Trying to execute code outside RAM?

[Lionel]

Hello!
My kernel, Chronos, was enabling interrupts, and crashed qemu with the message "Trying to execute code outside RAM or ROM at 0x000000006a006afa".
This address is never defined in my code, so the only clue I have is that it's in the irq code (It works fine with normal interrupts)
This is the output from qemu:

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qemu: fatal: Trying to execute code outside RAM or ROM at 0x000000006a006afa

EAX=00103000 EBX=00010000 ECX=000b82a4 EDX=000703d5
ESI=00000000 EDI=00000000 EBP=0007fef0 ESP=0007fecc
EIP=6a006afa EFL=00200002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00cf9a00 DPL=0 CS32 [-R-]
SS =0010 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     00104040 00000027
IDT=     00104080 000007ff
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000008 CCD=00103000 CCO=LOGICB  
EFER=0000000000000000
FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80
FPR0=0000000000000000 0000 FPR1=0000000000000000 0000
FPR2=0000000000000000 0000 FPR3=0000000000000000 0000
FPR4=0000000000000000 0000 FPR5=0000000000000000 0000
FPR6=0000000000000000 0000 FPR7=0000000000000000 0000
XMM00=00000000000000000000000000000000 XMM01=00000000000000000000000000000000
XMM02=00000000000000000000000000000000 XMM03=00000000000000000000000000000000
XMM04=00000000000000000000000000000000 XMM05=00000000000000000000000000000000
XMM06=00000000000000000000000000000000 XMM07=00000000000000000000000000000000

The link to the code is in my sig (in the dev branch)
Thanks,
Lionel

[VolTeK]

No one should have to click the link to solve your problem. Use the debugger.

[Lionel]

Debugger? Do you mean gdb? I could never get it to work with qemu...

[bubach]

Try bochs and it's internal debugger.

[Lionel]

Also could never get bochs to work.
Maybe developing on a prerelease version of Ubuntu was a bad thing...

[gerryg400]

I'll give you a clue.

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EIP=6a006afa

If you reverse the contents of the EIP you get

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EIP=fa6a006a

If you then pass that through a disassembler you get

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    cli
    push  0
    push  ...

[gravaera]

Yo:

One of the few core basics of getting a kernel to run is to ensure that the CPU is executing the code in the first place...

[assembler01]

I had the same problem with my bootloader and it turned out to be a segmentation problem, so maby that is what it is.
PS: This is my first post.

[bubach]

Also could never get bochs to work.

This is my bochsrc.bxrc (just trial&error on my part with some googling to get this working with bochs 2.5.1)

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# configuration file generated by Bochs
#plugin_ctrl: unmapped=1, biosdev=1, speaker=1, extfpuirq=1, gameport=1, pci_ide=1, acpi=1, ioapic=1
config_interface: win32config
display_library: win32
megs: 32
#romimage: file="C:\Program\Bochs-2.5.1\BIOS-bochs-latest"
#vgaromimage: file="C:\Program\Bochs-2.5.1\VGABIOS-lgpl-latest"
boot: floppy
floppy_bootsig_check: disabled=0
magic_break: enabled=1
floppya: type=1_44, 1_44="a:", status=inserted
# no floppyb

and I use real floppies or mount a 1.44mb image file with the program ImDisk:
http://www.ltr-data.se/opencode.html/#ImDisk

[assembler01]

If you look at the segment registers you can see that cs is different from all the other segment regs, so you can try loading your segment regs with this:

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mov ax, cs
mov ds, ax
mov ss, ax
mov fs, ax
mov gs, ax

[gerryg400]

CS should be different from the other segment regs.

Since the hint didn't work ...

The bug is here, in descriptor_tables.c line 25

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//Apparently, I have to extern IRQ's
extern u32int irq0;

[assembler01]

But if you have a bootloader then cs is 07C0h, right?

[gerryg400]

Chronos boots from Grub I think. So it's already in protected mode.

[Combuster]

The effect of Segmentation is different in Protected Mode compared to Real Mode.

Also, you're hijacking someone else's thread. It's better that you refrain from posting than to just guess because wrong information isn't helping anyone. If you don't understand something, will you please make a new thread so we can help you instead of fencing you out like paparazzi.

[Lionel]

I had to externalize the irqs because they wouldn't be recognized by C.
Also, I don't get what your saying with line 25, what's wrong with it? I have a feeling its the type.