[U-Boot-Users] How to specify the starting function of a U-boot standalone application.

[U-Boot-Users] How to specify the starting function of a U-boot standalone application.

[richardretanubun]

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.

[U-Boot-Users] How to specify the starting function of a U-boot standalone application.

[Jens Gehrlein]

Hi all,

richardretanubun schrieb:
> 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.

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

[U-Boot-Users] How to specify the starting function of aU-boot standalone application.

[McMullan, Jason]

On Wed, 2008-06-25 at 07:44 +0200, Jens Gehrlein wrote:
> 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?

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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[U-Boot-Users] How to specify the starting function of aU-boot standalone application.

[Jens Gehrlein]

Hi Jason,

McMullan, Jason schrieb:
> On Wed, 2008-06-25 at 07:44 +0200, Jens Gehrlein wrote:
>> 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?
> 
> 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.

Very nice. Thank you for this tip!

Best Regards,
Jens

[U-Boot-Users] How to specify the starting function of aU-boot standalone application.

[richardretanubun]

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

Jens Gehrlein wrote:
> Hi Jason,
>
> McMullan, Jason schrieb:
>> On Wed, 2008-06-25 at 07:44 +0200, Jens Gehrlein wrote:
>>> 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?
>>
>> 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.
>
> Very nice. Thank you for this tip!
>
> Best Regards,
> Jens