Re: [PATCH 2/2] handle VLA in a struct or union

[pinskia at gmail dot com]

> On May 8, 2014, at 11:46 AM, Tom Tromey <tromey@redhat.com> wrote:
> 
> It is valid in C to have a VLA in a struct or union type, but gdb did
> not handle this.

In GNU C only. It is extension.

Thanks,
Andrew

> 
> This patch adds support for these cases in the obvious way.
> 
> Built and regtested on x86-64 Fedora 20.
> New tests included.
> 
> However, before this goes in, I'd like to understand the oddity
> pointed out by a change in is_dynamic_type.  That is, this test:
> 
>          /* This can happen with Ada for reasons unknown.  */
>          && TYPE_FIELD_TYPE (type, i) != NULL
> 
> is needed to avoid a crash with the Ada "iwide.exp" test.  This type:
> 
>    (top-gdb) p real_type.main_type.name
>    $15 = 0x7ffff0354c6d "ada__tags__type_specific_data___XVE"
> 
> ... has a seemingly invalid field:
> 
>    (top-gdb) p real_type.main_type.nfields
>    $9 = 13
> [...]
>    (top-gdb) p real_type.main_type.flds_bnds.fields[12]
>    $12 = {
>      loc = {
>    bitpos = 576,
>    enumval = 576,
>    physaddr = 576,
>    physname = 0x240 <Address 0x240 out of bounds>,
>    dwarf_block = 0x240
>      },
>      artificial = 0,
>      loc_kind = FIELD_LOC_KIND_BITPOS,
>      bitsize = 0,
>      type = 0x0,
>      name = 0x0
>    }
> 
> Joel, can you comment?  Thanks.
> 
> 2014-05-08  Tom Tromey  <tromey@redhat.com>
> 
>    * gdbtypes.c (is_dynamic_type, resolve_dynamic_type)
>    <TYPE_CODE_STRUCT, TYPE_CODE_UNION>: New cases.
> 
> 2014-05-08  Tom Tromey  <tromey@redhat.com>
> 
>    * gdb.base/vla-datatypes.exp: Add tests for VLA-in-structure and
>    VLA-in-union.
>    * gdb.base/vla-datatypes.c (vla_factory): Add vla_struct,
>    vla_union types.  Initialize objects of those types and compute
>    their sizes.
> ---
> gdb/ChangeLog                            |  5 ++
> gdb/gdbtypes.c                           | 94 ++++++++++++++++++++++++++++++++
> gdb/testsuite/ChangeLog                  |  8 +++
> gdb/testsuite/gdb.base/vla-datatypes.c   | 16 ++++++
> gdb/testsuite/gdb.base/vla-datatypes.exp | 14 +++++
> 5 files changed, 137 insertions(+)
> 
> diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
> index 95b861e..59f354a 100644
> --- a/gdb/gdbtypes.c
> +++ b/gdb/gdbtypes.c
> @@ -1636,6 +1636,20 @@ is_dynamic_type (struct type *type)
>      return 1;
>    return is_dynamic_type (TYPE_TARGET_TYPE (type));
>       }
> +
> +    case TYPE_CODE_STRUCT:
> +    case TYPE_CODE_UNION:
> +      {
> +    int i;
> +
> +    for (i = 0; i < TYPE_NFIELDS (type); ++i)
> +      if (!field_is_static (&TYPE_FIELD (type, i))
> +          /* This can happen with Ada for reasons unknown.  */
> +          && TYPE_FIELD_TYPE (type, i) != NULL
> +          && is_dynamic_type (TYPE_FIELD_TYPE (type, i)))
> +        return 1;
> +      }
> +      break;
>     }
> 
>   return 0;
> @@ -1753,6 +1767,86 @@ resolve_dynamic_type (struct type *type, CORE_ADDR addr)
>       case TYPE_CODE_RANGE:
>    resolved_type = resolve_dynamic_range (type);
>    break;
> +
> +    case TYPE_CODE_UNION:
> +      {
> +    int i;
> +    unsigned int max_len;
> +
> +    resolved_type = copy_type (type);
> +    TYPE_FIELDS (resolved_type)
> +      = TYPE_ALLOC (resolved_type,
> +            TYPE_NFIELDS (resolved_type) * sizeof (struct field));
> +    memcpy (TYPE_FIELDS (resolved_type),
> +        TYPE_FIELDS (type),
> +        TYPE_NFIELDS (resolved_type) * sizeof (struct field));
> +    for (i = 0; i < TYPE_NFIELDS (resolved_type); ++i)
> +      {
> +        struct type *t;
> +
> +        if (field_is_static (&TYPE_FIELD (type, i)))
> +          continue;
> +
> +        t = resolve_dynamic_type (TYPE_FIELD_TYPE (resolved_type, i),
> +                      addr);
> +
> +        TYPE_FIELD_TYPE (resolved_type, i) = t;
> +        if (TYPE_LENGTH (t) > max_len)
> +          max_len = TYPE_LENGTH (t);
> +      }
> +
> +    TYPE_LENGTH (resolved_type) = max_len;
> +      }
> +      break;
> +
> +    case TYPE_CODE_STRUCT:
> +      {
> +    int i;
> +    int vla_field = TYPE_NFIELDS (type) - 1;
> +
> +    resolved_type = copy_type (type);
> +    TYPE_FIELDS (resolved_type)
> +      = TYPE_ALLOC (resolved_type,
> +            TYPE_NFIELDS (resolved_type) * sizeof (struct field));
> +    memcpy (TYPE_FIELDS (resolved_type),
> +        TYPE_FIELDS (type),
> +        TYPE_NFIELDS (resolved_type) * sizeof (struct field));
> +    for (i = 0; i < TYPE_NFIELDS (resolved_type); ++i)
> +      {
> +        struct type *t;
> +
> +        if (field_is_static (&TYPE_FIELD (type, i)))
> +          continue;
> +
> +        t = resolve_dynamic_type (TYPE_FIELD_TYPE (resolved_type, i),
> +                      addr);
> +
> +        /* This is a bit odd.  We do not support a VLA in any
> +           position of a struct except for the last.  GCC does
> +           have an extension that allows a VLA in the middle of a
> +           structure, but the DWARF it emits is relatively useless
> +           to us, so we can't represent such a type properly --
> +           and even if we could, we do not have enough information
> +           to redo structure layout anyway.  Nevertheless, we
> +           check all the fields in case something odd slips
> +           through, since it's better to see an error than
> +           incorrect results.  */
> +        if (t != TYPE_FIELD_TYPE (resolved_type, i)
> +        && i != vla_field)
> +          error (_("Attempt to resolve a variably-sized type which appears "
> +               "in the interior of a structure type"));
> +
> +        TYPE_FIELD_TYPE (resolved_type, i) = t;
> +      }
> +
> +    /* Due to the above restrictions we can successfully compute
> +       the size of the resulting structure here, as the offset of
> +       the final field plus its size.  */
> +    TYPE_LENGTH (resolved_type)
> +      = (TYPE_FIELD_BITPOS (resolved_type, vla_field) / TARGET_CHAR_BIT
> +         + TYPE_LENGTH (TYPE_FIELD_TYPE (resolved_type, vla_field)));
> +      }
> +      break;
>     }
> 
>   return resolved_type;
> diff --git a/gdb/testsuite/gdb.base/vla-datatypes.c b/gdb/testsuite/gdb.base/vla-datatypes.c
> index 51e342e..8561a4e 100644
> --- a/gdb/testsuite/gdb.base/vla-datatypes.c
> +++ b/gdb/testsuite/gdb.base/vla-datatypes.c
> @@ -46,6 +46,18 @@ vla_factory (int n)
>   BAR             bar_vla[n];
>   int i;
> 
> +  struct vla_struct
> +  {
> +    int something;
> +    int vla_field[n];
> +  } vla_struct_object;
> +
> +  union vla_union
> +  {
> +    int vla_field[n];
> +  } vla_union_object;
> +
> +  vla_struct_object.something = n;
>   for (i = 0; i < n; i++)
>     {
>       int_vla[i] = i*2;
> @@ -61,6 +73,8 @@ vla_factory (int n)
>       foo_vla[i].a = i*2;
>       bar_vla[i].x = i*2;
>       bar_vla[i].y.a = i*2;
> +      vla_struct_object.vla_field[i] = i*2;
> +      vla_union_object.vla_field[i] = i*2;
>     }
> 
>   size_t int_size        = sizeof(int_vla);     /* vlas_filled */
> @@ -74,6 +88,8 @@ vla_factory (int n)
>   size_t uchar_size      = sizeof(unsigned_char_vla);
>   size_t foo_size        = sizeof(foo_vla);
>   size_t bar_size        = sizeof(bar_vla);
> +  size_t vla_struct_object_size = sizeof(vla_struct_object);
> +  size_t vla_union_object_size = sizeof(vla_union_object);
> 
>   return;                                 /* break_end_of_vla_factory */
> }
> diff --git a/gdb/testsuite/gdb.base/vla-datatypes.exp b/gdb/testsuite/gdb.base/vla-datatypes.exp
> index 8247658..36af38d 100644
> --- a/gdb/testsuite/gdb.base/vla-datatypes.exp
> +++ b/gdb/testsuite/gdb.base/vla-datatypes.exp
> @@ -53,6 +53,10 @@ gdb_test "print foo_vla" \
> gdb_test "print bar_vla" \
>          "\\\{\\\{x = 0, y = \\\{a = 0\\\}\\\}, \\\{x = 2, y = \\\{a = 2\\\}\\\}, \\\{x = 4, y = \\\{a = 4\\\}\\\}, \\\{x = 6, y = \\\{a = 6\\\}\\\}, \\\{x = 8, y = \\\{a = 8\\\}\\\}\\\}" \
>          "print bar_vla"
> +gdb_test "print vla_struct_object" \
> +    "\\\{something = 5, vla_field = \\\{0, 2, 4, 6, 8\\\}\\\}"
> +gdb_test "print vla_union_object" \
> +    "\\\{vla_field = \\\{0, 2, 4, 6, 8\\\}\\\}"
> 
> # Check whatis of VLA's.
> gdb_test "whatis int_vla" "type = int \\\[5\\\]" "whatis int_vla"
> @@ -74,6 +78,8 @@ gdb_test "whatis unsigned_char_vla" "type = unsigned char \\\[5\\\]" \
>          "whatis unsigned_char_vla"
> gdb_test "whatis foo_vla" "type = struct foo \\\[5\\\]" "whatis foo_vla"
> gdb_test "whatis bar_vla" "type = BAR \\\[5\\\]" "whatis bar_vla"
> +gdb_test "whatis vla_struct_object" "type = struct vla_struct"
> +gdb_test "whatis vla_union_object" "type = union vla_union"
> 
> # Check ptype of VLA's.
> gdb_test "ptype int_vla" "type = int \\\[5\\\]" "ptype int_vla"
> @@ -96,6 +102,10 @@ gdb_test "ptype foo_vla" "type = struct foo {\r\n\\s+int a;\r\n} \\\[5\\\]" \
> gdb_test "ptype bar_vla" \
>          "type = struct bar {\r\n\\s+int x;\r\n\\s+struct foo y;\r\n} \\\[5\\\]" \
>          "ptype bar_vla"
> +gdb_test "ptype vla_struct_object" \
> +    "type = struct vla_struct {\r\n\\s+int something;\r\n\\s+int vla_field\\\[5\\\];\r\n}"
> +gdb_test "ptype vla_union_object" \
> +    "type = union vla_union {\r\n\\s+int vla_field\\\[5\\\];\r\n}"
> 
> # Check the size of the VLA's.
> gdb_breakpoint [gdb_get_line_number "break_end_of_vla_factory"]
> @@ -119,6 +129,10 @@ gdb_test "print uchar_size == sizeof(unsigned_char_vla)" " = 1" \
>          "size of unsigned_char_vla"
> gdb_test "print foo_size == sizeof(foo_vla)" " = 1" "size of foo_vla"
> gdb_test "print bar_size == sizeof(bar_vla)" " = 1" "size of bar_vla"
> +gdb_test "print vla_struct_object_size == sizeof(vla_struct_object)" \
> +    " = 1" "size of vla_struct_object"
> +gdb_test "print vla_union_object_size == sizeof(vla_union_object)" \
> +    " = 1" "size of vla_union_object"
> 
> # Check side effects for sizeof argument.
> set sizeof_int [get_sizeof "int" 4]
> -- 
> 1.9.0
>