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

Tom Tromey
2014-05-08T18:47:20Z

It is valid in C to have a VLA in a struct or union type, but gdb did
not handle this.

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