[add] laos using xv6-riscv thought

laos/src/kernel/Makefile

@@ -0,0 +1,28 @@
+CURNAME		:= kernel
+BUILD_DIR	:= $(TOP_BUILD_DIR)/$(CURNAME)
+
+CSRC		:= $(wildcard *.c)
+OBJS		:= $(patsubst %.c,%.o,$(CSRC))
+BUILD_OBJS	:= $(addprefix $(BUILD_DIR)/,$(OBJS))
+
+ASSRC		:= $(wildcard *.S)
+ASOBJ		:= $(patsubst %.S,%.o,$(ASSRC))
+BUILD_ASOBJ	:= $(addprefix $(BUILD_DIR)/,$(ASOBJ))
+
+.PHONY: build all message
+
+all: message build
+
+$(BUILD_DIR):
+	@mkdir -p $(BUILD_DIR)
+
+$(BUILD_OBJS): $(BUILD_DIR)/%.o:%.c $(BUILD_DIR)
+	@$(CC) -c -o $@ $< $(CPPFLAGS) $(CFLAGS)
+
+$(BUILD_ASOBJ): $(BUILD_DIR)/%.o:%.S $(BUILD_DIR)
+	@$(CC) -c -o $@ $< $(CPPFLAGS) $(CFLAGS)
+
+build: $(BUILD_OBJS) $(BUILD_ASOBJ)
+
+message:
+	@echo "building $(CURNAME)"

laos/src/kernel/entry.S

@@ -0,0 +1,20 @@
+#include "asm.h"
+
+.section .entry
+.global _entry
+_entry:
+        # set up a stack for C.
+        # stack0 is declared in start.c,
+        # with a 4096-byte stack per CPU.
+        # sp = stack0 + (hartid * 4096)
+        la.global $sp, stack0
+        lu12i.w $a0, (1024*4 >> 12) & 0xfffff
+        addi.w $a0, $a0, 1024*4 & 0xfff
+        csrrd $a1, CPUID
+        addi.w $a1, $a1, 1
+        mul.w $a0, $a0, $a1
+        add.w $sp, $sp, $a0
+        # jump to start() in start.c
+        bl start
+spin:
+        b spin

laos/src/kernel/kalloc.c

@@ -0,0 +1 @@
+extern char end[];

laos/src/kernel/main.c

@@ -0,0 +1,3 @@
+void main() {
+
+}

laos/src/kernel/start.c

@@ -0,0 +1,7 @@
+#include "common.h"
+
+__attribute__ ((aligned (16))) char stack0[4096 * NCPU];
+
+void start() {
+
+}

laos/src/kernel/vm.c

@@ -0,0 +1 @@
+extern char etext[];