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<concept id="GUID-A188606F-4A8E-5A85-A241-E15219960EFA" xml:lang="en"><title>Loader

Overview</title><shortdesc>This topic describes the overview, purpose, key concepts and architecture

of loader.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<ul>

<li id="GUID-AE825AB3-3799-5A7A-A74D-D6E457A6997E"><p> <xref href="GUID-A188606F-4A8E-5A85-A241-E15219960EFA.dita#GUID-A188606F-4A8E-5A85-A241-E15219960EFA/GUID-E36370EC-CD5E-54AE-AD62-2BA3B70F5379">Purpose</xref>  </p> </li>

<li id="GUID-9D2C951C-6092-53BB-BFA9-4D33230721FA"><p> <xref href="GUID-A188606F-4A8E-5A85-A241-E15219960EFA.dita#GUID-A188606F-4A8E-5A85-A241-E15219960EFA/GUID-89A8CABD-6B31-5D10-87F6-922CCFB83186">Key concepts</xref>  </p> </li>

<li id="GUID-B21577D8-3B8B-596F-A3B6-6AC2538F6F28"><p> <xref href="GUID-A188606F-4A8E-5A85-A241-E15219960EFA.dita#GUID-A188606F-4A8E-5A85-A241-E15219960EFA/GUID-64154337-D706-5DE1-9319-4FEA6181EFC4">Architectural relationships</xref>  </p> </li>

</ul>

<section id="GUID-E36370EC-CD5E-54AE-AD62-2BA3B70F5379"><title>Purpose</title> <p>The

loader makes EXEs and DLLs ready to run. </p> <p>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. </p> </section>

<section id="GUID-89A8CABD-6B31-5D10-87F6-922CCFB83186"><title>Key concepts</title> <p><b>The loader server</b> </p> <p>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: </p> <ul>

<li id="GUID-5DFBB7F5-2F30-50C7-9144-3D6D85C0ACA1"><p>start a new process

- a call to <xref href="GUID-9DD1EA2B-DC59-315C-8E9C-CE6D9461B695.dita#GUID-9DD1EA2B-DC59-315C-8E9C-CE6D9461B695/GUID-DD214BA3-907E-3C7F-93C6-924A9A115A02"><apiname>RProcess::Create()</apiname></xref>  </p> </li>

<li id="GUID-B88FC041-7643-5CA0-9796-A51E64CAA1DF"><p>load a DLL - a call

to <xref href="GUID-25327159-83D6-3507-B187-09EA4BB3727F.dita#GUID-25327159-83D6-3507-B187-09EA4BB3727F/GUID-4F1B2717-D34F-32A4-B6E6-03D0533186A3"><apiname>RLibrary::Load()</apiname></xref>  </p> </li>

<li id="GUID-A7578989-6BDB-5CEA-B3C3-0B5A08E57166"><p>load a logical device

driver - a call to <xref href="GUID-C197C9A7-EA05-3F24-9854-542E984C612D.dita#GUID-C197C9A7-EA05-3F24-9854-542E984C612D/GUID-AE0D51B7-7ADC-3C9F-ACAA-8F6D9EA0AEFA"><apiname>User::LoadLogicalDevice()</apiname></xref>. A logical

device driver is a type of DLL. </p> </li>

<li id="GUID-34DC54FE-FCEF-5F83-B205-9BA5B7140680"><p>load a physical device

driver - a call to <xref href="GUID-C197C9A7-EA05-3F24-9854-542E984C612D.dita#GUID-C197C9A7-EA05-3F24-9854-542E984C612D/GUID-A0F4BF4A-9C58-3E5E-88E1-6D98597DDA18"><apiname>User::LoadPhysicalDevice()</apiname></xref>. A physical

device driver is a type of DLL. </p> </li>

<li id="GUID-51318E5E-4534-589B-B4BD-92D73F832A6F"><p>load a file system -

a call to <xref href="GUID-E263C747-946F-35AA-9F1D-41833BD350FC.dita#GUID-E263C747-946F-35AA-9F1D-41833BD350FC/GUID-51353BE2-9133-39F5-83F3-A5DB88D858CA"><apiname>RFs::AddFileSystem()</apiname></xref>. A file system is a type

of DLL. A call to <codeph>RFs::AddFileSystem()</codeph> requires DiskAdmin

capability. See <xref href="GUID-99D8A4E8-BC4F-39FF-A3DF-832CF0411629.dita"><apiname>ECapabilityDiskAdmin</apiname></xref>. </p> </li>

<li id="GUID-8394C231-341B-5EA6-B9C2-01F75685813D"><p>load a file server extension

- call to <xref href="GUID-E263C747-946F-35AA-9F1D-41833BD350FC.dita#GUID-E263C747-946F-35AA-9F1D-41833BD350FC/GUID-D45FD363-EEF9-3F77-8FA1-49270D8E89A0"><apiname>RFs::AddExtension()</apiname></xref>. A file server extension

is a type of DLL. This function requires DiskAdmin capability. See <xref href="GUID-99D8A4E8-BC4F-39FF-A3DF-832CF0411629.dita"><apiname>ECapabilityDiskAdmin</apiname></xref>. </p> </li>

<li id="GUID-F1889916-80EB-55B6-BEAF-F66164F3838C"><p>load a locale - a call

to <xref href="GUID-454ACAB5-1573-323C-820E-AF542B149D2A.dita#GUID-454ACAB5-1573-323C-820E-AF542B149D2A/GUID-9F04584E-DD0B-39CE-8666-88F67F3B83BF"><apiname>TExtendedLocale::LoadLocale()</apiname></xref>. </p> </li>

</ul> <p><b>Version

numbers</b> </p> <p><b>The

reason for version numbers</b> </p> <p>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. </p> <p>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. </p> <p><b>The

structure of version information</b> </p> <p>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: </p> <ul>

<li id="GUID-A3D6B7C6-E48E-5374-8EFE-29EB129FEE04"><p>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. </p> </li>

<li id="GUID-F6813400-1E6A-58B9-8360-7FD364F2153A"><p>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. </p> </li>

</ul> <p>The major and minor version numbers are defined in the <filepath>.mmp</filepath> file

that defines the source code, header files and other options that apply to

the executable file. </p> <p>If you do not specify version numbers, the build

tools apply the following default values: </p> <ul>

<li id="GUID-CBF4D098-3A83-53E6-9E54-0A9B487D6E22"><p>Major version number

: 10 </p> </li>

<li id="GUID-46E7516E-988B-5F92-9877-FEE17D3F26A7"><p>Minor version number

: 0 </p> </li>

</ul> <p>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. </p> <p>When you build a DLL, the build tools

encode the version numbers into the filename of the import library (the <filepath>.lib</filepath> 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. </p> <p> <filepath>abcdsrv{000B0002}.lib</filepath>  </p> <p>Notes: </p> <ul>

<li id="GUID-7DC90016-5A54-5939-84B1-DDB0B2D4D9F5"><p>The left bracket and

the right bracket are part of the name. </p> </li>

<li id="GUID-BC291976-EB6D-59D2-8941-64F6ED3AC191"><p>The first four digits

after the open bracket are the hexadecimal representation of the major version

number. </p> </li>

<li id="GUID-51590778-985F-5DCC-9191-E937B1058F51"><p>The second four digits

are the hexadecimal representation of the minor version number. </p> </li>

</ul> <p>The build tools do not encode the version numbers in the filename

of the executable file. </p> <p><b>Loader

search rules</b> </p> <p>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. </p> <p>See <xref href="GUID-D8837969-74D0-5E17-AD42-3F10DD1FD5BF.dita">Loader search rules</xref>  </p> <p><b>Emulator</b> </p> <p>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. </p> <p><b>Tools support</b> </p> <p>Use the build tools to apply version numbers

to EXEs and DLLs. You specify version numbers in the <filepath>.mmp</filepath> file

that describes the EXE or DLL. </p> <p>See also <xref href="GUID-BBBB5000-90A2-503A-9521-2FC6DEC69DC8.dita">mmp

file syntax</xref> and <xref href="GUID-B21141D4-3BFE-59C9-8D5F-147A93BE1C95.dita">Build

tools guide</xref>. </p> </section>

<section id="GUID-64154337-D706-5DE1-9319-4FEA6181EFC4"><title>Architectural

relationships</title> <p>The loader is a server that runs in a separate thread

in the file server process. The loader is built as part of the file server. </p> <p>The

loader server starts when the file server starts. The file server starts after

the kernel is loaded at system start. </p> <p>The loader runs on the user

side, but calls the kernel for services that are not available to general

applications. Examples of services are process creation and code segment creation.

A code segment is an object that represents a piece of code loaded into RAM.

A code segment also represents a piece of code that runs directly from ROM.

The kernel services that the loader uses are protected. The file server process

only is allowed to access these services. </p> <p>The following picture is

an example of program flow. In this example, a client calls <xref href="GUID-25327159-83D6-3507-B187-09EA4BB3727F.dita#GUID-25327159-83D6-3507-B187-09EA4BB3727F/GUID-4F1B2717-D34F-32A4-B6E6-03D0533186A3"><apiname>RLibrary::Load()</apiname></xref>,

which exists in <filepath>euser.dll</filepath>. Internal functions make client-server

calls to the loader server. The loader server code exists in <filepath>efile.exe</filepath>.

The loader server uses kernel services. </p> <fig id="GUID-5FCAE81A-19BC-5BE7-89D2-096A87735381">

<image href="GUID-2735BDAF-295F-5F1E-8925-8F4212D95CD1_d0e264145_href.png" placement="inline"/>

</fig> </section>