grub problems

[beyondsociety]

I am trying to get my kernel to be moved to virtual address 4MB and yet have it loaded at the 1MB physical.

I wrote some basic code to move my kernel to a higher place and it was working fine with grub. But now grub errors out because the load address is below 1 meg and grub doesnt support that.

The funny thing is it was working before. There are two possibilites to my problem.
[*] it isnt loaded at 1MB or above, but Ive checked this.
[*] if you load it to a really high address like 0xC0000000, it will overflow because I guess your trying to access memory thats not there.

I believe my problem lies with the second possibility. Could I be correct? How can I get around this?




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[Tim]

I think this is the problem:

Code: Select all

        ; fields used if MULTIBOOT_AOUT_KLUDGE is set in MULTIBOOT_HEADER_FLAGS
        dd mboot                       ; These are PHYSICAL addresses
        dd kernel_code                 ; Start of kernel .text (code) section
        dd kernel_data                 ; End of kernel .data section
        dd kernel_end                  ; End of kernel BSS
        dd _start                      ; Kernel entry point (initial EIP)

Look at your own comment: these are PHYSICAL addresses. A symbol like 'mboot' or 'kernel_code' is a virtual address; if you look in the disassembly, you should find that these symbols are located above 4MB.

You need to translate each symbol's virtual address to the corresponding physical address, for example: (I think this is from the GRUB sample kernel)

Code: Select all

#define V2P(x)      ((x) - ADDR_KERNEL_VIRT + ADDR_KERNEL_PHYS)
   /* header_addr */
   .long   V2P(_multiboot_header)
   /* load_addr */
   .long   ADDR_KERNEL_PHYS
   /* load_end_addr */
   .long   V2P(__end__)
   /* bss_end_addr */
   .long   V2P(__bss_end__)
   /* entry_addr */
   .long   V2P(_KernelEntry)

(apologies for the AT&T syntax but hopefully you get the idea)

[beyondsociety]

Ok, Ive fixed that problem and have added paging code. I have finaly gotten it to compile and when I went to test it on Grub, it reports: selected item cannot fit into memory.
I looked at the grub documentation and this is what is says

28 : Selected item cannot fit into memory
This error is returned if a kernel, module, or raw file load command is either trying to load its data such that it won't fit into memory or it is simply too big.

Does anybody know what could be causing this? Is there a workaround?

Thanks in advance.

[Pype.Clicker]

iirc, this error is often thrown because the target load address of your file is too high (GRUB is trying hard to put your file at *physical* 0xC000_0000 ...)

[beyondsociety]

iirc, this error is often thrown because the target load address of your file is too high (GRUB is trying hard to put your file at *physical* 0xC000_0000 ...)

Even though I have loaded it at 0x40000000 which is 1GB. I guess I'll try a lower address.

[Pype.Clicker]

i guess we should put this in the FAQ: it's always coming back ...

[beyondsociety]

You could add this if you like. It didnt work for me but it might work for someone else.

Selected item cannot fit into memory
Selected item cannot fit into memory1