Step1: build with busybox.

Signed-off-by: Chen Wang <wangchen20@iscas.ac.cn>

package/opensbi/hello.s

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+# hello.s - RISC-V 64 位裸机程序, 打印 "hello world!" 到控制台
+
+.section .text
+.global _start
+_start:
+    # 0x80000000 <- OpenSBI
+    # 0x80200000 <- hello.bin
+    # 0x80210000 <- 栈顶
+    
+    # 设置栈指针
+    li sp, 0x80210000
+    
+    # 调用打印函数
+    call print_hello
+    
+    # 无限循环（退出 qemu 需要按 Ctrl+A X）
+1:  j 1b
+
+# 打印 "hello world!" 函数
+print_hello:
+    # 保存返回地址
+    addi sp, sp, -8
+    sd ra, 0(sp)
+    
+    # 加载字符串地址
+    la a0, hello_string
+    
+    # 调用字符串打印函数
+    call puts
+    
+    # 恢复返回地址
+    ld ra, 0(sp)
+    addi sp, sp, 8
+    ret
+
+# 字符串打印函数 void puts(char *str)
+# a0: 字符串地址
+puts:
+    # 保存寄存器
+    addi sp, sp, -16
+    sd ra, 8(sp)
+    sd s0, 0(sp)
+    
+    mv s0, a0  # 保存字符串地址
+
+PRINT_LOOP:
+    # 读取一个字符
+    lb a0, 0(s0)
+    beq a0, zero, PRINT_DONE  # 直到遇到 '\0' 结束
+    
+    # 调用字符打印函数
+    call putc
+    
+    # 下一个字符
+    addi s0, s0, 1
+    j PRINT_LOOP
+
+PRINT_DONE:
+    # 恢复寄存器
+    ld s0, 0(sp)
+    ld ra, 8(sp)
+    addi sp, sp, 16
+    ret
+
+# 字符打印函数 void putc(char c)
+# a0: 要打印的字符
+putc:
+    # 使用 SBI 调用 (console_putchar)
+    li a7, 0x01  # SBI_EXT_0_1_CONSOLE_PUTCHAR
+    ecall
+    ret
+
+# 数据段
+.section .rodata
+hello_string:
+    .asciz "\nHello RISC-V world!\n"
+
+# 对齐到4字节边界
+.align 2

package/opensbi/hello.sh

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+#!/usr/bin/bash
+source $(dirname "$0")/../common.sh
+
+rm -f hello.o hello.elf hello.bin
+
+# 编译
+${CROSS_COMPILE}as hello.s -o hello.o
+${CROSS_COMPILE}ld hello.o -Ttext=0x80200000 -o hello.elf
+${CROSS_COMPILE}objcopy -O binary hello.elf hello.bin
+
+# 运行
+echo "Running in QEMU..."
+echo "Press Ctrl+A then X to exit"
+qemu-system-riscv64 \
+    -M virt \
+    -m 256M \
+    -nographic \
+    -bios ${IMAGES_DIR}/fw_jump.bin \
+    -kernel hello.bin

package/opensbi/make.sh

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+#!/usr/bin/bash
+source $(dirname "$0")/../common.sh
+
+PKGNAME=opensbi
+PKGVERSION=1.6
+PKGSOURCE_DIR=opensbi
+PKGSOURCE=opensbi-1.6.tar.gz
+PKGURL=https://github.com/riscv-software-src/opensbi/archive/v1.6/opensbi-1.6.tar.gz
+
+PKGBUILDNAME=${PKGNAME}
+PKGBUILD_DIR=${BUILD_DIR}/${PKGBUILDNAME}-${PKGVERSION}
+
+echo "----> Building ${PKGBUILDNAME} ..."
+
+stamp_downloaded
+
+step_start extract
+mkdir -p ${PKGBUILD_DIR}
+gzip -d -c ${DL_DIR}/${PKGSOURCE_DIR}/${PKGSOURCE} | tar --strip-components=1 -C ${PKGBUILD_DIR} -xf -
+chmod -R +rw ${PKGBUILD_DIR}
+step_end extract
+
+stamp_patched
+
+stamp_configured
+
+step_start build
+eval "${TARGET_MAKE_ENV} CROSS_COMPILE=${CROSS_COMPILE}  PLATFORM=generic /usr/bin/make -j${MAXNUM_CPUS} -C ${PKGBUILD_DIR}"
+step_end build
+
+step_start install-image
+/usr/bin/install -m 0644 -D ${PKGBUILD_DIR}/build/platform/generic/firmware/fw_jump.bin ${IMAGES_DIR}/fw_jump.bin
+step_end install-image
+
+stamp_installed
+
+echo "<---- ${PKGBUILDNAME} build complete."