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Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction to GDB Python Pierre-Marie de Rodat [email protected] PM @ {rezosup, freenode, geeknode, . . . } http://lse.epita.fr February 12, 2013

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Page 1: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

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.

Introduction to GDB Python

Pierre-Marie de Rodat

[email protected] @ {rezosup, freenode, geeknode, . . . }

http://lse.epita.fr

February 12, 2013

http://lse.epita.fr
Page 2: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

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Plan

...1 Introduction

Page 3: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

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.....

.....

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......

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.....

......

.....

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......

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.

GDB

Well known source-level debugger from the GNUProjectCan be scripted using a quite resticting specificlanguage (one more to learn!)As far as I could read, it can only define macros

Page 4: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

GDB

Well known source-level debugger from the GNUProjectCan be scripted using a quite resticting specificlanguage (one more to learn!)As far as I could read, it can only define macros

Page 5: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

GDB

Well known source-level debugger from the GNUProjectCan be scripted using a quite resticting specificlanguage (one more to learn!)As far as I could read, it can only define macros

Page 6: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

PythonGDB

GDB 7 introduced Python scripting capabilitiesIt can be accessed through a dedicated API (gdbmodule)This API enables scripts to:

Define pretty-printers for types defined in debuggedprograms (inferiors)Define new commands (like macros)Deal with symbols, stack frames, values typeInspect and modify inferiors memoryRegister callbacks for events (inferior termination,. . . )Set breakpoints. . .

Page 7: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

PythonGDB

GDB 7 introduced Python scripting capabilitiesIt can be accessed through a dedicated API (gdbmodule)This API enables scripts to:

Define pretty-printers for types defined in debuggedprograms (inferiors)Define new commands (like macros)Deal with symbols, stack frames, values typeInspect and modify inferiors memoryRegister callbacks for events (inferior termination,. . . )Set breakpoints. . .

Page 8: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

PythonGDB

GDB 7 introduced Python scripting capabilitiesIt can be accessed through a dedicated API (gdbmodule)This API enables scripts to:

Define pretty-printers for types defined in debuggedprograms (inferiors)Define new commands (like macros)Deal with symbols, stack frames, values typeInspect and modify inferiors memoryRegister callbacks for events (inferior termination,. . . )Set breakpoints. . .

Page 9: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

PythonGDB

GDB 7 introduced Python scripting capabilitiesIt can be accessed through a dedicated API (gdbmodule)This API enables scripts to:

Define pretty-printers for types defined in debuggedprograms (inferiors)Define new commands (like macros)Deal with symbols, stack frames, values typeInspect and modify inferiors memoryRegister callbacks for events (inferior termination,. . . )Set breakpoints. . .

Page 10: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

PythonGDB

GDB 7 introduced Python scripting capabilitiesIt can be accessed through a dedicated API (gdbmodule)This API enables scripts to:

Define pretty-printers for types defined in debuggedprograms (inferiors)Define new commands (like macros)Deal with symbols, stack frames, values typeInspect and modify inferiors memoryRegister callbacks for events (inferior termination,. . . )Set breakpoints. . .

Page 11: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

PythonGDB

GDB 7 introduced Python scripting capabilitiesIt can be accessed through a dedicated API (gdbmodule)This API enables scripts to:

Define pretty-printers for types defined in debuggedprograms (inferiors)Define new commands (like macros)Deal with symbols, stack frames, values typeInspect and modify inferiors memoryRegister callbacks for events (inferior termination,. . . )Set breakpoints. . .

Page 12: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

PythonGDB

GDB 7 introduced Python scripting capabilitiesIt can be accessed through a dedicated API (gdbmodule)This API enables scripts to:

Define pretty-printers for types defined in debuggedprograms (inferiors)Define new commands (like macros)Deal with symbols, stack frames, values typeInspect and modify inferiors memoryRegister callbacks for events (inferior termination,. . . )Set breakpoints. . .

Page 13: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

PythonGDB

GDB 7 introduced Python scripting capabilitiesIt can be accessed through a dedicated API (gdbmodule)This API enables scripts to:

Define pretty-printers for types defined in debuggedprograms (inferiors)Define new commands (like macros)Deal with symbols, stack frames, values typeInspect and modify inferiors memoryRegister callbacks for events (inferior termination,. . . )Set breakpoints. . .

Page 14: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Plan

...2 Usage examplesLoading scriptsDefining a pretty-printerDefining breakpointsConvenience functions

Page 15: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Loading scripts

Most simple way (by hand):source my_script.py

gdb my_program -ex"source my_script.py"

Auto-loading (eg. for libraries):Enable auto-load python-scriptsRename your script to objfile-gdb.pyFix security-related settings (scripts-directory,safe-path, . . . )

Other strange ways (.debug_gdb_scripts) . . .

Page 16: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Loading scripts

Most simple way (by hand):source my_script.py

gdb my_program -ex"source my_script.py"

Auto-loading (eg. for libraries):Enable auto-load python-scriptsRename your script to objfile-gdb.pyFix security-related settings (scripts-directory,safe-path, . . . )

Other strange ways (.debug_gdb_scripts) . . .

Page 17: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Loading scripts

Most simple way (by hand):source my_script.py

gdb my_program -ex"source my_script.py"

Auto-loading (eg. for libraries):Enable auto-load python-scriptsRename your script to objfile-gdb.pyFix security-related settings (scripts-directory,safe-path, . . . )

Other strange ways (.debug_gdb_scripts) . . .

Page 18: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Loading scripts

Most simple way (by hand):source my_script.py

gdb my_program -ex"source my_script.py"

Auto-loading (eg. for libraries):Enable auto-load python-scriptsRename your script to objfile-gdb.pyFix security-related settings (scripts-directory,safe-path, . . . )

Other strange ways (.debug_gdb_scripts) . . .

Page 19: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Loading scripts

Most simple way (by hand):source my_script.py

gdb my_program -ex"source my_script.py"

Auto-loading (eg. for libraries):Enable auto-load python-scriptsRename your script to objfile-gdb.pyFix security-related settings (scripts-directory,safe-path, . . . )

Other strange ways (.debug_gdb_scripts) . . .

Page 20: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Why? (1/2)

GDB itself can pretty-print process data followingthe (eg. C) layout (with -g)

struct my_list{

int value;struct my_list *next;

};...struct my_list *my_list = ...

(gdb) print my_list$1 = (struct my_list *) 0x7fffffffe200(gdb) print *my_list$2 = {value = 0, next = 0x7fffffffe210}(gdb) print *my_list->next$3 = {value = 1, next = 0x7fffffffe220}

Page 21: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Why? (1/2)

GDB itself can pretty-print process data followingthe (eg. C) layout (with -g)

struct my_list{

int value;struct my_list *next;

};...struct my_list *my_list = ...

(gdb) print my_list$1 = (struct my_list *) 0x7fffffffe200(gdb) print *my_list$2 = {value = 0, next = 0x7fffffffe210}(gdb) print *my_list->next$3 = {value = 1, next = 0x7fffffffe220}

Page 22: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Why? (1/2)

GDB itself can pretty-print process data followingthe (eg. C) layout (with -g)

struct my_list{

int value;struct my_list *next;

};...struct my_list *my_list = ...

(gdb) print my_list$1 = (struct my_list *) 0x7fffffffe200(gdb) print *my_list$2 = {value = 0, next = 0x7fffffffe210}(gdb) print *my_list->next$3 = {value = 1, next = 0x7fffffffe220}

Page 23: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Why? (2/2)

Useful to debug low-level stuff, not algorithmsRegister pretty-printers for your data types and printthem!Container libraries (like the libstdc++) alreadybundle some

Page 24: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Why? (2/2)

Useful to debug low-level stuff, not algorithmsRegister pretty-printers for your data types and printthem!Container libraries (like the libstdc++) alreadybundle some

Page 25: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Why? (2/2)

Useful to debug low-level stuff, not algorithmsRegister pretty-printers for your data types and printthem!Container libraries (like the libstdc++) alreadybundle some

Page 26: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Example — Definition

import gdb

class MyListPrinter(object):’’’Print a struct my_list (*)’’’

def __init__(self, value):my_list_type = \

gdb.lookup_type(’struct my_list’)self.value = (value.address

if value.type == my_list_typeelse value)

def to_string(self):elts, node_p = [], self.valuewhile node_p != gdb.Value(0):

node = node_p.dereference()elts.append(str(node[’value’]))node_p = node[’next’]

return ’[{}]’.format(’; ’.join(elts))

Page 27: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Example — Registering

Pretty-printer matching can be very complexThink about generic data structure in C++. . .GDB has a list of (user provided) "value handlers" tolook for a pretty-printer"handlers" are called with the value to printIf one of them returns a pretty-printer, GDB uses it.

def my_list_lookup(value):my_list_type = gdb.lookup_type(’struct my_list’)my_list_p = gdb.Type.pointer(my_list_type)if value.type in (my_list_type, my_list_p):

return MyListPrinter(value)else:

return None

gdb.pretty_printers.append(my_list_lookup)

Page 28: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Example — Registering

Pretty-printer matching can be very complexThink about generic data structure in C++. . .GDB has a list of (user provided) "value handlers" tolook for a pretty-printer"handlers" are called with the value to printIf one of them returns a pretty-printer, GDB uses it.

def my_list_lookup(value):my_list_type = gdb.lookup_type(’struct my_list’)my_list_p = gdb.Type.pointer(my_list_type)if value.type in (my_list_type, my_list_p):

return MyListPrinter(value)else:

return None

gdb.pretty_printers.append(my_list_lookup)

Page 29: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Example — Registering

Pretty-printer matching can be very complexThink about generic data structure in C++. . .GDB has a list of (user provided) "value handlers" tolook for a pretty-printer"handlers" are called with the value to printIf one of them returns a pretty-printer, GDB uses it.

def my_list_lookup(value):my_list_type = gdb.lookup_type(’struct my_list’)my_list_p = gdb.Type.pointer(my_list_type)if value.type in (my_list_type, my_list_p):

return MyListPrinter(value)else:

return None

gdb.pretty_printers.append(my_list_lookup)

Page 30: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Example — Registering

Pretty-printer matching can be very complexThink about generic data structure in C++. . .GDB has a list of (user provided) "value handlers" tolook for a pretty-printer"handlers" are called with the value to printIf one of them returns a pretty-printer, GDB uses it.

def my_list_lookup(value):my_list_type = gdb.lookup_type(’struct my_list’)my_list_p = gdb.Type.pointer(my_list_type)if value.type in (my_list_type, my_list_p):

return MyListPrinter(value)else:

return None

gdb.pretty_printers.append(my_list_lookup)

Page 31: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Example — Registering

Pretty-printer matching can be very complexThink about generic data structure in C++. . .GDB has a list of (user provided) "value handlers" tolook for a pretty-printer"handlers" are called with the value to printIf one of them returns a pretty-printer, GDB uses it.

def my_list_lookup(value):my_list_type = gdb.lookup_type(’struct my_list’)my_list_p = gdb.Type.pointer(my_list_type)if value.type in (my_list_type, my_list_p):

return MyListPrinter(value)else:

return None

gdb.pretty_printers.append(my_list_lookup)

Page 32: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

..........

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

.....

.....

......

.....

......

.....

.....

.

Example — Usage

(gdb) source my_script.py(gdb) print my_list$1 = [0; 1; 2; 3](gdb) print *my_list$2 = [0; 1; 2; 3](gdb) print /r *my_list$3 = {value = 0, next = 0x7fffffffe210}

(gdb) print my_struct$4 = {

str = 0x4005f4 "Hello, world!\n",code = 204,args = [0; 1; 2; 3]

}

Page 33: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

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Example — Usage

(gdb) source my_script.py(gdb) print my_list$1 = [0; 1; 2; 3](gdb) print *my_list$2 = [0; 1; 2; 3](gdb) print /r *my_list$3 = {value = 0, next = 0x7fffffffe210}

(gdb) print my_struct$4 = {

str = 0x4005f4 "Hello, world!\n",code = 204,args = [0; 1; 2; 3]

}

Page 34: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

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Use case

You want to compute statistics abount function calls.Say you have a factorial function:#include <stdio.h>

unsigned fact(unsigned n){

if (n <= 1) return 1;else return n * fact(n - 1);

}

void print_fact(unsigned n){ printf("fact(%u) =\t%u\n", n, fact(n)); }

int main(void){

unsigned i, n = 0;for (i = 0; i<100; ++i, n=(n+7)%17)

print_fact(n);}

You want to know how many times fact is called foreach argument value.

Page 35: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

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Example — Breakpoint definition

from collections import defaultdictimport gdb

class FactHistogram(gdb.Breakpoint):def __init__(self):

super(FactHistogram, self).__init__(’fact’, internal=True)

# By default, a value is never used.self.histogram = defaultdict(lambda: 0)

def stop(self):arg = int(gdb.newest_frame().read_var(’n’))self.histogram[arg] += 1return False # Resume execution

fact_histo = FactHistogram()

Page 36: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

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Example — Helper command definition

class PrintHistogram(gdb.Command):def __init__(self):

super(PrintHistogram, self).__init__(’histo’, gdb.COMMAND_BREAKPOINTS,gdb.COMPLETE_NONE)

def invoke(self, argument, from_tty):for arg, times in sorted(

fact_histo.histogram.items(),key=lambda item: item[1]):gdb.write(’fact({}):\t{} times\n’.format(

arg, times))

PrintHistogram()

Page 37: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

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Example — Usage

(gdb) source my_script.py(gdb) rStarting program: /tmp/fact.cfact(0) = 1fact(7) = 5040fact(14) = 1278945280[...]fact(16) = 2004189184fact(6) = 720fact(13) = 1932053504[Inferior 1 (process 7605) exited with code 03](gdb) histofact(0): 6 timesfact(16): 6 timesfact(15): 12 times[...]fact(5): 71 timesfact(4): 77 timesfact(3): 82 timesfact(2): 88 timesfact(1): 94 times

Page 38: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

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Example — Debugged program

#include <stdio.h>

typedef void (*callback_fn)(int);

static void internal_callback(int no){ printf("Internal callback call with no = %d\n", no); }

callback_fn get_callback(void){ return internal_callback; }

void internal_process_something(void){ get_callback()(0xcd); }

int main(void){

internal_process_something();get_callback()(0xcc);return 0;

}

Page 39: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

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Example — Convenience function definition

import gdb

class ForbiddenCaller(gdb.Function):def __init__(self):

super(ForbiddenCaller, self).__init__(’forbidden_caller’)def invoke(self, prefix):

prefix = prefix.string()frame = gdb.newest_frame().older()fr_name = frame.name()return not fr_name.startswith(prefix)

ForbiddenCaller()

Page 40: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examplesLoading scripts

Defining a pretty-printer

Defining breakpoints

Convenience functions

Conclusion

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Example — Usage

(gdb) source my_script.py(gdb) b internal_callback if $forbidden_call("internal_")Breakpoint 1 at 0x400507: file callback.c, line 7.(gdb) rStarting program: /tmp/callbackInternal callback call with no = 205

Breakpoint 1, internal_callback (no=204) at callback.c:77 printf("Internal callback call with no = %d\n", no);(gdb) bt#0 internal_callback (no=204) at callback.c:7#1 0x000000000040054f in main () at callback.c:23

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Plan

...3 Conclusion

Page 42: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

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Usage examples

Conclusion

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Conclusion

The Python API is really easy to useIt looks more powerful than the specific languageIt is still evolving: stay tuned!

Page 43: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

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Conclusion

The Python API is really easy to useIt looks more powerful than the specific languageIt is still evolving: stay tuned!

Page 44: Introduction to GDB Python - lse.epita.fr · Introduction to GDB Python Pierre-Marie de Rodat Introduction Usage examples Conclusion..... GDB Well known source-level debugger from

Introduction toGDB Python

Pierre-Marie deRodat

Introduction

Usage examples

Conclusion

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Conclusion

The Python API is really easy to useIt looks more powerful than the specific languageIt is still evolving: stay tuned!


Introduzione a GDB · Introduzione a GDB UnderAttHack by Hackingeasy Team Introduzione a GDB 0x00000001 Introduzione: GDB è un acronimo che sta per “GNU Project Debugger” ovvero

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