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Switch to a 64-bit version of the kernel and rt0 code
The switch to 64-bit mode allows us to use 48-bit addressing and to relocate the kernel to virtual address 0xffff800000000000 + 1M. The actual kernel is loaded by the bootloader at physical address 1M. The rt0 code has been split in two parts. The 32-bit part provides the entrypoint that the bootloader jumps to after loading the kernel. Its purpose is to make sure that: - the kernel was booted by a multiboot-compliant bootloader - the multiboot info structures are copied to a reserved memory block where they can be accessed after enabling paging - the CPU meets the minimum requirements for the kernel (CPUID, SSE, support for long-mode) Since paging is not enabled when the 32-bit code runs, it needs to translate all memory addresses it accesses to physical memory addresses by subtracting PAGE_OFFSET. The 32-bit rt0 code will set up a page table that identity-maps region: 0 to 8M and region: PAGE_OFFSET to PAGE_OFFSET+8M. This ensures that when paging gets enabled, we will still be able to access the kernel using both physical and virtual memory addresses. After enabling paging, the 32-bit rt0 will jump to a small 64-bit trampoline function that updates the stack pointer to use the proper virtual address and jumps to the virtual address of the 64-bit entry point. The 64-bit entrypoint sets up the minimal g0 structure required by the go function prologue for stack checks and sets up the FS register to point to it. The principle is the same as with 32-bit code (a segment register has the address of a pointer to the active g) with the difference that in 64-bit mode, the FS register is used instead of GS and that in order to set its value we need to write to a MSR.
This commit is contained in:
Achilleas Anagnostopoulos
45
Makefile
45
Makefile
@@ -1,5 +1,5 @@
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OS = $(shell uname -s)
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ARCH := x86
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ARCH := x86_64
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BUILD_DIR := build
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BUILD_ABS_DIR := $(CURDIR)/$(BUILD_DIR)
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@@ -13,10 +13,10 @@ LD := ld
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AS := nasm
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GOOS := linux
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GOARCH := 386
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GOARCH := amd64
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LD_FLAGS := -n -melf_i386 -T arch/$(ARCH)/script/linker.ld -static --no-ld-generated-unwind-info
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AS_FLAGS := -g -f elf32 -F dwarf -I arch/$(ARCH)/asm/
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LD_FLAGS := -n -T $(BUILD_DIR)/linker.ld -static --no-ld-generated-unwind-info
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AS_FLAGS := -g -f elf64 -F dwarf -I arch/$(ARCH)/asm/
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MIN_OBJCOPY_VERSION := 2.26.0
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HAVE_VALID_OBJCOPY := $(shell objcopy -V | head -1 | awk -F ' ' '{print "$(MIN_OBJCOPY_VERSION)\n" $$NF}' | sort -ct. -k1,1n -k2,2n && echo "y")
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@@ -28,7 +28,7 @@ asm_obj_files := $(patsubst arch/$(ARCH)/asm/%.s, $(BUILD_DIR)/arch/$(ARCH)/asm/
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kernel: binutils_version_check $(kernel_target)
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$(kernel_target): $(asm_obj_files) go.o
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$(kernel_target): $(asm_obj_files) linker_script go.o
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@echo "[$(LD)] linking kernel-$(ARCH).bin"
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@$(LD) $(LD_FLAGS) -o $(kernel_target) $(asm_obj_files) $(BUILD_DIR)/go.o
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@@ -36,14 +36,14 @@ go.o:
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@mkdir -p $(BUILD_DIR)
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@echo "[go] compiling go sources into a standalone .o file"
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@GOARCH=386 GOOS=linux go build -n 2>&1 | sed \
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@GOARCH=$(GOARCH) GOOS=$(GOOS) go build -n 2>&1 | sed \
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-e "1s|^|set -e\n|" \
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-e "1s|^|export GOOS=linux\n|" \
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-e "1s|^|export GOARCH=386\n|" \
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-e "1s|^|export GOOS=$(GOOS)\n|" \
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-e "1s|^|export GOARCH=$(GOARCH)\n|" \
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-e "1s|^|WORK='$(BUILD_ABS_DIR)'\n|" \
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-e "1s|^|alias pack='go tool pack'\n|" \
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-e "/^mv/d" \
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-e "s|-extld|-tmpdir='$(BUILD_ABS_DIR)' -linkmode=external -extldflags='-nostdlib' -extld|g" \
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-e "s|-extld|-tmpdir='$(BUILD_ABS_DIR)' -linkmode=external -extldflags='-nostartfiles -nodefaultlibs -nostdlib -r' -extld|g" \
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| sh 2>&1 | sed -e "s/^/ | /g"
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@# build/go.o is a elf32 object file but all go symbols are unexported. Our
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@@ -59,6 +59,13 @@ binutils_version_check:
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@echo "[binutils] checking that installed objcopy version is >= $(MIN_OBJCOPY_VERSION)"
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@if [ "$(HAVE_VALID_OBJCOPY)" != "y" ]; then echo "[binutils] error: a more up to date binutils installation is required" ; exit 1 ; fi
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linker_script:
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@echo "[sed] extracting LMA and VMA from constants.inc"
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@echo "[gcc] pre-processing arch/$(ARCH)/script/linker.ld.in"
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@gcc `cat arch/$(ARCH)/asm/constants.inc | sed -e "/^$$/d; /^;/d; s/^/-D/g; s/\s*equ\s*/=/g;" | tr '\n' ' '` \
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-E -x \
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c arch/$(ARCH)/script/linker.ld.in | grep -v "^#" > $(BUILD_DIR)/linker.ld
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$(BUILD_DIR)/arch/$(ARCH)/asm/%.o: arch/$(ARCH)/asm/%.s
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@mkdir -p $(shell dirname $@)
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@echo "[$(AS)] $<"
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@@ -87,22 +94,20 @@ iso:
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vagrant ssh -c 'cd $(VAGRANT_SRC_FOLDER); make iso'
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run: iso
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qemu-system-i386 -cdrom $(iso_target)
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qemu-system-$(ARCH) -cdrom $(iso_target)
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gdb: iso
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qemu-system-i386 -s -S -cdrom $(iso_target) &
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qemu-system-$(ARCH) -M accel=tcg -s -S -cdrom $(iso_target) &
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sleep 1
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gdb \
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-ex "add-auto-load-safe-path $(pwd)" \
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-ex "file $(kernel_target)" \
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-ex "set disassembly-flavor intel" \
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-ex 'set arch i386:intel' \
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-ex 'target remote localhost:1234' \
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-ex 'add-auto-load-safe-path $(pwd)' \
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-ex 'set disassembly-flavor intel' \
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-ex 'layout asm' \
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-ex 'b _rt0_entry' \
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-ex 'continue' \
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-ex 'disass'
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@killall qemu-system-i386 || true
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-ex 'set arch i386:intel' \
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-ex 'file $(kernel_target)' \
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-ex 'target remote localhost:1234' \
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-ex 'set arch i386:x86-64:intel'
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@killall qemu-system-$(ARCH) || true
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endif
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clean:
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