RVOS练习4-1

RVOS

编写一个简单的打印 “hello world！” 的程序源文件：hello.c

1
2
3
4
5
6
#include <stdio.h>

void main()
{
  printf("hello world!");
}

对源文件进行编译，生成针对支持 rv32ima 指令集架构处理器的目标文件 hello.o

使用指令riscv64-unknown-elf-gcc -march=rv32ima -mabi=ilp32 -c hello.c进行编译出现以下错误

1
2
3
4
hello.c:1:10: fatal error: stdio.h: No such file or directory
    1 | #include <stdio.h>
      |          ^~~~~~~~~
compilation terminated.

该错误在errata.pdf中和gitee的issue有提及，根据errata.pdf，将gcc更换为riscv64-linux-gnu-gcc，使用指令riscv64-linux-gnu-gcc -march=rv32ima -mabi=ilp32 -c hello.c进行编译，仍出现报错，报错为

1
2
3
4
5
6
7
8
In file included from /usr/riscv64-linux-gnu/include/features.h:510,
                 from /usr/riscv64-linux-gnu/include/bits/libc-header-start.h:33,
                 from /usr/riscv64-linux-gnu/include/stdio.h:27,
                 from hello.c:1:
/usr/riscv64-linux-gnu/include/gnu/stubs.h:8:11: fatal error: gnu/stubs-ilp32.h: No such file or directory
    8 | # include <gnu/stubs-ilp32.h>
      |           ^~~~~~~~~~~~~~~~~~~
compilation terminated.

之后再issue下的讨论找到方法，只需要去除-march和-mabi选项即可.

查看 hello.o 的文件的文件头信息

使用指令readelf -h hello.o查看文件头信息，输出如下

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              REL (Relocatable file)
  Machine:                           RISC-V
  Version:                           0x1
  Entry point address:               0x0
  Start of program headers:          0 (bytes into file)
  Start of section headers:          840 (bytes into file)
  Flags:                             0x5, RVC, double-float ABI
  Size of this header:               64 (bytes)
  Size of program headers:           0 (bytes)
  Number of program headers:         0
  Size of section headers:           64 (bytes)
  Number of section headers:         12
  Section header string table index: 11

查看 hello.o 的 Section header table

使用指令readelf -SW hello.o查看Section header table，输出如下

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
There are 12 section headers, starting at offset 0x348:

Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000 000000 00      0   0  0
  [ 1] .text             PROGBITS        0000000000000000 000040 000022 00  AX  0   0  2
  [ 2] .rela.text        RELA            0000000000000000 000250 000090 18   I  9   1  8
  [ 3] .data             PROGBITS        0000000000000000 000062 000000 00  WA  0   0  1
  [ 4] .bss              NOBITS          0000000000000000 000062 000000 00  WA  0   0  1
  [ 5] .rodata           PROGBITS        0000000000000000 000068 00000d 00   A  0   0  8
  [ 6] .comment          PROGBITS        0000000000000000 000075 00002c 01  MS  0   0  1
  [ 7] .note.GNU-stack   PROGBITS        0000000000000000 0000a1 000000 00      0   0  1
  [ 8] .riscv.attributes RISCV_ATTRIBUTES 0000000000000000 0000a1 000033 00      0   0  1
  [ 9] .symtab           SYMTAB          0000000000000000 0000d8 000150 18     10  12  8
  [10] .strtab           STRTAB          0000000000000000 000228 000022 00      0   0  1
  [11] .shstrtab         STRTAB          0000000000000000 0002e0 000064 00      0   0  1

对 hello.o 反汇编，并查看 hello.c 的 C 程序源码和机器指令的对应关系

使用riscv64-linux-gnu-objdump -S hello.o查看反汇编后的代码，输出如下

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
hello.o:     file format elf64-littleriscv


Disassembly of section .text:

0000000000000000 <main>:
#include <stdio.h>

void main()
{
   0:   1141                    addi    sp,sp,-16
   2:   e406                    sd      ra,8(sp)
   4:   e022                    sd      s0,0(sp)
   6:   0800                    addi    s0,sp,16
  printf("hello world!");
   8:   00000517                auipc   a0,0x0
   c:   00050513                mv      a0,a0
  10:   00000097                auipc   ra,0x0
  14:   000080e7                jalr    ra # 10 <main+0x10>
}
  18:   0001                    nop
  1a:   60a2                    ld      ra,8(sp)
  1c:   6402                    ld      s0,0(sp)
  1e:   0141                    addi    sp,sp,16
  20:   8082                    ret