IDT with C

[OSMAN]

Hello.

Please tell me very well how can I make Interrupt Descriptor Table with C language (and then load it).

[QuiTeVexat]

You do something like this:

Code: Select all

struct idt_entry
{
   uint16 addr_l;
   uint16 sel;
   uint8  nulls;
   uint8  attrib;
   uint16 addr_h;
};

struct idt_entry idt[49];

And then you write a couple of functions to fill the table in with the right values. It's hard to make this one generated at compile/link-time because of the division between the low parts of the address and the high parts, and linkers won't usually do bitmasks and shifts for you.

As for loading, it works like LGDT, you need a pointer structure, so set up a temporary location for that, load it up (like you would for a GDT pointer), and use some inline assembly like so:

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asm("lidt (%0)" ... <fill in the rest here>

[GLneo]

http://www.osdever.net/bkerndev/index.php?the_id
does it vary nicely

[AR]

You do something like this:

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struct idt_entry
{
   uint16 addr_l;
   uint16 sel;
   uint8  nulls;
   uint8  attrib;
   uint16 addr_h;
};

It is important to not forget __attribute__((__packed__)):

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struct idt_entry
{
   uint16 addr_l;
   uint16 sel;
   uint8  nulls;
   uint8  attrib;
   uint16 addr_h;
} __attribute__((packed));

Otherwise each one of those variables will be uint32 regardless of the type.

[JoeKayzA]

Isn't it also neccessary to add

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struct idt_entry idt[49] __attribute__((aligned(4)));

?

AFAIK, the descriptor structures need to be aligned on a 32-bit border.

cheers Joe

[Pype.Clicker]

the compiler is much likely to align *anything* on a 32bits boundary, btw. it even happen to align strings of characters on 32bits boundaries some days.