t3hn3rd
2d190c221a
Introduce boot.mgr - a self-registering, dependency-ordered boot initialization framework with barrier-based phasing and glob pattern matching. Units now declare their own init procedures and dependencies via registerBoot()/registerBarrier() in their initialization sections, boot.mgr.run() topologically sorts and executes them. - Add src/boot/boot.mgr.pas with topoSort, glob matching, barrier two-pass algorithm, and boot tree printer - Gut src/asuro.pas (kmain): now just stores multiboot info, calls System.init(), boot.mgr.run, and yield() - Add initialization sections with registerBoot() to 53 existing units - Add new units: core.pas, test.pas, driver.storage.boot.pas, app.wasm.pas, app.bsod.pas (factored out of asuro.pas) - Define 9 barrier phases: immediate -> early -> middle -> storage -> bus -> device -> bus.late -> late -> final - Fix xHCI ISR: exclude PRC/WRC from PORTSC change bit clearing to prevent race with port reset busy-wait - Fix driver.bus.usb.core fire_completion_hooks: guard against uint32 underflow when CompletionHookCount = 0 - Move auto_mount_volumes from device barrier to late barrier so it runs after PCI scan discovers storage controllers - Add toolchain/compile_initcalls.sh for boot entry extraction - Add Boot Registration sections to all 51 doc files; create 4 new doc files; rewrite boot.mgr.md; update mkdocs.yml nav
119 lines
3.6 KiB
Markdown
119 lines
3.6 KiB
Markdown
# arch.x86.gdt
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Global Descriptor Table (GDT) data structures, gate management, and loading.
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## Overview
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This unit defines the GDT data structures and provides procedures to set individual segment descriptors, flush the GDT into the CPU via LGDT, and reload it after modification. During `init`, five standard descriptors are installed: a null segment, a ring-0 code segment, a ring-0 data segment, a ring-3 code segment, and a ring-3 data segment. The GDT can hold up to 1024 entries; the GDT pointer limit is updated automatically as new gates are added.
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## Dependencies
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- `io.syslog`
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## Boot Registration
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Registered with `boot.mgr` as `arch.x86.gdt` at the `early` barrier.
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## Types
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### TGDT_Entry / PGDT_Entry
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```pascal
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TGDT_Entry = packed record
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limit_low : uint16;
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base_low : uint16;
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base_middle : uint8;
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access : uint8;
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granularity : uint8;
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base_high : uint8;
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end;
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```
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An 8-byte x86 segment descriptor in the standard hardware layout.
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| Field | Description |
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|--------------|-------------|
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| limit_low | Lower 16 bits of the segment limit |
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| base_low | Lower 16 bits of the segment base address |
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| base_middle | Bits 16–23 of the segment base address |
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| access | Access byte: present, DPL, type flags |
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| granularity | Upper 4 bits of limit plus granularity/size flags |
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| base_high | Bits 24–31 of the segment base address |
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### TGDT_Pointer
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```pascal
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TGDT_Pointer = packed record
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limit : uint16;
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base : uint32;
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end;
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```
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The 6-byte structure passed to the LGDT instruction. `limit` is the byte size of the GDT minus one; `base` is the linear address of the first GDT entry.
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## Variables
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### gdt_entries
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```pascal
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var gdt_entries : array[0..1023] of TGDT_Entry;
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```
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Static array holding up to 1024 GDT descriptors.
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### gdt_pointer
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```pascal
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var gdt_pointer : TGDT_Pointer;
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```
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The LGDT operand. `base` is set to the address of `gdt_entries`; `limit` grows as gates are added.
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## Functions and Procedures
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### init
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```pascal
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procedure init();
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```
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Initialises the GDT with five standard entries and calls `flush` to load it:
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| Gate | Offset | Access | Description |
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|------|--------|--------|-------------|
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| 0 | 0x00 | 0x00 | Null descriptor |
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| 1 | 0x08 | 0x9A | Ring-0 code (execute/read, 4 GB flat) |
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| 2 | 0x10 | 0x92 | Ring-0 data (read/write, 4 GB flat) |
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| 3 | 0x18 | 0xFA | Ring-3 code (execute/read, 4 GB flat) |
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| 4 | 0x20 | 0xF2 | Ring-3 data (read/write, 4 GB flat) |
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### set_gate
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```pascal
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procedure set_gate(Gate_Number : uint32; Base : uint32; Limit : uint32; Access : uint8; Granularity : uint8);
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```
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Writes a single GDT descriptor at index `Gate_Number`. Splits `Base` and `Limit` across the appropriate fields of the `TGDT_Entry` record. Automatically updates `gdt_pointer.limit` if the new gate extends beyond the current table boundary.
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### flush
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```pascal
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procedure flush;
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```
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Loads the GDT via LGDT and reloads all data segment registers (DS, ES, FS, GS, SS) with selector 0x10 (ring-0 data). A far jump to selector 0x08 (ring-0 code) flushes the instruction pipeline and reloads CS.
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### reload
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```pascal
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procedure reload;
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```
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Reissues LGDT without touching segment registers. Used after adding descriptors such as a TSS when the existing segment mappings remain valid.
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## Notes
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- The far jump in `flush_gdt` is hand-assembled using `db`/`dw` directives because the Free Pascal inline assembler does not support far-jump syntax directly.
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- Gates are numbered from 0; the segment selector for gate N is N * 8 with the lower 3 bits encoding the requested privilege level.
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- The table supports up to 1024 descriptors (8 KiB), which is the hardware maximum for a 32-bit protected-mode GDT.
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