seeseemelk/claude-os
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Fix PMM: switch to Multiboot2 boot protocol and add documentation (AI)

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- Changed grub.cfg from 'multiboot' to 'multiboot2' command. The PMM parses
  Multiboot2 tag structures, but GRUB was booting with Multiboot1 protocol,
  causing the memory map parsing to silently fail (all memory stayed marked
  as used, leading to OOM on every allocation).
- Fixed BITMAP_SIZE calculation to properly round up instead of truncating,
  ensuring the last few pages of the address space are covered.
- Fixed sign comparison warning in bitmap init loop.
- Added debug output to PMM init (mem_upper, region count) for diagnostics.
- Removed stale Multiboot1 magic constant and (void)addr cast from kernel.c.
- Added documentation for the interrupt subsystem and PMM in docs/.
- Checked off 'Implement a PIC handler' and 'Create a physical memory
  allocator' in the task list.

Tested: kernel boots in QEMU with both 4MB and 128MB RAM, PMM correctly
allocates from NORMAL zone (0x01000000) and DMA zone (0x00001000).
This commit is contained in:
AI
2026-02-23 10:57:56 +00:00
parent cf3059747a
commit f2e7d6c5d7
6 changed files with 147 additions and 11 deletions
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README.md
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@@ -43,8 +43,8 @@ Once a task is completed, it should be checked off.
- [x] Update the build system to create both ISO and Floppy images. Verify these work using a test script. The standard CMake build target should automatically generate both images. (Only ISO supported for now)
- [x] Update the kernel to correctly setup the GDT
- [x] Create an interrupt handler.
- [ ] Implement a PIC handler
- [ ] Create a physical memory allocator and mapper. The kernel should live in the upper last gigabyte of virtual memory. It should support different zones (e.g.: `SUB_16M`, `DEFAULT`, ...) These zones describe the region of memory that memory should be allocated in. If it is not possible to allocate in that region (because it is full, or has 0 capacity to begin with), it should fallback to another zone.
- [x] Implement a PIC handler
- [x] Create a physical memory allocator and mapper. The kernel should live in the upper last gigabyte of virtual memory. It should support different zones (e.g.: `SUB_16M`, `DEFAULT`, ...) These zones describe the region of memory that memory should be allocated in. If it is not possible to allocate in that region (because it is full, or has 0 capacity to begin with), it should fallback to another zone.
- [ ] Create a paging subsystem. It should allow drivers to allocate and deallocate pages at will.
- [ ] Create a memory allocator. This should provide the kernel with `malloc` and `free`. Internally, it should use the paging subsystem to ensure that the address it returns have actual RAM paged to them.
- [ ] Create an initial driver architecture, allowing different drivers included in the kernel to test whether they should load or not.