Kernel runs in the higher address space

kboot/Makefile

@@ -0,0 +1,27 @@
+DEST=$(O)/kboot
+OBJS=$(DEST)/main.o $(DEST)/data.o
+CFLAGS=-mno-sse -mno-mmx -mno-sse2 -mno-3dnow
+
+$(if $(O),,$(error Specify the target directory))
+
+$(DEST)/kboot.elf: $(DEST) $(DEST)/kernel.lds $(OBJS)
+	@$(LD) $(LDFLAGS) -o $@ -T $(DEST)/kernel.lds -nostdlib $(OBJS)
+
+$(DEST)/%.o: %.c
+	@$(CC) $(CFLAGS) -c -o $@ -O3 $<
+
+$(DEST)/data.o: data.S
+	@$(CC) -c -o $@ -O3 -DKIMAGE='"$(KIMAGE)"' $^
+
+$(DEST)/kernel.lds: kernel.lds.S
+	$(if $(LOAD_PA),,$(error Specify the loading physical address))
+	@$(CC) -E -P -DLOAD_PA=$(LOAD_PA) -o $@ $<
+
+$(DEST):
+	@mkdir -p $(DEST)
+
+clean:
+	@$(RM) $(DEST)/*
+
+.PHONY: clean
+

kboot/data.S

@@ -0,0 +1,9 @@
+#ifndef KIMAGE
+#error "No kernel image is specified"
+#endif
+
+.data
+.globl data_start
+data_start:
+.incbin KIMAGE
+

kboot/kernel.lds.S

@@ -0,0 +1,34 @@
+ENTRY(main)
+PHDRS 
+{
+	text PT_LOAD FLAGS(5);
+    data PT_LOAD FLAGS(7);
+}
+SECTIONS
+{
+	. = LOAD_PA;
+    _head = .;
+
+    .text : {
+        *(.text);
+    } : text
+
+    . = ALIGN(4096);
+	.data : {
+	      *(.data)
+	      *(.data.*)
+	} :data
+	.rodata : {
+	      *(.rodata .rodata.*)
+	} :data
+    .bss : {
+          *(.bss .bss.*)
+    }
+    . = ALIGN(4096);
+    data_end = .;
+
+	/DISCARD/ : {
+	     *(.eh_frame)
+         *(.note.gnu.build-id)
+	}
+}

kboot/main.c

@@ -0,0 +1,132 @@
+#include <elf.h>
+
+extern char data_start[], data_end[];
+
+#define LARGE_PAGE_SIZE  (1UL << 21)
+#define LARGE_PAGE_MASK  (~((unsigned long)LARGE_PAGE_SIZE - 1))
+
+#define MAP_ST_START       0xffff800000000000UL
+#define MAP_KERNEL_START   0xffffffff80000000UL
+
+#define PTL4_SHIFT         39
+#define PTL3_SHIFT         30
+#define PTL2_SHIFT         21
+
+unsigned long page_tables[3][512] __attribute__((aligned(4096)));
+
+static void *memcpy(void *dest, void *src, unsigned long len)
+{
+	char *d = dest, *s = src;
+
+	for ( ; len ; len--) {
+		*(d++) = *(s++);
+	}
+
+	return d;
+}
+static void *memset(void *dest, int v, unsigned long len)
+{
+	char *d = dest;
+
+	for ( ; len ; len--) {
+		*(d++) = (char)v;
+	}
+
+	return d;
+}
+
+void memzerol(unsigned long *p, unsigned long size)
+{
+	unsigned long i;
+
+	size /= sizeof(unsigned long);
+
+	for (i = 0; i < size; i++) {
+		p[i] = 0;
+	}
+}
+
+static unsigned long load_programs(unsigned char *image, Elf64_Phdr *hdrs,
+                                   int nhdr, unsigned long offset)
+{
+	int i;
+	unsigned long end = MAP_KERNEL_START;
+
+	for (i = 0; i < nhdr; i++) {
+		if (hdrs[i].p_type == PT_LOAD) {
+			memcpy((void *)(hdrs[i].p_vaddr - offset),
+			       image + hdrs[i].p_offset,
+			       hdrs[i].p_filesz);
+			if (hdrs[i].p_filesz < hdrs[i].p_memsz) {
+				memset((void *)(hdrs[i].p_vaddr + 
+				                hdrs[i].p_filesz - offset), 0,
+				       hdrs[i].p_memsz - hdrs[i].p_filesz);
+			}
+			if (end < hdrs[i].p_vaddr + hdrs[i].p_memsz) {
+				end = hdrs[i].p_vaddr + hdrs[i].p_memsz;
+			}
+		}
+	}
+
+	return end;
+}
+
+/*
+ * Return value: If success, the entry point address. Otherwise, 0.
+ */
+unsigned long load_elf(unsigned char *image, unsigned long offset)
+{
+	Elf64_Ehdr *hdr = (Elf64_Ehdr *)image;
+
+	if (hdr->e_ident[0] != 0x7f || hdr->e_ident[1] != 'E'
+	    || hdr->e_ident[2] != 'L' || hdr->e_ident[3] != 'F') {
+		return 0;
+	}
+	/* TODO: We may overlap. So copying should be more sophisticated */
+	if (!hdr->e_phoff || hdr->e_phentsize != sizeof(Elf64_Phdr)) {
+		return 0;
+	}
+	return load_programs(image,
+	                     (Elf64_Phdr *)(image + hdr->e_phoff), hdr->e_phnum,
+	                     offset);
+}
+
+void main(unsigned long param)
+{
+	/* Assume phys == virt */
+	unsigned long load_address, end, *org_cr3;
+	unsigned long i, n;
+	Elf64_Ehdr *hdr;
+	void (*entry)(unsigned long param, unsigned long load_address);
+
+	load_address = (unsigned long)data_end;
+	load_address = (load_address + LARGE_PAGE_SIZE - 1) & LARGE_PAGE_MASK;
+
+	asm volatile("movq %%cr3, %0" : "=r"(org_cr3));
+
+	memzerol((unsigned long *)page_tables, sizeof(page_tables));
+
+	page_tables[0][0] = org_cr3[0];
+	page_tables[0][(MAP_ST_START >> PTL4_SHIFT) & 511] = org_cr3[0];
+	page_tables[0][(MAP_KERNEL_START >> PTL4_SHIFT) & 511] = 
+		((unsigned long)page_tables[1]) | 3;
+	page_tables[1][(MAP_KERNEL_START >> PTL3_SHIFT) & 511] = 
+		((unsigned long)page_tables[2]) | 3;
+
+	end = load_elf(data_start, MAP_KERNEL_START - load_address);
+
+	/* map 4MB more in case */
+	n = (end - MAP_KERNEL_START + (1 << PTL2_SHIFT) - 1) >> PTL2_SHIFT;
+	n += 2;
+
+	for (i = 0; i < n; i++) {
+		page_tables[2][i] = (load_address + (i << PTL2_SHIFT)) | 0x83;
+	}
+
+	hdr = (Elf64_Ehdr *)data_start;
+
+	asm volatile("movq %0, %%cr3" : : "r"(page_tables) : "memory");
+	
+	entry = (void *)hdr->e_entry;
+	entry(param, load_address);
+}