How to upgrade ROM-based plug-ins securely

Phone manufacturers may want to provide installable upgrades to plug-ins that have been delivered in a phone's ROM, to fix defects or to add functionality. This can be done, but only if certain conditions are met for both the original ROM plug-in and for the upgrade. This page describes these conditions.

Note that ECom finds and uses installed plug-in upgrades even if:

• client code uses the ROM-only plug-in resolver, as described in Using the ROM-only resolver

• the plug-in location is specified at ROM build time using a SPI file.

ROM plug-in conditions

Only plug-ins made upgradable when the ROM is originally built can be upgraded. To do this:

• Provide a SIS stub package for the plug-in DLL on the same drive as the plug-in.

  This step is part of the general mechanism that allows ROM-based files to be upgraded. The SIS file provides information that the Software Installer program uses to identify the replacement file as a valid upgrade of the original file. For more details of how to do this, see Installing language independent files.

• In the plug-in's registration file, set the rom_only setting to 0.

  If rom_only is set to 1, then upgrades are ignored. For details of this flag, see Preventing a ROM-based implementation from being overridden.

Plug-in upgrade conditions

When you create the plug-in upgrade, ensure that the following conditions are met:

• The upgrade supplies both the plug-in DLL and the built resource file, with the same file names as the original ROM plug-in.

• The interface UID and the implementation UID are the same in the upgrade and the original.

  If the values are different, ECom treats the upgrade plug-in as a new implementation.

• The DLL's Vendor ID is the same in the upgrade and the original.

  Software Install will check the Vendor ID of the upgrade DLL matches the original DLL’s Vendor ID.

• The version number (version_no setting) of the implementation, as specified in the registration resource file, is higher in the upgrade than in the original. See How to provide registry information for more information.