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

7 files changed, 184 insertions, 62 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index b84e10fd029..c6cefe9d8e8 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -2586,9 +2586,7 @@ ada_value_assign (struct value *toval, struct value *fromval)
       write_memory_with_notification (to_addr, buffer, len);
 
       val = value_copy (toval);
-      memcpy (value_contents_raw (val).data (),
-	      value_contents (fromval).data (),
-	      TYPE_LENGTH (type));
+      copy (value_contents (fromval), value_contents_raw (val));
       deprecated_set_value_type (val, type);
 
       return val;
@@ -4184,9 +4182,7 @@ ada_convert_actual (struct value *actual, struct type *formal_type0)
 
 	      actual_type = ada_check_typedef (value_type (actual));
 	      val = allocate_value (actual_type);
-	      memcpy ((char *) value_contents_raw (val).data (),
-		      (char *) value_contents (actual).data (),
-		      TYPE_LENGTH (actual_type));
+	      copy (value_contents (actual), value_contents_raw (val));
 	      actual = ensure_lval (val);
 	    }
 	  result = value_addr (actual);
@@ -8898,7 +8894,6 @@ ada_promote_array_of_integrals (struct type *type, struct value *val)
 {
   struct type *elt_type = TYPE_TARGET_TYPE (type);
   LONGEST lo, hi;
-  struct value *res;
   LONGEST i;
 
   /* Verify that both val and type are arrays of scalars, and
@@ -8914,16 +8909,16 @@ ada_promote_array_of_integrals (struct type *type, struct value *val)
   if (!get_array_bounds (type, &lo, &hi))
     error (_("unable to determine array bounds"));
 
-  res = allocate_value (type);
+  value *res = allocate_value (type);
+  gdb::array_view<gdb_byte> res_contents = value_contents_writeable (res);
 
   /* Promote each array element.  */
   for (i = 0; i < hi - lo + 1; i++)
     {
       struct value *elt = value_cast (elt_type, value_subscript (val, lo + i));
+      int elt_len = TYPE_LENGTH (elt_type);
 
-      memcpy ((value_contents_writeable (res).data ()
-	       + (i * TYPE_LENGTH (elt_type))),
-	      value_contents_all (elt).data (), TYPE_LENGTH (elt_type));
+      copy (value_contents_all (elt), res_contents.slice (elt_len * i, elt_len));
     }
 
   return res;
diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 652161955d5..592dbe19d56 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -1037,8 +1037,8 @@ dwarf_expr_context::fetch_result (struct type *type, struct type *subobj_type,
 	    if (gdbarch_byte_order (arch) == BFD_ENDIAN_BIG)
 	      subobj_offset += n - max;
 
-	    memcpy (value_contents_raw (retval).data (),
-		    value_contents_all (val).data () + subobj_offset, len);
+	    copy (value_contents_all (val).slice (subobj_offset, len),
+		  value_contents_raw (retval));
 	  }
 	  break;
 
diff --git a/gdb/unittests/array-view-selftests.c b/gdb/unittests/array-view-selftests.c
index 9df48db3912..998bd3a5781 100644
--- a/gdb/unittests/array-view-selftests.c
+++ b/gdb/unittests/array-view-selftests.c
@@ -546,6 +546,108 @@ run_tests ()
   }
 }
 
+template <typename T>
+void
+run_copy_test ()
+{
+  /* Test non-overlapping copy.  */
+  {
+    const std::vector<T> src_v = {1, 2, 3, 4};
+    std::vector<T> dest_v (4, -1);
+
+    SELF_CHECK (dest_v != src_v);
+    copy (gdb::array_view<const T> (src_v), gdb::array_view<T> (dest_v));
+    SELF_CHECK (dest_v == src_v);
+  }
+
+  /* Test overlapping copy, where the source is before the destination.  */
+  {
+    std::vector<T> vec = {1, 2, 3, 4, 5, 6, 7, 8};
+    gdb::array_view<T> v = vec;
+
+    copy (v.slice (1, 4),
+	  v.slice (2, 4));
+
+    std::vector<T> expected = {1, 2, 2, 3, 4, 5, 7, 8};
+    SELF_CHECK (vec == expected);
+  }
+
+  /* Test overlapping copy, where the source is after the destination.  */
+  {
+    std::vector<T> vec = {1, 2, 3, 4, 5, 6, 7, 8};
+    gdb::array_view<T> v = vec;
+
+    copy (v.slice (2, 4),
+	  v.slice (1, 4));
+
+    std::vector<T> expected = {1, 3, 4, 5, 6, 6, 7, 8};
+    SELF_CHECK (vec == expected);
+  }
+
+  /* Test overlapping copy, where the source is the same as the destination.  */
+  {
+    std::vector<T> vec = {1, 2, 3, 4, 5, 6, 7, 8};
+    gdb::array_view<T> v = vec;
+
+    copy (v.slice (2, 4),
+	  v.slice (2, 4));
+
+    std::vector<T> expected = {1, 2, 3, 4, 5, 6, 7, 8};
+    SELF_CHECK (vec == expected);
+  }
+}
+
+/* Class with a non-trivial copy assignment operator, used to test the
+   array_view copy function.  */
+struct foo
+{
+  /* Can be implicitly constructed from an int, such that we can use the same
+     templated test function to test against array_view<int> and
+     array_view<foo>.  */
+  foo (int n)
+    : n (n)
+  {}
+
+  /* Needed to avoid -Wdeprecated-copy-with-user-provided-copy error with
+     Clang.  */
+  foo (const foo &other) = default;
+
+  void operator= (const foo &other)
+  {
+    this->n = other.n;
+    this->n_assign_op_called++;
+  }
+
+  bool operator==(const foo &other) const
+  {
+    return this->n == other.n;
+  }
+
+  int n;
+
+  /* Number of times the assignment operator has been called.  */
+  static int n_assign_op_called;
+};
+
+int foo::n_assign_op_called = 0;
+
+/* Test the array_view copy free function.  */
+
+static void
+run_copy_tests ()
+{
+  /* Test with a trivial type.  */
+  run_copy_test<int> ();
+
+  /* Test with a non-trivial type.  */
+  foo::n_assign_op_called = 0;
+  run_copy_test<foo> ();
+
+  /* Make sure that for the non-trivial type foo, the assignment operator was
+     called an amount of times that makes sense.  */
+  SELF_CHECK (foo::n_assign_op_called == 12);
+}
+
 } /* namespace array_view_tests */
 } /* namespace selftests */
 
@@ -555,4 +657,6 @@ _initialize_array_view_selftests ()
 {
   selftests::register_test ("array_view",
 			    selftests::array_view_tests::run_tests);
+  selftests::register_test ("array_view-copy",
+			    selftests::array_view_tests::run_copy_tests);
 }
diff --git a/gdb/valarith.c b/gdb/valarith.c
index 11acec6f167..32898f9005b 100644
--- a/gdb/valarith.c
+++ b/gdb/valarith.c
@@ -1537,7 +1537,7 @@ value_vector_widen (struct value *scalar_value, struct type *vector_type)
 {
   /* Widen the scalar to a vector.  */
   struct type *eltype, *scalar_type;
-  struct value *val, *elval;
+  struct value *elval;
   LONGEST low_bound, high_bound;
   int i;
 
@@ -1560,11 +1560,14 @@ value_vector_widen (struct value *scalar_value, struct type *vector_type)
       && !value_equal (elval, scalar_value))
     error (_("conversion of scalar to vector involves truncation"));
 
-  val = allocate_value (vector_type);
+  value *val = allocate_value (vector_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++)
     /* Duplicate the contents of elval into the destination vector.  */
-    memcpy (value_contents_writeable (val).data () + (i * TYPE_LENGTH (eltype)),
-	    value_contents_all (elval).data (), TYPE_LENGTH (eltype));
+    copy (value_contents_all (elval),
+	  val_contents.slice (i * elt_len, elt_len));
 
   return val;
 }
@@ -1575,7 +1578,6 @@ value_vector_widen (struct value *scalar_value, struct type *vector_type)
 static struct value *
 vector_binop (struct value *val1, struct value *val2, enum exp_opcode op)
 {
-  struct value *val, *tmp, *mark;
   struct type *type1, *type2, *eltype1, *eltype2;
   int t1_is_vec, t2_is_vec, elsize, i;
   LONGEST low_bound1, high_bound1, low_bound2, high_bound2;
@@ -1605,15 +1607,15 @@ vector_binop (struct value *val1, struct value *val2, enum exp_opcode op)
       || low_bound1 != low_bound2 || high_bound1 != high_bound2)
     error (_("Cannot perform operation on vectors with different types"));
 
-  val = allocate_value (type1);
-  mark = value_mark ();
+  value *val = allocate_value (type1);
+  gdb::array_view<gdb_byte> val_contents = value_contents_writeable (val);
+  value *mark = value_mark ();
   for (i = 0; i < high_bound1 - low_bound1 + 1; i++)
     {
-      tmp = value_binop (value_subscript (val1, i),
-			 value_subscript (val2, i), op);
-      memcpy (value_contents_writeable (val).data () + i * elsize,
-	      value_contents_all (tmp).data (),
-	      elsize);
+      value *tmp = value_binop (value_subscript (val1, i),
+				value_subscript (val2, i), op);
+      copy (value_contents_all (tmp),
+	    val_contents.slice (i * elsize, elsize));
      }
   value_free_to_mark (mark);
 
@@ -1894,7 +1896,7 @@ value_neg (struct value *arg1)
     return value_binop (value_zero (type, not_lval), arg1, BINOP_SUB);
   else if (type->code () == TYPE_CODE_ARRAY && type->is_vector ())
     {
-      struct value *tmp, *val = allocate_value (type);
+      struct value *val = allocate_value (type);
       struct type *eltype = check_typedef (TYPE_TARGET_TYPE (type));
       int i;
       LONGEST low_bound, high_bound;
@@ -1902,12 +1904,14 @@ value_neg (struct value *arg1)
       if (!get_array_bounds (type, &low_bound, &high_bound))
 	error (_("Could not determine the vector bounds"));
 
+      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_neg (value_subscript (arg1, i));
-	  memcpy ((value_contents_writeable (val).data ()
-		   + i * TYPE_LENGTH (eltype)),
-		  value_contents_all (tmp).data (), TYPE_LENGTH (eltype));
+	  value *tmp = value_neg (value_subscript (arg1, i));
+	  copy (value_contents_all (tmp),
+		val_contents.slice (i * elt_len, elt_len));
 	}
       return val;
     }
@@ -1937,7 +1941,6 @@ value_complement (struct value *arg1)
     val = value_from_longest (type, ~value_as_long (arg1));
   else if (type->code () == TYPE_CODE_ARRAY && type->is_vector ())
     {
-      struct value *tmp;
       struct type *eltype = check_typedef (TYPE_TARGET_TYPE (type));
       int i;
       LONGEST low_bound, high_bound;
@@ -1946,12 +1949,14 @@ value_complement (struct value *arg1)
 	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_complement (value_subscript (arg1, i));
-	  memcpy ((value_contents_writeable (val).data ()
-		   + i * TYPE_LENGTH (eltype)),
-		  value_contents_all (tmp).data (), TYPE_LENGTH (eltype));
+	  value *tmp = value_complement (value_subscript (arg1, i));
+	  copy (value_contents_all (tmp),
+		val_contents.slice (i * elt_len, elt_len));
 	}
     }
   else if (type->code () == TYPE_CODE_COMPLEX)
diff --git a/gdb/valops.c b/gdb/valops.c
index c552e828a94..ca71c128de9 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);
     }
diff --git a/gdb/value.c b/gdb/value.c
index 7649b029f91..4e66329e82c 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1344,9 +1344,13 @@ value_contents_copy_raw (struct value *dst, LONGEST dst_offset,
 					     TARGET_CHAR_BIT * length));
 
   /* Copy the data.  */
-  memcpy (value_contents_all_raw (dst).data () + dst_offset * unit_size,
-	  value_contents_all_raw (src).data () + src_offset * unit_size,
-	  length * unit_size);
+  gdb::array_view<gdb_byte> dst_contents
+    = value_contents_all_raw (dst).slice (dst_offset * unit_size,
+					  length * unit_size);
+  gdb::array_view<const gdb_byte> src_contents
+    = value_contents_all_raw (src).slice (src_offset * unit_size,
+					  length * unit_size);
+  copy (src_contents, dst_contents);
 
   /* Copy the meta-data, adjusted.  */
   src_bit_offset = src_offset * unit_size * HOST_CHAR_BIT;
@@ -1721,13 +1725,11 @@ value_copy (struct value *arg)
   val->stack = arg->stack;
   val->is_zero = arg->is_zero;
   val->initialized = arg->initialized;
+
   if (!value_lazy (val))
-    {
-      memcpy (value_contents_all_raw (val).data (),
-	      value_contents_all_raw (arg).data (),
-	      TYPE_LENGTH (value_enclosing_type (arg)));
+    copy (value_contents_all_raw (arg),
+	  value_contents_all_raw (val));
 
-    }
   val->unavailable = arg->unavailable;
   val->optimized_out = arg->optimized_out;
   val->parent = arg->parent;
@@ -1772,9 +1774,7 @@ value_non_lval (struct value *arg)
       struct type *enc_type = value_enclosing_type (arg);
       struct value *val = allocate_value (enc_type);
 
-      memcpy (value_contents_all_raw (val).data (),
-	      value_contents_all (arg).data (),
-	      TYPE_LENGTH (enc_type));
+      copy (value_contents_all (arg), value_contents_all_raw (val));
       val->type = arg->type;
       set_value_embedded_offset (val, value_embedded_offset (arg));
       set_value_pointed_to_offset (val, value_pointed_to_offset (arg));
diff --git a/gdbsupport/array-view.h b/gdbsupport/array-view.h
index edf66559e2d..5f1f46b16b9 100644
--- a/gdbsupport/array-view.h
+++ b/gdbsupport/array-view.h
@@ -19,6 +19,7 @@
 #define COMMON_ARRAY_VIEW_H
 
 #include "traits.h"
+#include <algorithm>
 #include <type_traits>
 
 /* An array_view is an abstraction that provides a non-owning view
@@ -206,6 +207,20 @@ private:
   size_type m_size;
 };
 
+/* Copy the contents referenced by the array view SRC to the array view DEST.
+
+   The two array views must have the same length.  */
+
+template <typename U, typename T>
+void copy (gdb::array_view<U> src, gdb::array_view<T> dest)
+{
+  gdb_assert (dest.size () == src.size ());
+  if (dest.data () < src.data ())
+    std::copy (src.begin (), src.end (), dest.begin ());
+  else if (dest.data () > src.data ())
+    std::copy_backward (src.begin (), src.end (), dest.end ());
+}
+
 /* Compare LHS and RHS for (deep) equality.  That is, whether LHS and
    RHS have the same sizes, and whether each pair of elements of LHS
    and RHS at the same position compares equal.  */