DOS ain't dead

Hello everyone!

Under FreeDos, i compile programs with GCC, after to have set IDT, remap master & slave ports and blabla... I want load my IDT from lidt asm instruction

For be brief :
idt_pointer.size = 256*sizeof(GateDescriptor) - 1;
idt_pointer.base = (uint32_t)interruptDescriptorTable;
asm volatile("lidt %0" : : "m" (idt_pointer));

From example here by AlgorithMan-de.

My problem.. program crash at the asm inline. I've GDB for be sure (Same problem for lgdt,sgdt,lidt and sidt opcodes) WHY ? I think FreeDos/Dpmi have already loaded GDT and block memory access. I've search DPMI functions for clean previous GDT, and put MY GDT.. I've need of you

I've found docs on http://www.delorie.com/djgpp/doc/libc/
__dpmi_free_ldt_descriptor()
__dpmi_allocate_ldt_descriptors()
but i don't know if it's a good way for me..


Best regards,

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Sébastien FAVIER

ps: Excuse me for my English level, I'm a French student

Maybe one reason is that your DPMI client app runs under ring 3, while DPMI server runs under ring 0 so you cannot change all you want. I think it's not good idea to completly replace IDT. Under DPMI it's complicated because there can happen interrupts in real mode and pmode too so there are 2 ways to handle them. DJGPP provides some DPMI wrappers usefull for hooking your own ISR. I don't remember details...
The __dpmi_allocate_ldt_descriptors() function is good for defining your own segment if you need e.g. some MMIO memory transfer. For IDT stuff there should be similar functions...

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DOS gives me freedom to unlimited HW access.

Thank you RayeR, DPMI client app runs under ring 3 yes exactly.
I will invertigate with __dpmi_allocate_ldt_descriptors()

If someone have ideas or C example with this __dpmi_allocate_ldt_descriptors() his help will be appreciated

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Sébastien FAVIER

ps: Excuse me for my English level, I'm a French student