Loader -Overview

Key concepts

The loader server

The Symbian platform loader is a server. -The loader server has no public client interface. The client interface is -internal to Symbian platform. Requests to load an EXE or a DLL are passed -to the loader when you do the following:

start a new process -- a call to RProcess::Create()
load a DLL - a call -to RLibrary::Load()
load a logical device -driver - a call to User::LoadLogicalDevice(). A logical -device driver is a type of DLL.
load a physical device -driver - a call to User::LoadPhysicalDevice(). A physical -device driver is a type of DLL.
load a file system - -a call to RFs::AddFileSystem(). A file system is a type -of DLL. A call to RFs::AddFileSystem() requires DiskAdmin +
Purpose
The loader makes EXEs and DLLs ready to run.

The build +tools compile the source code into an executable file. An executable +file is called a binary. The build tools arrange the compiled code +into EXEs and DLLs. The source code, header files and other information +that defines an executable file is defined in an mmp file. The loader +applies relocation information to the code and data sections of EXEs +and DLLs. The loader also loads DLLs that are referred to by other +EXEs and DLLs. EXEs and DLLs can then run in the process into which +they are loaded.

+
Key +concepts
The loader server

The Symbian platform loader is a +server. The loader server has no public client interface. The client +interface is internal to Symbian platform. Requests to load an EXE +or a DLL are passed to the loader when you do the following:
- start a new +process - a call to RProcess::Create()
- load a DLL - +a call to RLibrary::Load()
- load a logical +device driver - a call to User::LoadLogicalDevice(). A logical device driver is a type of DLL.
- load a physical +device driver - a call to User::LoadPhysicalDevice(). A physical device driver is a type of DLL.
- load a file +system - a call to RFs::AddFileSystem(). A file +system is a type of DLL. A call to RFs::AddFileSystem() requires DiskAdmin capability. See ECapabilityDiskAdmin.
- load a file +server extension - call to RFs::AddExtension(). +A file server extension is a type of DLL. This function requires DiskAdmin capability. See ECapabilityDiskAdmin.
- load a file server extension -- call to RFs::AddExtension(). A file server extension -is a type of DLL. This function requires DiskAdmin capability. See ECapabilityDiskAdmin.
- load a locale - a call -to TExtendedLocale::LoadLocale().
Version -numbers

The -reason for version numbers

More than one version of an EXE can -exist on a device at the same time. More than one version of a DLL can exist -on a device at the same time. A device can store versions of an EXE or DLL -that are not compatible with an older version of that EXE or DLL.

A -version number is a set of two numbers. The loader uses these numbers to identify -copies of the executable file. The two numbers are called the major version -number and the minor version number. The build tools encode the two numbers -into the header of the executable file. When a DLL is built, the version numbers -are encoded into the import library.

The -structure of version information

DLLs are the most common users -of versions. You assign new values to the version numbers of a DLL when you -change the published API of the DLL. Symbian recommends the following procedure:
- change the minor version -number if you make a change to a DLL that is backward compatible. An example -is a new function in the DLL.
- change the major version -number if you make a change to a DLL that breaks an interface. An example -is the removal of a function or a change to the signature of a function. An -interface break is disruptive and must be prevented.
The major and minor version numbers are defined in the .mmp file -that defines the source code, header files and other options that apply to -the executable file.

If you do not specify version numbers, the build -tools apply the following default values:
- Major version number -: 10
- Minor version number -: 0
The major version number and the minor version number are stored -in the header of an EXE and DLL. The two numbers are stored in a single 32 -bit value. The high 16 bits hold the major version number. The low 16 bits -hold the minor version number.

When you build a DLL, the build tools -encode the version numbers into the filename of the import library (the .lib file). -The build tools also create an import library that does not have the version -numbers encoded as part of the filename.The following example shows how the -version numbers are encoded in the filename. The major version number is (decimal) -11 and the minor version number is (decimal) 2. The version numbers in the -filename are in hexadecimal.

abcdsrv{000B0002}.lib

Notes:
- The left bracket and -the right bracket are part of the name.
- The first four digits -after the open bracket are the hexadecimal representation of the major version -number.
- The second four digits -are the hexadecimal representation of the minor version number.
The build tools do not encode the version numbers in the filename -of the executable file.

Loader -search rules

EXEs and DLLs can exist on more than one drive. There -can be more than one version of an EXE and more than one version of a DLL. -The loader uses search rules to select the EXE and DLL to load.

See Loader search rules

Emulator

Version numbers are stored in import files for DLLs -that run on devices and the emulator. Version numbers change how the loader -functions on devices, but not in the emulator. You cannot encode the version -numbers in the import library file name on the emulator.

Tools support

Use the build tools to apply version numbers -to EXEs and DLLs. You specify version numbers in the .mmp file -that describes the EXE or DLL.

See also mmp -file syntax and Build -tools guide.
+
load a locale +- a call to TExtendedLocale::LoadLocale().

Version numbers

The reason for version numbers

More than one version +of an EXE can exist on a device at the same time. More than one version +of a DLL can exist on a device at the same time. A device can store +versions of an EXE or DLL that are not compatible with an older version +of that EXE or DLL.

A version number is a set of two numbers. +The loader uses these numbers to identify copies of the executable +file. The two numbers are called the major version number and the +minor version number. The build tools encode the two numbers into +the header of the executable file. When a DLL is built, the version +numbers are encoded into the import library.

The structure of version information

DLLs are the +most common users of versions. You assign new values to the version +numbers of a DLL when you change the published API of the DLL. Symbian +recommends the following procedure:

change the minor +version number if you make a change to a DLL that is backward compatible. +An example is a new function in the DLL.
change the major +version number if you make a change to a DLL that breaks an interface. +An example is the removal of a function or a change to the signature +of a function. An interface break is disruptive and must be prevented.

The major and minor version numbers are defined in the .mmp file that defines the source code, header files and +other options that apply to the executable file.

If you do +not specify version numbers, the build tools apply the following default +values:

Major version +number : 10
Minor version +number : 0

The major version number and the minor version number are +stored in the header of an EXE and DLL. The two numbers are stored +in a single 32 bit value. The high 16 bits hold the major version +number. The low 16 bits hold the minor version number.

When +you build a DLL, the build tools encode the version numbers into the +filename of the import library (the .lib file). +The build tools also create an import library that does not have the +version numbers encoded as part of the filename.The following example +shows how the version numbers are encoded in the filename. The major +version number is (decimal) 11 and the minor version number is (decimal) +2. The version numbers in the filename are in hexadecimal.

abcdsrv{000B0002}.lib

Notes:

The left bracket +and the right bracket are part of the name.
The first four +digits after the open bracket are the hexadecimal representation of +the major version number.
The second four +digits are the hexadecimal representation of the minor version number.

The build tools do not encode the version numbers in the +filename of the executable file.

Loader search rules

EXEs and DLLs can exist on more +than one drive. There can be more than one version of an EXE and more +than one version of a DLL. The loader uses search rules to select +the EXE and DLL to load.

See Loader search rules

Emulator

Version numbers are stored in import files +for DLLs that run on devices and the emulator. Version numbers change +how the loader functions on devices, but not in the emulator. You +cannot encode the version numbers in the import library file name +on the emulator.

Tools support

Use the build tools to apply version +numbers to EXEs and DLLs. You specify version numbers in the .mmp file that describes the EXE or DLL.

See also MMP file syntax in Symbian Tools Guide > Building + > Symbian Build System (SBSv1) > Build tools reference.