Problem with 32bits data segment

[raymond]

Hello,

Since a few weeks I am working on a 32-bits kernel for
the Intel 386+ platform. There's one problem which I cannot
fix in my code. For a better understanding of the code,
I want to tell some specs about my kernel first:

The kernel is in the rdkernel.asm file at
http://rvtsoftware.webslice.nl/krnlproj/

rdkernel.inc is needed too..

The system boots up. The bootloader loads the kernel at address
0050:0000, which is equivalent to address 0000:0500 . So the entry
point of the kernel:

ORG     0x0500

The kernel starts in Intel CPU's real mode.

The kernel sets DS to 0 in an early state. After that, the kernel
changes the values for the GDTR register (which is a memory
operation). After the GDTR register is loaded with the LGDT operation,
a switch to Protected Mode is done by the following operations:


MOV     EAX,    CR0             ; Switch to Protected Mode
OR      AL,     1
MOV     CR0,    EAX

To flush the prefetch queue, a far jump is done to
CODE32_IDX:next . CODE32_IDX is the index for the 32-bits code
segment (4Gb, flat model).

DATA32_IDX is the index for the data segment. And here lies the
bug: This segment seems to be protected, because the system crashes
at the following operation:

mov     BYTE [DS:ESI], 'R'


I looked at the 'flags' byte in the 'data32_desc' descriptor,
but they seem okay. What could be the problem?

[rverma]

HOW DOES YOUR DISCRIPTOR LOOK LIKE?

[raymond]

Hello,

The descriptor for the 32-bits data segment looks like this:

data32_desc     dw      0xFFFF           ; 4 Gb data segment
                dw      0x0
                db      0x0
                db      0x92
                db      0xCF
                db      0

Somehow I fixed this bug. It seems that the far jump to CODE32_IDX:next
didn't work right. I changed it to 'jmp $+2' and the segment seem to work.
I think this is a strange kind of bug...