_gdbarch_skip_prologue (gdbarch, i386_skip_prologue);
 
Index: doc/ChangeLog
from  Mark Kettenis  <kettenis@gnu.org>

	* gdbint.texinfo (Target Architecture Definition): Document
	gdbarch_return_value_address.

Index: doc/gdbint.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdbint.texinfo,v
retrieving revision 1.198
diff -u -p -r1.198 gdbint.texinfo
--- doc/gdbint.texinfo 1 May 2004 16:52:30 -0000 1.198
+++ doc/gdbint.texinfo 7 May 2004 17:05:07 -0000
@@ -3786,6 +3786,16 @@ to the inner most frame.  While replacin
 @code{struct frame_info} @var{frame} parameter would remove that
 limitation there has yet to be a demonstrated need for such a change.}
 
+@item CORE_ADDR gdbarch_return_value_address (struct gdbarch *@var{gdbarch}, struct regcache *@var{regcache})
+@findex gdbarch_return_value_address
+@anchor{gdbarch_return_value_address} Return the address where the
+return value can be found for functions that use the
+@code{RETURN_VALUE_STRUCT_CONVENTION} return-value convention
+(@pxref{gdbarch_return_value}).  A copy of the registers from the just
+returned function can be found in @var{regcache}.  @emph{This method
+should only be provided if the address of the return value can be found
+reliably from the register contents upon function return.}
+
 @item SKIP_PERMANENT_BREAKPOINT
 @findex SKIP_PERMANENT_BREAKPOINT
 Advance the inferior's PC past a permanent breakpoint.  @value{GDBN} normally