Salut.
Am fost curios sa vad cum se face procedura de initializare a kernelului
dupa ce e incarcat de loader. (ma rog, pentru i386)
M'am uitat prin /usr/src/linux/arch/i386/boot/setup.S, e chiar haios ce e
pe acolo :) dar la un moment dat mi s'a "rupt filmul" ... Mai precis la
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# Well, that certainly wasn't fun :-(. Hopefully it works, and we don't
# need no steenking BIOS anyway (except for the initial loading :-).
# The BIOS-routine wants lots of unnecessary data, and it's less
# "interesting" anyway. This is how REAL programmers do it.
#
# Well, now's the time to actually move into protected mode. To make
# things as simple as possible, we do no register set-up or anything,
# we let the gnu-compiled 32-bit programs do that. We just jump to
# absolute address 0x1000 (or the loader supplied one),
# in 32-bit protected mode.
#
# Note that the short jump isn't strictly needed, although there are
# reasons why it might be a good idea. It won't hurt in any case.
movw $1, %ax # protected mode (PE) bit
lmsw %ax # This is it!
jmp flush_instr
flush_instr:
xorw %bx, %bx # Flag to indicate a boot
xorl %esi, %esi # Pointer to real-mode code
movw %cs, %si
subw $DELTA_INITSEG, %si
shll $4, %esi # Convert to 32-bit pointer
# NOTE: For high loaded big kernels we need a
# jmpi 0x100000,__KERNEL_CS
#
# but we yet haven't reloaded the CS register, so the default size
# of the target offset still is 16 bit.
# However, using an operand prefix (0x66), the CPU will properly
# take our 48 bit far pointer. (INTeL 80386 Programmer's Reference
# Manual, Mixing 16-bit and 32-bit code, page 16-6)
.byte 0x66, 0xea # prefix + jmpi-opcode
code32: .long 0x1000 # will be set to 0x100000
# for big kernels
.word __KERNEL_CS
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(si e chiar interesant ca vad ca si Linus face wrap la 75 coloane :) )
E clar ca ".byte 0x66, 0xea" e un "jmp far" pe 32 biti si e necesar ca sa
incarce si registrul %cs. Dar de fapt unde sare kernelul aici? Sa inteleg
ca intr'un modul compilat dintr'o sursa de C ? Dar care?
Din /usr/src/linux/init/main.c de ex. ?
Stie cineva? :)
Bogdan Marinca
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