gdbsupport: add array_view copy function

An assertion was recently added to array_view::operator[] to ensure we
don't do out of bounds accesses.  However, when the array_view is copied
to or from using memcpy, it bypasses that safety.

To address this, add a `copy` free function that copies data from an
array view to another, ensuring that the destination and source array
views have the same size.  When copying to or from parts of an
array_view, we are expected to use gdb::array_view::slice, which does
its own bounds check.  With all that, any copy operation that goes out
of bounds should be caught by an assertion at runtime.

copy is implemented using std::copy and std::copy_backward, which, at
least on libstdc++, appears to pick memmove when copying trivial data.
So in the end there shouldn't be much difference vs using a bare memcpy,
as we do right now.  When copying non-trivial data, std::copy and
std::copy_backward assigns each element in a loop.

To properly support overlapping ranges, we must use std::copy or
std::copy_backward, depending on whether the destination is before the
source or vice-versa.  std::copy and std::copy_backward don't support
copying exactly overlapping ranges (where the source range is equal to
the destination range).  But in this case, no copy is needed anyway, so
we do nothing.

The order of parameters of the new copy function is based on std::copy
and std::copy_backward, where the source comes before the destination.

Change a few randomly selected spots to use the new function, to show
how it can be used.

Add a test for the new function, testing both with arrays of a trivial
type (int) and of a non-trivial type (foo).  Test non-overlapping
ranges as well as three kinds of overlapping ranges: source before dest,
dest before source, and dest == source.

Change-Id: Ibeaca04e0028410fd44ce82f72e60058d6230a03

1 files changed, 19 insertions, 16 deletions

diff --git a/gdb/valops.c b/gdb/valops.c
index c552e82..ca71c12 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -954,18 +954,19 @@ value_one (struct type *type)
       struct type *eltype = check_typedef (TYPE_TARGET_TYPE (type1));
       int i;
       LONGEST low_bound, high_bound;
-      struct value *tmp;
 
       if (!get_array_bounds (type1, &low_bound, &high_bound))
 	error (_("Could not determine the vector bounds"));
 
       val = allocate_value (type);
+      gdb::array_view<gdb_byte> val_contents = value_contents_writeable (val);
+      int elt_len = TYPE_LENGTH (eltype);
+
       for (i = 0; i < high_bound - low_bound + 1; i++)
 	{
-	  tmp = value_one (eltype);
-	  memcpy ((value_contents_writeable (val).data ()
-		   + i * TYPE_LENGTH (eltype)),
-		  value_contents_all (tmp).data (), TYPE_LENGTH (eltype));
+	  value *tmp = value_one (eltype);
+	  copy (value_contents_all (tmp),
+		val_contents.slice (i * elt_len, elt_len));
 	}
     }
   else
@@ -1342,8 +1343,7 @@ value_assign (struct value *toval, struct value *fromval)
      implies the returned value is not lazy, even if TOVAL was.  */
   val = value_copy (toval);
   set_value_lazy (val, 0);
-  memcpy (value_contents_raw (val).data (), value_contents (fromval).data (),
-	  TYPE_LENGTH (type));
+  copy (value_contents (fromval), value_contents_raw (val));
 
   /* We copy over the enclosing type and pointed-to offset from FROMVAL
      in the case of pointer types.  For object types, the enclosing type
@@ -4058,10 +4058,13 @@ value_literal_complex (struct value *arg1,
   arg1 = value_cast (real_type, arg1);
   arg2 = value_cast (real_type, arg2);
 
-  memcpy (value_contents_raw (val).data (),
-	  value_contents (arg1).data (), TYPE_LENGTH (real_type));
-  memcpy (value_contents_raw (val).data () + TYPE_LENGTH (real_type),
-	  value_contents (arg2).data (), TYPE_LENGTH (real_type));
+  int len = TYPE_LENGTH (real_type);
+
+  copy (value_contents (arg1),
+	value_contents_raw (val).slice (0, len));
+  copy (value_contents (arg2),
+	value_contents_raw (val).slice (len, len));
+
   return val;
 }
 
@@ -4102,12 +4105,12 @@ cast_into_complex (struct type *type, struct value *val)
       struct type *val_real_type = TYPE_TARGET_TYPE (value_type (val));
       struct value *re_val = allocate_value (val_real_type);
       struct value *im_val = allocate_value (val_real_type);
+      int len = TYPE_LENGTH (val_real_type);
 
-      memcpy (value_contents_raw (re_val).data (),
-	      value_contents (val).data (), TYPE_LENGTH (val_real_type));
-      memcpy (value_contents_raw (im_val).data (),
-	      value_contents (val).data () + TYPE_LENGTH (val_real_type),
-	      TYPE_LENGTH (val_real_type));
+      copy (value_contents (val).slice (0, len),
+	    value_contents_raw (re_val));
+      copy (value_contents (val).slice (len, len),
+	    value_contents_raw (im_val));
 
       return value_literal_complex (re_val, im_val, type);
     }