Re: [microblaze-uclinux] Note to bootloader developers

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Yashi,

Yasushi SHOJI wrote:

>>A note to the developers of these bootloaders, if you wish to add kernel 
>>command line support, it's easy.  When you jump to the kernel start 
>>address, just have r5 contain the address of a null-terminated string 
>>that is the kernel command line.  This string could live anywhere - 
>>BRAM, flash, doesn't matter. The kernel copies it away safely very early 
>>in the piece, so you don't need to worry about it getting corrupted.
> 
> I have to object on this.
> 
> so as I (as a programmer working on microblaze port; not as an
> employee of Atmark Techno) am an embedded system programmer, what we
> need are:
> 
> 1. standard tag based kernel paramter passing scheme
> 2. compile time parter passing scheme
> 3. (if any one needs it) current string based simple parameter scheme.
> 
> comments welcome!

Feel free to object, and to implement the tag based scheme! :)  I'll 
freely admit that the current approach was a quick hack by myself and 
Brett to get some form of command line params into the kernel. 
Necessity is the mother of invention and all that.

However, from what I saw in the source, basically all the kernel expects 
ultimately is a pointer to a string that it later parses.  So, is your 
objection just the simplistic mechanism for forming that string (ie a 
bootloader issue)?  Or is it something deeper than that, that would go 
into setup_arch()?

 From linux-2.4.x/init/main.c:

asmlinkage void __init start_kernel(void)
{
         char * command_line;
         extern char saved_command_line[];

	...

         setup_arch(&command_line);
         printk("Kernel command line: %s\n", saved_command_line);
         parse_options(command_line);


Regards,

John



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