Re: Changing kernel entry point

[Martin Osterloh <martin.osterloh%dartmouth.edu@localhost>]

[ Please find the previous correspondence below this email I forgot to 
include the mailing list]

--------

Thanks for the document. I've been reading it and I understand more and 
more how the BSD bootloader works. I am getting closer.

One thing you mentioned in your article is that the kernel maps itself 
at a very hogh location (0xC0100000 and higher).
Since the BL cannot address anything like that, the physical location 
will be 0x100000 (1MiByte) - right after the BIOS. That makes sense to me.

However, a readelf -x -t -s -d netbsd shows me the following (just the top)

netbsd:     file format elf64-x86-64
netbsd
architecture: i386:x86-64, flags 0x00000112:
EXEC_P, HAS_SYMS, D_PAGED
start address 0xffffffff80100000

Program Header:
    LOAD off    0x0000000000100000 vaddr 0xffffffff80100000 paddr 
0xffffffff80100000 align 2**20
         filesz 0x0000000000265e88 memsz 0x0000000000265e88 flags r-x
    LOAD off    0x0000000000366000 vaddr 0xffffffff80466000 paddr 
0xffffffff80466000 align 2**20
         filesz 0x0000000000040598 memsz 0x00000000000ade80 flags rw-


I am confused as to why the paddr is set to 0xffffffff80100000? 
Shouldn't that be 0x100000? That is actually what causes trouble for me.

I found that KERNBASE, KERNTEXTOFF, etc. are all defined in 
/usr.src.sys.arch.amd64.compile/CUSTOM/machine/param.h (whereas CUSTOM 
is the name of my configuration).
The next thing that came to my mind is that if I change it here I might 
be able to change the physical entry point. Unfortunately, I messed up 
the memory map and locore.S is complaining during the compilation process.

So I guess, I am wondering why the paddr attribute in the elf file is 
not set to 0x100000? And there must be another way to adjust these 
parameters (KERNBASE, KERNTEXTOFF, etc.)?


Again, I truly appreciate your help and advise.

Regards,
Martin

On 02/15/2013 12:11 PM, Julio Merino wrote:
> On Fri, Feb 15, 2013 at 11:29 AM, Martin Osterloh
> <martin.osterloh%dartmouth.edu@localhost> wrote:
> > Hi Julio,
> >
> > Thanks a lot for your quick response!
> >
> > My bootloader is currently very simple (two stages like the BSD bootloader).
> > At the end of boot2 it kicks off my micro-kernel in long mode. I think I
> > will have to change this since the entry point is 32 bit.
> >
> > Could you please point out what/where these data structures are? I am
> > browsing the source tree at the moment and am trying to figure out at which
> > point the elf binary is being loaded. From there on I would back trace to
> > see what the BL does before loading the binary.
> Look for "bootinfo" in the code and in filenames. It has been a long
> time since I touched this code, so I don't remember the specific
> details.
>
> You might also find this useful:
> http://onlamp.com/pub/a/bsd/2007/03/01/inside-multiboot.html