SLAU132 User guide

SLAU132Y September 2004 – June 2021

2.6 Passing Arguments to main()

Some programs pass arguments to main() via argc and argv. This presents special challenges in an embedded program that is not run from the command line. In general, argc and argv are made available to your program through the .args section. There are various ways to populate the contents of this section for use by your program.

To cause the linker to allocate an .args section of the appropriate size, use the --arg_size=size linker option. This option tells the linker to allocate an uninitialized section named .args, which can be used by the loader to pass arguments from the command line of the loader to the program. The size is the number of bytes to be allocated. When you use the --arg_size option, the linker defines the __c_args__ symbol to contain the address of the .args section.

It is the responsibility of the loader to populate the .args section. The loader and the target boot code can use the .args section and the __c_args__ symbol to determine whether and how to pass arguments from the host to the target program. The format of the arguments is an array of pointers to char on the target. Due to variations in loaders, it is not specified how the loader determines which arguments to pass to the target.

If you are using Code Composer Studio to run your application, you can use the Scripting Console tool to populate the .args section. To open this tool, choose View > Scripting Console from the CCS menus. You can use the loadProg command to load an object file and its associated symbol table into memory and pass an array of arguments to main(). These arguments are automatically written to the allocated .args section.

The loadProg syntax is as follows, where file is an executable file and args is an object array of arguments. Use JavaScript to declare the array of arguments before using this command.

loadProg(file, args)

The .args section is loaded with the following data for non-SYS/BIOS-based executables, where each element in the argv[] array contains a string corresponding to that argument:

Int argc;
Char * argv[0];
Char * argv[1];
...
Char * argv[n];

For SYS/BIOS-based executables, the elements in the .args section are as follows:

Int argc;
Char ** argv;    /* points to argv[0] */
Char * envp;     /* ignored by loadProg command */
Char * argv[0];
Char * argv[1];
...
Char * argv[n];

For more details, see the "Scripting Console" page.