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BL: Query and store e820 memory map

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- bl stage 1: move gdt+pm setup to stage 2 (avoids mode switching)
- bl stage 2: at entry query e820 table from bios, then setup gdt+pm
- kernel/memmap: pad map entry to 24 bytes, as exported by bl
- kernel/memmap: map copy (gbowne1)
- Makefile: facilitate placing the memory map at a known location
- Update bl docs
This commit is contained in:
vmttmv
2026-01-15 21:39:53 +02:00
parent f572101d6b
commit 4fa82854dd
6 changed files with 98 additions and 53 deletions
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9
Makefile
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@@ -8,8 +8,13 @@ OBJCOPY = i386-elf-objcopy
BUILD_DIR = build
CROSS_DIR = cross
DISK_IMG = $(BUILD_DIR)/disk.img
STAGE2_ADDR = 0x7e00
STAGE2_SIZE = 2048
# Place the memory map (e820) past stage2 bl in memory
MEMMAP_BASE = $(shell echo $$(($(STAGE2_ADDR) + $(STAGE2_SIZE))))
KERNEL_C_SRC = $(wildcard kernel/*.c)
KERNEL_ASM_SRC = $(wildcard kernel/*.asm)
KERNEL_OBJ = $(patsubst kernel/%.c, $(BUILD_DIR)/%.o, $(KERNEL_C_SRC))
@@ -29,7 +34,7 @@ stage1: $(BUILD_DIR)
# NOTE: Stage2 final size should be checked against `$(STAGE2_SIZE)` by the build system to avoid an overflow.
# Alternatively, convey the final stage2 size through other means to stage1.
stage2: $(BUILD_DIR)
$(AS) $(ASFLAGS) -o $(BUILD_DIR)/stage2.o bootloader/stage2.asm
$(AS) $(ASFLAGS) -DMEMMAP_BASE=$(MEMMAP_BASE) -o $(BUILD_DIR)/stage2.o bootloader/stage2.asm
$(CC) -std=c11 -ffreestanding -nostdlib -nostdinc -fno-stack-protector -m32 -Iklibc/include -g -c -o $(BUILD_DIR)/stage2_load.o bootloader/stage2_load.c
$(LD) -Tbootloader/stage2.ld -melf_i386 -o $(BUILD_DIR)/$@.elf $(BUILD_DIR)/stage2.o $(BUILD_DIR)/stage2_load.o
$(OBJCOPY) -O binary $(BUILD_DIR)/$@.elf $(BUILD_DIR)/$@.bin
@@ -39,7 +44,7 @@ $(BUILD_DIR)/asm_%.o: kernel/%.asm
$(AS) $(ASFLAGS) -o $@ $<
$(BUILD_DIR)/%.o: kernel/%.c
$(CC) -std=c11 -ffreestanding -nostdlib -nostdinc -fno-stack-protector -m32 -Iklibc/include -g -c -o $@ $<
$(CC) -DMEMMAP_BASE=$(MEMMAP_BASE) -std=c11 -ffreestanding -nostdlib -nostdinc -fno-stack-protector -m32 -Iklibc/include -g -c -o $@ $<
$(BUILD_DIR)/klibc/%.o: klibc/src/%.c
$(CC) -std=c11 -ffreestanding -nostdlib -nostdinc -fno-stack-protector -m32 -Iklibc/include -g -c -o $@ $<