=============================================
Python for S60 on S60 3rd Edition, 28.06.2006
=============================================
Contents:
1. Introduction
2. Overview of PyS60 on S60 3rd Edition
3. Standard development lifecycle in 3rd Edition
3.1 Signing and distribution
3.2 Module level details
4. File locations
5. Capabilities
6. Native extensions
6.1 ABI compatibility
6.2 Porting existing native extensions to PyS60
7. Summary
8. Glossary
1. Introduction
---------------
This document describes the changes to Python for S60 (hereafter PyS60) needed
in order to support S60 3rd Edition (hereafter also S60 3rdEd). These changes
and advices described are not applicable to PyS60 running on S60 1st or 2nd
Edition and the developers on these platforms are not affected in any way.
The new platform security (hereafter platsec) features in Symbian OS 9.x/EKA2,
and S60 3rdEd onwards require several changes to the whole PyS60 framework.
Without these modifications S60 3rd Edition would not be supported by PyS60. The
implementation alternative selected in order to support PyS60 3rd Edition is
tightly aligned with the common EKA2 platform security framework in order to
minimize the work for a PyS60 developer. At the same time this limits the possible
security threats posed by PyS60.
The solution for PyS60 in EKA2 is based on two use cases:
1. Stand-alone installation - in essence this makes Python applications no
different from native Symbian applications, a user cannot tell whether this is
a Python or C++ application. The application is visible in the device main
menu
2. Plain script running and the application to enable this, aka script shell
the Python application seen in PyS60 1.0 onwards
In this document we provide information how the new platform security features
affect PyS60, what will be the development options and offer advices for native
extending.
For all questions and feedback, related to PyS60 and platsec, please use the
Forum Nokia discussion board:
http://discussion.forum.nokia.com/forum/forumdisplay.php?f=102
Tip: use the advanced search option with keyword "platsec" and select the Python
forum for the search.
2. Overview of PyS60 on S60 3rdEd
---------------------------------
In 3rdEd devices, platsec is enforced. This means that all the installed SISX
files need to be signed (NB. there might be an option to install unsigned
packages in some devices). Unsigned packages cannot be installed to a device and
neither the old style SIS packages nor the binaries packaged from 2ndEd or 1stEd
are compatible with the 3rdEd.
The software installer (hereafter SWInstall) will check if the application in
the SISX package is signed. For more information about signing, see the Section
"Signing".
A fundamental concept in platsec is 'capability' which is the term used for what
the running process can do in the device - process is the basic insulation
granularity in platsec and capabilities are forced during runtime. A capability
must be held by the executable binary if the process needs to access some
restricted resource.
Since a standalone PyS60 application is no different from a native application
and runs in a separate process it needs to be signed if it uses controlled APIs or
it is distributed via a SISX package.
What a Python standalone application can do will be limited by the capabilities
assigned to the interpreter DLL - these capabilities are listed in Section 5.
"Capabilities". In other words, this is the upper bound for any Python
application which uses the Nokia signed PyS60 distribution. There is of course
the possibility to sign the Python interpreter DLL for special purposes with
larger capabilities if needed but this discussion is left out from this
document.
As the Python application seen from the device main menu, aka script shell, is
also a Python application it needs to be signed. The script shell should not
enable the running of scripts with large capabilities and thus it is not signed
by Nokia with the same capabilities as the interpreter DLL. This should not
cause problems for development - a developer can sign the script shell
application with developer certificate (hereafter devcert). Due to separate
signing needs for the interpreter DLL and the script shell application, there is
need for two separate packages ('X' indicates version number):
* PythonForS60-X_X_X_3rded.SIS - contains the interpreter DLL, all the Nokia
provided native Python extensions and other needed files
* PythonScriptShell-X_X_X_3rded.SIS - contains the script shell application,
does not work without the above package
A developer should keep in mind that the script shell is just a normal
application, similar to the one you wrap with py2sis and subject to the same
security preconditions as described earlier in this document. The interpreter
DLL is the one used by all the standalone Python applications and the entity
that needs to be signed with a large set of capabilities to ensure that
individual Python applications can access the controlled resources as freely as
possible. Notice that the script shell Python application visible in the device
main menu has nothing to do with other standalone Python applications (ie. there
are no logical or conceptual dependencies).
Here is an outline of a standalone Python application in 3rdEd devices:
default.py
| (wrapped together with 'foobar.exe' e.g. with py2sis)
|
foobar_0x01234567.exe
| (a simple launchpad application for interpreter creation etc.
| Another example is 'Python.exe', the script shell executable)
python222.dll
| (shared between standalone Python applications)
|
location.pyd
(all the other native extensions are at this level also)
In the above diagram, the 'python222.dll' is signed by Nokia, and as stated
previously, it provides the upper bound for what the 'foobar.exe' can access (in
the platsec sense) in the device. For the 'foobar.exe' the developer has chosen
a suitable set of capabilities limited by the developer's certificate and/or the
Python APIs utilized. The capabilities needed for the APIs are outlined in
Section 3.2.
For more information, please see the platsec material provided by Symbian and
Nokia, e.g. here is an overview of the Symbian signed process and platsec:
https://www.symbiansigned.com/How_has_Symbian_Signed_evolved_with_Symbian_OS_v9.pdf
Symbian signed
--------------
In principle, there is no problem in getting a standalone Python application to
be Symbian signed - a standalone Python application is no different from a
native C++ application. Currently there might be problems with some of the
Symbian signed test cases, e.g. PyS60 does not report the possible low memory
situation when it is started and if it is unable to run due to low memory. This
is in conflict with Symbian signed test MEM-01 (see
https://www.symbiansigned.com/app/page/requirements).
3. Standard development lifecycle
---------------------------------
The S60 emulator allows unrestricted access to the platform and therefore the
PyS60 developer is advised to first use the emulator for overall testing of a
Python script. Useful information especially about the platform warnings can be
found from the emulator log file, located usually under:
c:\Documents and Settings\<USERID>\Local Settings\temp\EPOCWIND.OUT
For example, the following warning message would be emitted to the log file if a
script tries to delete a file ("traceback.pyc") under \resource:
64.990 *PlatSec* WARNING - Capability check would have failed - A Message
(function number=0x00000013) from Thread Python[10201510]0001::PYTHON, sent to
Server !FileServer, was checked by Thread EFile.exe[100039e3]0001::Main and
was found to be missing the capabilities: TCB . Additional diagnostic
message: \resource\traceback.pyc Used to call: Delete
The emulator can be configured also to simulate the platsec constraints, see
the SDK documentation for more information (search the SDK with "Platform
Security Tab").
In a device the following would be received if the Python script tries to write
to a restricted/not restricted location (example via Bluetooth console in Nokia
N73):
[GCC 3.4.3 (release) (CodeSourcery ARM Q1C 2005)] on symbian_s60
Type "copyright", "credits" or "license" for more information.
Type "commands" to see the commands available in this simple line editor.
>>> f=open('c:\\sys\\bin\\test.log', 'w')
Traceback (most recent call last):
File "<console>", line 1, in ?
IOError: [Errno -46] : 'c:\\sys\\bin\\test.log'
>>> f=open('c:\\Python\\test.log', 'w')
>>> f.write('foobar')
>>> f.close()
>>>
The first file open fails since location c:\sys\bin is restricted in 3rdEd
devices. The second file open succeeds as this location is not controlled by
platsec - this location is also the folder for scripts seen in the script shell
application. Notice also that the platform security constraints can be handled
at Python level with e.g. try-except constructs.
3.1 Signing and distribution
----------------------------
For executing the scripts in an actual S60 3rdEd device there exists numerous
alternatives for signing and distribution e.g.:
1) Using a devcert for SISX signing
2) Self-signing the SISX
3) Signing the Python script shell application with the above 1) or 2)
alternatives and installing the individual scripts with separate packages
(which need to be signed as well)
4) Packaging the scripts with py2sis (and signing the SISX packages).
By following the first alternative, a developer can sign applications with
devcerts prior the official Symbian signing and test the application in
production devices with almost full capabilities. Again, applications you are
planning to distribute for 3rdEd handsets need to be signed since the platform
security restrictions are taken into use in the target handsets. For obtaining
devcerts, see:
https://www.symbiansigned.com/app/page/devcertgeneral
For the second alternative, self-signing, please see the 3rdEd SDK documentation
for more information:
Introduction to S60 3rd Edition >> How to Sign .sis Files
(or search with keyword "self-sign")
In the third alternative, the Python script shell SIS package is signed with a
devcert or self-signed and the individual script can be packaged to a SISX file
and e.g. Bluetooth beamed to the device. Here is an example ".pkg" file used for
generating a SISX file (for processing this file, please see the above document
about signing):
;
;Languages
&EN
;
; The packages UID from test range
;
#{"MyTestPackage"},(0xE000000F),1,0,0,TYPE=SISAPP
%{"Vendor-EN"}
(0x101F7961), 0, 0, 0, {"Series60ProductID"}
;
; Files to install, this file needs to be found by 'makesis.exe'.
; The file location on the right side is the directory seen by the script shell
; application in the device, you can install your scripts there for easy
; invocation
;
"c:\src\mytest.py" -"c:\Python\mytest.py"
The above example uses UID from range 0xE0000000 - 0xEFFFFFFF, this is reserved
for testing. For more information about UIDs, please see:
https://www.symbiansigned.com/app/page/uidfaq
In the fourth alternative, a developer can use the py2sis program to package
individual scripts to installable SISX packages. The packages generated by
py2sis require the 'PythonForS60-X_X_X_3rded.SIS' to be installed in the device.
For details about py2sis usage, please see 'Py2SIS_3rdED_v0_1_README.txt'.
3.2 Module level details
------------------------
The Python functions or modules affected by platform security are outlined in
the following table:
.--------------------------------------------------------------------------.
| Function or module | Capabilities needed | Devcert | Self-signing |
|--------------------------+----------------------+---------+--------------|
| location.gsm_location()* | ReadUserData, | | |
| | ReadDeviceData, | ACS | |
| | Location | | |
|--------------------------+----------------------+---------+--------------|
| contacts | ReadUserData, | | |
| | WriteUserData, | ACS | |
| | ReadDeviceData, | | |
| | WriteDeviceData | | |
|--------------------------+----------------------+---------+--------------|
| sysinfo.imei() | ReadDeviceData+ | | X |
|--------------------------+----------------------+---------+--------------|
| telephone | NetworkServices | | X |
|--------------------------+----------------------+---------+--------------|
| messaging | NetworkServices | | X |
.--------------------------------------------------------------------------.
ACS = Indicates that a ACS Publisher ID is needed in order to obtain a devcert
of this level.
* = Gives false data if the executable is not signed with the specific
capabilities.
+ = Claimed by the S60 SDK but in practise self-signing is sufficient.
No capabilities needed:
* camera
* e32db
* inbox
* audio
* socket
* graphics
4. File locations
-----------------
In EKA2 the file locations have changed, the concept 'data caging' refers to the
changed and controlled locations. For PyS60 on 3rdEd devices this is seen as
follows:
c:\sys\bin
Contains all the native extensions including all the binary launchpads for
Python applications.
c:\resource
Contains the Python standard library files bundled with the Nokia PyS60 SISX
package.
c:\private\<UID>
Contains the "default.py" script which is the script interpreted first by the
launchpad binaries. The <UID> is the unique identifier assigned to a Python
application. In the Nokia script shell application this is 10201510.
These locations have special constraints, see Symbian and Nokia platsec
documentation for more information. In summary, \sys\bin is the only place where
executable binaries (including DLLs) can exist, \resource can only be read, not
written to (except by TCB programs) and \private\<UID>\ is only accessible by
the process in question (and TCB programs).
Most notably this is seen in the "import" path of the interpreter. The following
is the output from the script shell application using Bluetooth console:
>>> import sys
>>> sys.path
['c:\\private\\10201510', 'c:\\resource']
Notice that the process private directory (in the above example
c:\private\10201510) is a new search location for the interpreter. In this
example it is the one assigned for the Python script shell application. If you
package your application with py2sis, the "import" path will automatically
contain the correct search path similar to the path above but with the UID
assigned to your application. This new search path has implications for native
extensions, see Section 6.2 for more information.
There is a new function for obtaining the process UID in PyS60:
appuifw.app.uid()
Returns the UID, in Unicode, of the native application in whose context the
current Python interpreter session runs.
5. Capabilities
---------------
The capabilities assigned by Nokia to PyS60 excluding the script shell
application are as follows:
User Capabilities:
* NetworkServices
* LocalServices
* ReadUserData
* WriteUserData
* Location
* UserEnvironment
System Capabilities:
* PowerMgmt
* ReadDeviceData
* WriteDeviceData
* TrustedUI
* ProtServ
* SwEvent
* SurroundingsDD
A Python application using the Nokia signed Python SISX package cannot have more
capabilities than in the above list, less is of course possible. If more
capabilities are needed, the Python DLL capabilities need to be changed like
stated before and the SISX package signed with a certificate with enough signing
metacapabilities. For more information, please see the 'README.txt' in the
source distribution.
The script shell application is signed with the following capabilities available
for self-signing:
* LocalServices
* NetworkServices
* ReadUserData
* UserEnvironment
* WriteUserData
6. Native extensions
--------------------
This section highlights some of the changes needed for natively extending PyS60
on EKA2.
6.1 ABI compatibility
---------------------
Nokia binary distribution of PyS60 and the SDK package is compiled with GCCE
which uses ABIv2. The PyS60 SDK package includes the correct .dso files needed
by the linker. Developers have to use either ARMV5_ABIv2 (RVCT 2.2) or GCCE
target for compiling their native extensions for devices.
6.2 Porting existing native extensions to PyS60
-----------------------------------------------
The normal instructions for porting source code from earlier SDKs to 3rdEd
apply. See the 3rdEd SDK documentation for information of the source code
changes.
Here are some changes most likely needed for porting existing native PyS60
extensions:
1) Wrappers needed for all the native extensions.
You need to wrap your native extension with Python script layer (in the below
case 'my_native.py' would be a suitable name) which contains this code:
if e32.s60_version_info>=(3,0):
import imp
_my_native=imp.load_dynamic('_my_native', 'c:\\sys\\bin\\_my_native.pyd')
else:
import _my_native
This makes it possible to locate your pyd-file due to changes in interpreter
search path. The PyS60 convention is to name the compiled pyd to start with
'_' character. Your compiled binary can only locate under \sys\bin and the
wrapper should be located under c:\resource in a device. You need to adapt the
above code to reflect the names of your files and the correct locations.
2) Remove the DLL entrypoint.
Here is an example code snippet:
#ifndef EKA2
GLDEF_C TInt E32Dll(TDllReason)
{
return KErrNone;
}
#endif /*EKA2*/
3) Verify that the init-function is exported in the pyd in ordinal 1.
Try to freeze the exported functions and see that the file
'\EABI\_my_native.frz' contains the correct init function in ordinal 1. If this
is not the case, you might need to use NONSHARABLE_CLASS -macros for the
compiler not to expose internal classes not needed in the interface.
4) Package your extension to a SISX file.
The binary pyds must be installed via SISX files.
Notice that the \sys\bin has a flat file structure. Therefore it is advisable to
add a UID suffix to your native extension in order to prevent name clashes. The
convention is to add "_0x01234567" to the name of the extension (using the
unique UID allocated for this specific DLL).
7. Summary
----------
This document highlighted the changes to PyS60 in 3rdEd. Without these changes
Python would not be supported in 3rdEd devices. The changes outlined in this
document are briefly as follows:
* The script shell application is separated to a new SISX file from the main
Python interpreter distribution. The two SISX files can be signed with different
set of capabilities.
* In order to access broader set of functions in PyS60 and more locations in
the device a developer might need a devcert.
* The location of different Python specific files has changed. This change has
implications e.g. for the interpreter search path.
8. Glossary
-----------
platsec
Platform Security
EKA2
EPOC32 Kernel Architecture 2
capability
A capability, when hold by a running process, gives permission to access
system resources.
RVCT
RealView Compiler Tools (ARM ltd.)
pyd
Binary Python extension (written in C/C++)
PyS60
Python for S60. In this document, this term might refer also to the
interpreter DLL and the native extensions (i.e. pyds)
SISX
The new format used for SIS files by SWInstall (Software Installer). Notice
that the file ending is still .sis
Script shell
In this document, an S60 application visible in the device menu which enables
a user to run individual Python scripts. Part of the Python for S60
distribution
SWInstall
A program running in the target device handling SISX installer packages
TCB
From the 3rdEd SDK: "TCB stands for "Trusted Computing Base." The trusted
computing base consists of a number of architectural elements that cannot be
subverted and that guarantee the integrity of the device. This trusted core
runs with "Tcb" system capability. The components with Tcb capability have
full access to file systems including reading/writing to \sys\bin. TCB is not
granted to third-party applications."
py2sis
The tool to package Python scripts to SIS packages which can be installed by
SWInstall to a Symbian OS device. Part of the Python for S60 distribution
appmgr
Writes Python scripts from device inbox to the location where these can be
interpreted by the script shell. Part of Python for S60 distribution
devcert
Developer certificate. More APIs can be accessed when signing SISX packages
with this certificate, for more information about this please search your SDK
with the terms 'developer certificate' and see
https://www.symbiansigned.com/app/page/devcertgeneral
Copyright (c) 2006 Nokia Corporation. Nokia and Nokia Connecting
People are registered trademarks of Nokia Corporation.
