User Mode

[Jeko]

How can I switch to the ring 3 from ring 0?

[Hery]

You must jump to code segment with privellege level 3. You can do it when you set up TSS. How to set up TSS you can find in Intel Manuals

[earlz]

doing iret is also a good method

[darktemplar]

But you first have to have a TSS, before you do any IRET

[earlz]

i dont have a tss and my iret method works
its called software task switching

[gaf]

Even with software task-swicthing you need at least one TSS per CPU on the IA32 architecture. While you can switch to user-mode without having a TSS, the first call of an interrupt will cause a triple-fualt as the kernel stack pointer can't be determined (Intel reference manual, volume 3: chapter 5.12 - Exception and Interrupt handling).

regrads,
gaf

[darktemplar]

hckr83, I have software task switching in my kernel too, and it requires a TSS =)

[earlz]

hmmm maybe thats why im getting invalid opcode error
after i think about it it seems right that it wouldnt know the kernel stack

[JAAman]

yes -- though it shouldn't cause an invalid opcode error -- infact you could never recieve any error at all -- it would just tripple-fault

you can switch into a ring3 task, but not out of it without the information located in the TSS, so if any exception hard-int, or soft-int occures, whos handler is not in ring3, you will triple-fault

[earlz]

i thought it would gpf

but how can i still display the exception message if i can't go back to ring0

[darktemplar]

Conclusion - get this TSS