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entry: copy staged E820 map into .bss memmap_*

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Pierre-Emmanuel Gob. 2026-10-05 18:11:57 +02:00
parent 2a7e411175
commit 51b654d5e3
2 changed files with 66 additions and 1 deletions
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34
include/e820.h Normal file
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/* Nadir BIOS E820 memory-map entry (int 0x15, eax=0xE820).
*
* Staged by the stage-1 boot sector in 16-bit real mode at Ring 0 (CPL 0)
* into low memory (0x5000 count, 0x5020 entries) while BIOS calls still
* work, then copied by the stage-2 entry into the .bss globals
* memmap_count / memmap_entries owned by the PMM. Runs under the
* identity-mapped first 1GB, so physical == virtual addresses here.
* Fault behavior: no IDT exists during staging/copy, so a bad pointer
* triple-faults; the entry count is clamped to E820_MAX on both ends.
*/
#ifndef NADIR_E820_H
#define NADIR_E820_H
#include <stdint.h>
/* Max entries the boot sector stages and the kernel keeps. */
#define E820_MAX 64
/* Usable-RAM type in the E820 type field. */
#define E820_USABLE 1
/* One 24-byte BIOS E820 entry: byte-based [base, base+length) range.
* Preconditions: filled by BIOS int 0x15 or by the boot-sector fallback
* (single type-1 region at 1MB); length may be 0 (ignored by the PMM).
* Failure modes: none in C — a corrupt table only mis-marks frames. */
struct e820_entry {
uint64_t base;
uint64_t length;
uint32_t type;
uint32_t acpi_attr;
} __attribute__((packed));
#endif /* NADIR_E820_H */