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Command pcustom

gef provides a way to create and apply to the currently debugged environment, any new structure (in the C-struct way). On top of simply displaying known and user-defined structures, it also allows to apply those structures to the current context. It intends to mimic the very useful WinDBG dt command.

This is achieved via the command pcustom (for print custom), or you can use its alias, dt (in reference to the WinDBG command) as provided by the WinDbg compatibility extension


New structures can be stored in the location given by the configuration setting:

gef➤ gef config pcustom.struct_path

By default, this location is in $TEMP/gef/structs (e.g. /tmp/user/1000/gef/structs). The structure can be created as a simple ctypes structure, in a file called <struct_name>.py.

You can naturally set this path to a new location

gef➤ gef config pcustom.struct_path /my/new/location

And save this change so you can re-use it directly next time you use gdb

gef➤ gef save
[+] Configuration saved to '~/.gef.rc'

Using user-defined structures

You can list existing custom structures via

gef➤  pcustom list
[+] Listing custom structures from '/tmp/structs'
 →  /tmp/structs/ (A, B)
 →  /tmp/structs/ (elf32_t)
 →  /tmp/structs/ (elf64_t)

To create or edit a structure, use pcustom edit <struct_name> to spawn your EDITOR with the targeted structure. If the file does not exist, gef will nicely create the tree and file, and fill it with a ctypes template that you can use straight away!

gef➤  pcustom new mystruct_t
[+] Creating '/tmp/gef/structs/' from template

If the structure already exists, GEF will open the text editor to edit the known structure. This is equivalent to:

gef➤  pcustom edit elf32_t
[+] Editing '/home/hugsy/code/gef-extras/structs/'

Static ctypes.Structure-like classes

The code can be defined just as any Python (using ctypes) code.

from ctypes import *

typedef struct {
  int age;
  char name[256];
  int id;
} person_t;

class person_t(Structure):
    _fields_ = [
        ("age",  c_int),
        ("name", c_char * 256),
        ("id", c_int),

    _values_ = [
        # You can define a function to substitute the value
        ("age", lambda age: "Old" if age > 40 else "Young"),
        # Or alternatively a list of 2-tuples
        ("id", [
            (0, "root"),
            (1, "normal user"),
            (None, "Invalid person")

pcustom requires at least one argument, which is the name of the structure. With only one argument, pcustom will dump all the fields of this structure.

gef➤  dt person_t
+0000   age          c_int   /* size=0x4 */
+0004   name         c_char_Array_256   /* size=0x100 */
+0104   id           c_int   /* size=0x4 */

By providing an address or a GDB symbol, gef will apply this user-defined structure to the specified address:


This means that we can now create very easily new user-defined structures

For a full demo, watch the following tutorial:


Additionally, if you have successfully configured your IDA settings, you can also directly import the structure(s) that was(were) reverse-engineered in IDA directly in your GDB session: ida-structure-examples - (see gef-extras/ida-rpyc, which is the new improved version of ida-interact)

Dynamic ctypes.Structure-like classes

pcustom also supports the use of class factories to create a ctypes.Structure class whose structure will be adjusted based on the runtime information we provide (information about the currently debugged binary, the architecture, the size of a pointer and more).

The syntax is relatively close to the way we use to create static classes (see above), but instead we define a function that will generate the class. The requirements for this class factory are:

  • Take a single Gef positional argument
  • End the function name with _t

To continue the person_t function we defined in the example above, we could modify the static class as a dynamic one very easily:

import ctypes
from typing import Optional

def person_t(gef: Optional["Gef"]=None):
    fields = [
        ("age",  ctypes.c_int),
        ("name", ctypes.c_char * 256),
        ("id", ctypes.c_int),

    class person_cls(ctypes.Structure):
      _fields_ = fields

    return person_cls

Thanks to the gef parameter, the structure can be transparently adjusted so that GEF will parse it differently with its runtime information. For example, we can add constraints to the example above:

import ctypes
from typing import Optional

def person_t(gef: Optional["Gef"]==None):
    fields = [
        ("age",  ctypes.c_uint8),
        ("name", ctypes.c_char * 256),
        ("id", ctypes.c_uint8),

    # constraint on the libc version
    if gef.libc.version > (2, 27):
      # or on the pointer size
      pointer_type = ctypes.c_uint64 if gef.arch.ptrsize == 8 else ctypes.c_uint32
      fields += [
        ("new_field", pointer_size)

    class person_cls(ctypes.Structure):
      _fields_ = fields

    return person_cls

Public repository of structures

A community contributed repository of structures can be found in gef-extras. To deploy it:

In bash:

git clone


gef➤ gef config pcustom.struct_path /path/to/gef-extras/structs
gef➤ gef save

Then either close GDB or gef reload. You can confirm the structures were correctly loaded in GEF's prompt:

gef➤ pcustom list

Should return several entries.

And remember this is collaborative repository, so feel free to contribute too!