[PATCH] Disallow non-scalars as rvalues in agent expressions

[Stan Shebs <stan@codesourcery.com>]

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Bad Stuff(tm) happens when you try to compile an agent expression that 
wants to use a non-scalar object like a struct.  (We're talking about 
the struct itself, not a pointer to it.) Now, it actually works in GDB 
to say "print (int)bigstruct" - the first 32 bits of the struct get made 
into an integer, and the rest is discarded.  While in theory the 
bytecode compiler could do likewise, and perhaps someone will make that 
happen someday (it's not as simple as taking address, struct might be 
partly in registers), in the meantime we need to prevent non-scalar 
types from triggering internal errors all over the place.  Committed to 
trunk.

Stan

2010-03-17 Stan Shebs  <stan@codesourcery.com>

    * ax-gdb.c (require_rvalue): Disallow non-scalars.


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Index: ax-gdb.c
===================================================================
RCS file: /cvs/src/src/gdb/ax-gdb.c,v
retrieving revision 1.69
diff -p -r1.69 ax-gdb.c
*** ax-gdb.c	17 Mar 2010 22:04:43 -0000	1.69
--- ax-gdb.c	18 Mar 2010 01:44:44 -0000
*************** gen_int_literal (struct agent_expr *ax, 
*** 745,750 ****
--- 745,759 ----
  static void
  require_rvalue (struct agent_expr *ax, struct axs_value *value)
  {
+   /* Only deal with scalars, structs and such may be too large
+      to fit in a stack entry.  */
+   value->type = check_typedef (value->type);
+   if (TYPE_CODE (value->type) == TYPE_CODE_ARRAY
+       || TYPE_CODE (value->type) == TYPE_CODE_STRUCT
+       || TYPE_CODE (value->type) == TYPE_CODE_UNION
+       || TYPE_CODE (value->type) == TYPE_CODE_FUNC)
+     error ("Value not scalar: cannot be an rvalue.");
+ 
    switch (value->kind)
      {
      case axs_rvalue: