Calculating my flags for an idt entry

[cjhawley001]

I have this code in place to get the flags for an IDT entry:

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idt[num].flags = (TYPE_ATTRIB | (dpl << DPL_SHIFT) | gate_type);

It works when my values for TYPE_ATTRIB = 0x80, dpl = 0x0 and gate_type = 0xE

But it also works if i change my dpl outside of the 0-3 zone.

Is my formula to get my flag right?

I have looked at tutorials but they all just have pre defined flags...

Chris

[Tomaka17]

If you set the DPL to 4, it will be 100, the 1 being thus considered as something else in the entry

I recommend using a structure with a variable for each bit
This is mine:

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typedef struct IDTEntry {
	u16 loffset;
	u16 segment;
	int notsetA:1;	// always set to 0
	int trap:1;		// if 0, there will be an automatic "cli" on interrupt
	int setA:1;		// always set to 1
	int setB:1;		// always set to 1
	int bits32:1;
	int notsetB:1;	// always set to 0
	int dpl:2;
	int present:1;
	u16 hoffset;
} __attribute__((packed)) IDTEntry;

Note that this is only for 32 bits
You can certainly improve this structure with like:

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struct {
	...
	#ifdef _64BITS_
	u32 hhoffset;
	#endif
}

[neon]

I recommend using a structure with a variable for each bit

Please take note that the format of bit fields are undefined by the standard. This is my primary argument against using them.

[cjhawley001]

Should I just do some checking to make sure values are legal?

Chris