Linux boot

[Silverhawk]

Does someone know why the linux boot reallocates itself from 0x7c00 to 0x90000 ?

I really don't understand...

thanks !

[Silverhawk]

Now, I have another question !

This is a quote frome the linux bootsect.S :

! ok, we've written the message, now
! we want to load the system (at 0x10000)

   mov   ax,#SYSSEG
   mov   es,ax   ! segment of 0x010000
   call   read_it
   call   kill_motor
   call   print_nl

We aren't in Pmode !!! How is it possible to load the system at physical address 0x100000 ???

I really don't understand too...

[Therx]

it isn't 0x100000 but 0x10000

[Silverhawk]

Yes, but a segment of 0x10000 gives a physical address of 0x100000 ??

[Therx]

Sorry I may be wrong as I havn't done much in real mode addressing but the solution may be this:-

I know that somehow 16bit addresses allow you to access just over 1mb (look through the boot sector topics from a while ago) and if the code copied there is small then it may work.

Just a guess

Pete

[Silverhawk]

Thanks Pete !

I will look after it...

[Pype.Clicker]

Yes, but a segment of 0x10000 gives a physical address of 0x100000 ??

you may not have a segment of 0x10000 as the ES register is only 16bits wide.

Code: Select all

@asm-i386/boot.h:
#define DEF_SYSSEG      0x1000

@boot/setup.S
SYSSEG   = DEF_SYSSEG           # 0x1000, system loaded at 0x10000 (65536).

so the actual ES value is 0x1000, which means the logical address 0x10000 will be used.

for sure linux comments could be less confuse here.

[Silverhawk]

OK you're right !
I've read the code with more attention, and indeed, we're at physical address 0x10000...

I 've believe what the comments...

Thanks Pype.Cliker