2.3 The type section

This section is the most important section in CTF, describing all the top-level types in the program. It consists of an array of type structures, each of which describes a type of some kind: each kind of type has some amount of variable-length data associated with it (some kinds have none). The amount of variable-length data associated with a given type can be determined by inspecting the type, so the reading code can walk through the types in sequence at opening time.

Each type structure is one of a set of overlapping structures in a discriminated union of sorts: the variable-length data for each type immediately follows the type’s type structure. Here’s the largest of the overlapping structures, which is only needed for huge types and so is very rarely seen:

typedef struct ctf_type
{
  uint32_t ctt_name;
  uint32_t ctt_info;
  __extension__
  union
  {
    uint32_t ctt_size;
    uint32_t ctt_type;
  };
  uint32_t ctt_lsizehi;
  uint32_t ctt_lsizelo;
} ctf_type_t;

Here’s the much more common smaller form:

typedef struct ctf_stype
{
  uint32_t ctt_name;
  uint32_t ctt_info;
  __extension__
  union
  {
    uint32_t ctt_size;
    uint32_t ctt_type;
  };
} ctf_type_t;

If ctt_size is the #define CTF_LSIZE_SENT, 0xffffffff, this type is described by a ctf_type_t: otherwise, a ctf_stype_t.

Here’s what the fields mean:

Two aspects of this need further explanation: the info word, and what exactly a type ID is and how you determine it. (Information on the various type-kind- dependent things, like whether ctt_size or ctt_type is used, is described in the section devoted to each kind.)