command line parameters

Till Straumann strauman at
Wed Sep 19 15:02:52 UTC 2007

IIRC, GRUB stores the command line at physical address 0x2000
which (again, IIRC) is not touched by RTEMS so you can do the
ugly trick:

const char *grub_cmdline_hack = (const char *)0x2000;

Beware, it is probably not \0 terminated and I don't remember
if it is an 'official' feature...

I don't remember if GRUB supports multiboot. A cleaner method
lets early BSP startup code use info from the multiboot record
(small mod to start.S and bspstart.c required). This works for me
in combination with etherboot. I can provide a patch if anyone is

-- Till

Joel Sherrill wrote:
> nir levy wrote:
>> Hi All,
>> I am running RTEMS on QEMU emulator and i am using grub for booting ( 
>> similar to most descriptions on the net for doing so).
>> However, i could not find a way to send command line parameters for the 
>> RTEMS applications i am running.
>> I have tried to specified them in the GRUB configuration file ( after 
>> the program name) but they don't seem to be pass to the application in 
>> the Init procedure ( i have checked the c_rtems_main and the procedure 
>> in the boot_card and they don't get there as well). I assume the problem 
>> might be in the grub but if anyone ever succeed doing it and can help me 
>> with that or advice on the issue it will be nice.
> There is no main() in an RTEMS application.  So the idea of
> what to do with command line parameters is a bit vague.
> Some boot loaders pass in a pointer to a data structure which
> is used by the BSP.  U-Boot comes to mind in this case.
> Right now, it is the responsibility of the BSP early start
> code (usually named start.S) to invoke boot_card() with
> argc, argv, and environ.  Right now, this information disappears
> in boot_card() because there is no defined way to make it
> available to the application.
> I looked at this a while back and didn't have any real
> example invoking environments to test with so left it
> alone.  My thoughts were:
> + conditional compile argc, argv support in bootcard.c
>     since it is unused baggage for most BSPs.  BSPs which
>     want to and can support argc, argv can enable it.
> + Define a set of public variables which are the
>    bsp or boot argc, argv, and environ values.
> Getting the info from grub to pc386's start code
> and to boot_card() makes it possible to address the
> more general issue of what to do with them when they
> are available.
> I hope this has encouraged you to modify the BSP
> to transfer the info from grub through start.S to
> boot_card and help define the mechanism. :-D
> FWIW another way I have seen is to prompt a user
> for command line arguments.  Then convert that
> string into argc/argv format to pass into a
> main that was renamed to XXX_main().  This is a
> relatively painless way to port UNIX main()'s to
> RTEMS especially for testing purposes.  I am
> thinking that since at least ttcp has code already
> to do this and I have copied it at least once, that
> is makes sense to generalize it and make it
> part of libmisc.
> --joel
>> Thanks in advance.
>> Best,
>> Nir
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