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kernel: load at 16 MB, clear of what firmware keeps low

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From 1 MB the 34 MB kernel ran across 8 MB, where OVMF keeps ACPI NVS
memory that outlives the firmware -- so it was overwritten on every
boot, after ExitBootServices. Firmware leaves its leftovers low; above
16 MB is where a machine is most reliably empty.

KERNPHYS in memlayout.h, and kernel.ld agreeing with it. Nothing else
named the old address. Under OVMF the range is now only boot-services
memory: staged, copied home after the firmware exits, no warning. Boots
as a CD and as a USB disk, 1 and 4 CPUs.

The 15 MB below the kernel is not given to the page allocator yet.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
This commit is contained in:
Nexoniarz 2026-10-24 00:13:53 +02:00
commit 5ed8f1b0d5
4 changed files with 14 additions and 5 deletions
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2
boot/uefi/main.c
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@ -594,7 +594,7 @@ place_staged(void)
}
// Load PT_LOAD segments to p_paddr. Physical addresses, not virtual: the
// kernel is linked at 0xffff800000100000 but must be *placed* at 0x100000, and
// kernel is linked at 0xffff800001000000 but must be *placed* at 0x1000000, and
// p_paddr is where the linker script says each segment belongs.
static UINT64
load_elf(EFI_FILE_PROTOCOL *file)