General Principles

In order to compile and link an application, the following information is needed:

• The header files and compilation flags

• The program entry point

• The libraries to be linked with the program according to the services used by the application, the environment present on the target system, and the actor type (user or supervisor)

Program Entry Point

In order to initialize the libraries correctly before starting the execution of the application code, the program entry point must be set to _start. After the initialization of libraries is completed, _start calls the _main routine which initializes variables in C++ programs. The main() routine is then called.

The _main routine manages any double calling at program initialization; some C++ compilers force a call to _main at the beginning of main().

Depending on the development system, it may be necessary to use specific linker directives to force the linker to extract the _start and _main routines from the libraries.

Libraries

In order to choose which ChorusOS operating system libraries to use, the following points need to be considered:

• Which APIs are used by the application program. For example, a program using the mathematical API has to be linked with the libm.a library.

• What type of system is running on the target. For example, the librpc.a library cannot be used if you are using the basic environment and no additional features.

• The address space in which the program will execute. For example a program loaded as a user extended actor must be linked with the libcx.a library.

Supervisor Actor Binaries

As supervisor actors share the same supervisor address space, they are built as relocatable binaries, leaving the choice of the final link addresses to either the system configuration utility building the system image (for the basic environment) or the Actor Manager (for the extended environment).

Care must be taken when programming supervisor actors: no memory protection is provided between supervisor actors. A badly written supervisor actor accessing addresses outside its own address space can corrupt any supervisor region and cause unexpected behavior such as a system crash or reboot.

User Actor Binaries

User actors are also built as relocatable binaries, even though they use private address spaces. The link address of the user actors and the size of the user address space are board dependent. For a given board, all user actors are linked at the same address.

The final link is done by the Actor Manager when actors are loaded dynamically on the target.