50 lines
1.5 KiB
Markdown
50 lines
1.5 KiB
Markdown
# IDT generation and loading
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The IDT management is defined inside `shelter/lib/include/irq/idt.h` and implemented inside `shelter/lib/src/irq/idt.c`. The current IDT generator generate the IDT according to boot process needs, and is therefore not definitive.
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## IDT generation
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The IDT entry is structured with this structure:
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``` C
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#pragma pack(1)
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typedef struct {
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sh_uint16 offset_low;
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sh_uint16 selector;
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sh_uint8 ist;
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sh_uint8 type_attr;
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sh_uint16 offset_mid;
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sh_uint32 offset_high;
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sh_uint32 reserved;
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} sh_idt_IDT_ENTRY;
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#pragma pack()
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```
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The full IDT is stored in this structure:
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``` C
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#pragma pack(1)
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typedef struct {
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sh_idt_IDT_ENTRY entries[256];
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} sh_idt_IDT;
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#pragma pack()
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```
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IDT entries are generated using the following functions:
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- `sh_idt_fill_type_attr_byte(sh_bool present,sh_uint8 dpl,sh_uint8 type)`: generate the `type_attr` byte
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- `sh_idt_fill_idt_entry(sh_uint64 offset,sh_uint16 selector,sh_uint8 ist,sh_uint8 type_attr)`: generate an IDT entry, expect the `type_attr` argument as `sh_idt_fill_type_attr_byte()` would generate it
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The IDT is generated by `sh_idt_fill_idt(sh_idt_IDT *idt)`.
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Using the following structure:
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``` C
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#pragma pack(1)
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typedef struct {
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sh_uint16 limit;
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sh_uint64 base;
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} sh_idt_IDTR;
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#pragma pack()
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```
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`sh_idt_load_idtr(sh_idt_IDT *idt)` load the IDT.
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The following vectors are filled for the moment: 0 to 21, 28 to 30, 32 to 47, 254 and 255. Please see the [IRQ docs](irq.md) to see how the handlers work.
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