gdb: change functions returning value contents to use gdb::array_view

The bug fixed by this [1] patch was caused by an out-of-bounds access to
a value's content.  The code gets the value's content (just a pointer)
and then indexes it with a non-sensical index.

This made me think of changing functions that return value contents to
return array_views instead of a plain pointer.  This has the advantage
that when GDB is built with _GLIBCXX_DEBUG, accesses to the array_view
are checked, making bugs more apparent / easier to find.

This patch changes the return types of these functions, and updates
callers to call .data() on the result, meaning it's not changing
anything in practice.  Additional work will be needed (which can be done
little by little) to make callers propagate the use of array_view and
reap the benefits.

[1] https://sourceware.org/pipermail/gdb-patches/2021-September/182306.html

Change-Id: I5151f888f169e1c36abe2cbc57620110673816f3

1 files changed, 14 insertions, 17 deletions

diff --git a/gdb/f-lang.c b/gdb/f-lang.c
index 16ec9e0..1b5a99c 100644
--- a/gdb/f-lang.c
+++ b/gdb/f-lang.c
@@ -770,7 +770,7 @@ eval_op_f_abs (struct type *expect_type, struct expression *exp,
     case TYPE_CODE_FLT:
       {
 	double d
-	  = fabs (target_float_to_host_double (value_contents (arg1),
+	  = fabs (target_float_to_host_double (value_contents (arg1).data (),
 					       value_type (arg1)));
 	return value_from_host_double (type, d);
       }
@@ -800,10 +800,10 @@ eval_op_f_mod (struct type *expect_type, struct expression *exp,
     case TYPE_CODE_FLT:
       {
 	double d1
-	  = target_float_to_host_double (value_contents (arg1),
+	  = target_float_to_host_double (value_contents (arg1).data (),
 					 value_type (arg1));
 	double d2
-	  = target_float_to_host_double (value_contents (arg2),
+	  = target_float_to_host_double (value_contents (arg2).data (),
 					 value_type (arg2));
 	double d3 = fmod (d1, d2);
 	return value_from_host_double (type, d3);
@@ -833,7 +833,7 @@ eval_op_f_ceil (struct type *expect_type, struct expression *exp,
   if (type->code () != TYPE_CODE_FLT)
     error (_("argument to CEILING must be of type float"));
   double val
-    = target_float_to_host_double (value_contents (arg1),
+    = target_float_to_host_double (value_contents (arg1).data (),
 				   value_type (arg1));
   val = ceil (val);
   return value_from_host_double (type, val);
@@ -851,7 +851,7 @@ eval_op_f_floor (struct type *expect_type, struct expression *exp,
   if (type->code () != TYPE_CODE_FLT)
     error (_("argument to FLOOR must be of type float"));
   double val
-    = target_float_to_host_double (value_contents (arg1),
+    = target_float_to_host_double (value_contents (arg1).data (),
 				   value_type (arg1));
   val = floor (val);
   return value_from_host_double (type, val);
@@ -883,10 +883,10 @@ eval_op_f_modulo (struct type *expect_type, struct expression *exp,
     case TYPE_CODE_FLT:
       {
 	double a
-	  = target_float_to_host_double (value_contents (arg1),
+	  = target_float_to_host_double (value_contents (arg1).data (),
 					 value_type (arg1));
 	double p
-	  = target_float_to_host_double (value_contents (arg2),
+	  = target_float_to_host_double (value_contents (arg2).data (),
 					 value_type (arg2));
 	double result = fmod (a, p);
 	if (result != 0 && (a < 0.0) != (p < 0.0))
@@ -1384,11 +1384,9 @@ fortran_undetermined::value_subarray (value *array,
 	    array = value_at_lazy (array_slice_type,
 				   value_address (array) + total_offset);
 	  else
-	    array = value_from_contents_and_address (array_slice_type,
-						     (value_contents (array)
-						      + total_offset),
-						     (value_address (array)
-						      + total_offset));
+	    array = value_from_contents_and_address
+	      (array_slice_type, value_contents (array).data () + total_offset,
+	       value_address (array) + total_offset);
 	}
       else if (!value_lazy (array))
 	array = value_from_component (array, array_slice_type, total_offset);
@@ -1518,7 +1516,7 @@ fortran_structop_operation::evaluate (struct type *expect_type,
       struct type *elt_type = value_type (elt);
       if (is_dynamic_type (elt_type))
 	{
-	  const gdb_byte *valaddr = value_contents_for_printing (elt);
+	  const gdb_byte *valaddr = value_contents_for_printing (elt).data ();
 	  CORE_ADDR address = value_address (elt);
 	  gdb::array_view<const gdb_byte> view
 	    = gdb::make_array_view (valaddr, TYPE_LENGTH (elt_type));
@@ -1746,10 +1744,9 @@ fortran_argument_convert (struct value *value, bool is_artificial)
 	  const int length = TYPE_LENGTH (type);
 	  const CORE_ADDR addr
 	    = value_as_long (value_allocate_space_in_inferior (length));
-	  write_memory (addr, value_contents (value), length);
-	  struct value *val
-	    = value_from_contents_and_address (type, value_contents (value),
-					       addr);
+	  write_memory (addr, value_contents (value).data (), length);
+	  struct value *val = value_from_contents_and_address
+	    (type, value_contents (value).data (), addr);
 	  return value_addr (val);
 	}
       else