[PATCH] dwarf2: Fix dwarf stack fetch array view size mismatch

[Denis Lukianov <denis@voxelsoft.com>]

Following change 4bce7cdaf4 "gdbsupport: add array_view copy function",
dwarf stack fetch sometimes cause an internal-error in
array_view::copy, where a gdb_assert expects the source and destination
view sizes to match. When called from dwarf_expr_context::fetch_result
sometimes the lengths don't match.

Both the source and destination views each have a separate implicit
length. The source is correctly sliced for the copy. However, the
destination is passed with the full allocated length, which does not
necessarily match the source length.

This patch slices the destination to match the source length.

diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 3549745df04..aa203e87bfb 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -1025,7 +1025,7 @@ dwarf_expr_context::fetch_result (struct type
*type, struct type *subobj_type,
              subobj_offset += n - max;
 
            copy (value_contents_all (val).slice (subobj_offset, len),
-                 value_contents_raw (retval));
+                 value_contents_raw (retval).slice (0, len));
          }
          break;