Re: Changing kernel entry point

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

To follow up on this.

I made my bootloader MULTIBOOT compliant. At the end of "my" boot2, I 
have C code in which I create the MIS structure, push the magic number 
into EAX and the address of the MIS into EBX.

Now I have the following problem. I am not sure what to call from here? 
Should I just jump to location 0x100000 and execute from there (while 
having EAX and EBX set correctly)?

Thanks,
--Martin

On 02/21/2013 10:15 AM, Martin Osterloh wrote:
> Anyone an idea on this?
>
> On 02/19/2013 12:39 PM, Martin Osterloh wrote:
> > [ 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