How to specify the starting function of a U-boot standalone application.

Hi Guys,

I am writing a u-boot standalone application and are having difficulty understanding how it decides the function to execute when
I used to "go <start addr>+4" command.

In my application I have something like this...

the filename is my_test.c

/* Function prototypes */
int main (int argc, char *argv[]);
void do_func_a (int argc, char *argv[]);
void do_func_info (void);

int main (int argc, char *argv[])

{
    app_startup (argv);

    ....
    do_func_info();

    do_func_a(argc, argv);

    return(0);
}

void do_func_a(int argc, char *argv[])

{
    ....
}

void do_func_info(void)
{

}

When I go go <start addr>, the execution jumps straight to do_func_info() and the application finishes. (which is just a bunch of printf).

How do I ensure that when compiled, the my_test.bin places the main function at the "go" point?

I have tried re-ordering the function bodies around, moving main as the last function and thus removing all the function prototypes. I tried name matching the "main" function to the file name, none seems to help.

Thank you so much for all your help.

Richard Retanubun.

Hi all,

I have the same problem. When I modify the source code the compiler may or may not rearrange the functions. It is not guaranteed, that the main function always starts at the same address.

How can this be solved? Is it possible/meaningful to put the main function into a separate linker segment? Any suggestions?

My temporary solution:
Because I had to patch the U-Boot code, especially the API, anyway for my purposes, I decided to implement my test function as U-Boot command instead as standalone application.

Best Regards,
Jens

The simplest way I've found is to make the following C file:

--- _start.c ---
void _start(void)

{
    extern int main(int argc, char **argv);
    char *args[] = { "myprogramname", "-foo", "bar", /* etc. etc. */ };
    main(sizeof(args)/sizeof(args[0]), args);
    /* Wait forever after the program ends */
    for (;;);
}

-----------------

Then, link '_start.o' before *any* other objects in your link step.

Voila! The text entry should be _start!

Feel free to add BSS initialization, etc. in _start as needed.

Jason McMullan
MTS SW
System Firmware

NetApp

724.741.5011    Fax
724.741.5166    Direct
412.656.3519    Mobile

jason.mcmullan at netapp.com
www.netapp.com

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Hi Jason,

Very nice. Thank you for this tip!

Best Regards,
Jens

Hi Guys,

I found this in the u-boot FAQ (is there anything that thing can't answer? :D)

http://www.denx.de/wiki/view/DULG/MyStandaloneProgramDoesNotWork

Of course, Jason's solution is also nice. Thanks for that!

Regards,

- Richard Retanubun