moving kernel code to kernel/
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-5
@@ -9,7 +9,7 @@ reboot is miserable.
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This is the machinery that catches those faults and prints what happened instead.
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It's all x86_64-specific, so it lives behind the [arch](arch.md) boundary in
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`src/arch/x86_64/`. Only the 32 CPU-defined exception vectors are wired up so far;
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`src/kernel/arch/x86_64/`. Only the 32 CPU-defined exception vectors are wired up so far;
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device interrupts (timer, keyboard, via the APIC) come later, on the same IDT.
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## First the GDT
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@@ -20,7 +20,7 @@ IDT gate names a code-segment *selector* that must resolve in the current GDT. T
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firmware left a GDT in place, but we don't control it, so we install our own with
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known selectors: `0x08` kernel code, `0x10` kernel data.
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`src/arch/x86_64/gdt.zig` holds three flat descriptors — a required null entry,
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`src/kernel/arch/x86_64/gdt.zig` holds three flat descriptors — a required null entry,
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plus code and data — where the only bits that matter in long mode are the access
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byte and the code segment's long-mode (`L`) flag. Loading it (`gdt_flush` in
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`isr.s`) does two things: `lgdt`, then reload the segment registers. The data
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@@ -33,7 +33,7 @@ into CS:RIP.
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The **Interrupt Descriptor Table** maps each of 256 vectors to a handler. Each
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entry is a 16-byte *gate* holding the handler's address (split across three
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fields, a quirk of the format), the code selector (`0x08`), and flags: `0x8E`
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means present, ring 0, 64-bit interrupt gate. `src/arch/x86_64/idt.zig` builds the
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means present, ring 0, 64-bit interrupt gate. `src/kernel/arch/x86_64/idt.zig` builds the
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table, points the first 32 vectors at their stubs, and loads it with `lidt`
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(`idt_flush`).
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@@ -49,7 +49,7 @@ hit a fault *while trying to deliver another fault* — very often because the
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current stack pointer is bad, so pushing the exception frame itself faulted. If
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the #DF handler then tried to push onto that same bad stack, it would fault a
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third time and **triple-fault** — an instant reset. So the #DF gate is pointed at
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**IST1**, a small dedicated stack (`src/arch/x86_64/tss.zig`) that's always valid.
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**IST1**, a small dedicated stack (`src/kernel/arch/x86_64/tss.zig`) that's always valid.
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Bringing it up: fill in the TSS's IST1 pointer, publish the TSS through a
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descriptor in the GDT (`gdt.setTss`), and load it into the task register with
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@@ -60,7 +60,7 @@ which is why the GDT grew from three entries to five.
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On an exception the CPU pushes a small frame (SS, RSP, RFLAGS, CS, RIP) and, for
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*some* vectors, an **error code**. That inconsistency is a nuisance, so each stub
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in `src/arch/x86_64/isr.s` normalises it: vectors that don't get a hardware error
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in `src/kernel/arch/x86_64/isr.s` normalises it: vectors that don't get a hardware error
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code push a dummy `0`, then every stub pushes its **vector number** and jumps to a
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shared tail, `isr_common`. The tail pushes all the general registers and calls the
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Zig handler with a pointer to the whole thing.
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