《Programming from the Ground Up》阅读笔记：p117-p146

news2024/11/18 7:24:53

《Programming from the Ground Up》学习第8天，p117-p146总结，总计30页。

一、技术总结

1.共享函数用法示例

(1)不使用共享函数

linux.s：

# filename:linux.s

# system call numbers(按数字大小排列，方便查看)
.equ SYS_READ, 0
.equ SYS_WRITE, 1
.equ SYS_OPEN, 2
.equ SYS_CLOSE, 3
.equ SYS_EXIT, 60

# standard file descriptors
.equ STDIN, 0
.equ STDOUT, 1
.equ STDERR, 2

# common status codes
.equ END_OF_FILE, 0

helloworld-nolib.s：

#filename: helloworld-nolib.s
# 编译命令：
 # as helloworld-nolib.s -o helloworld-nolib.o
 # ld helloworld-nolib.o -o helloworld-lib
.include "linux.s"

.section .data
helloworld:
	.ascii "hello world\n"
helloworld_end:
	#helloworld_end - helloworld的意思：
	.equ helloworld_len, helloworld_end - helloworld
.section .text
	.global _start

_start:
	#write涉及到SYS_WRITE，
	movq  $SYS_WRITE, %rax
    movq  $STDOUT, %rdi
    movq  $helloworld, %rsi
    movq  $helloworld_len, %rdx
    syscall
    
	# 退出函数: exit()
    movq  $SYS_EXIT, %rax
    movq  $0, %rdi
    syscall

执行helloworld-nolib结果：

# ./helloworld-nolib
hello world

(2)使用共享函数：print、exit

helloworld-lib.s:

# filename: helloworld-lib.s
# 编译命令：
 # as helloworld-lib.s -o helloworld-lib.o
 # ld -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o helloworld-lib helloworld-lib.o -lc
.section .data
helloworld:
    .ascii "hello world\n\0"

.section .text
    .globl _start
    
_start:
    movq $helloworld, %rdi
    call printf # C语言中的printf
    movq $0, %rdi
    call  exit # C语言中的exit

执行helloworld-lib结果：

# ./helloworld-nolib
hello world

2.问题：-bash: ./helloworld-lib: No such file or directory

问题描述

root@LAPTOP-5PGRQ2IO:/mnt/d/Projects/AssemblyProjects# ld -dynamic-linker /lib/ld-linux.so.2 -o helloworld-lib helloworld-lib.o -lc
root@LAPTOP-5PGRQ2IO:/mnt/d/Projects/AssemblyProjects# ll
total 96
drwxrwxrwx 1 root root  4096 Sep 28 15:48 ./
drwxrwxrwx 1 root root  4096 Jun 24 07:23 ../
-rwxrwxrwx 1 root root   147 Aug 25 16:18 add-year.s*
-rwxrwxrwx 1 root root  1075 Aug 31 18:55 count-chars.s*
-rwxrwxrwx 1 root root   112 Aug 25 16:26 error-exit.s*
-rwxrwxrwx 1 root root   863 Jul  1 23:39 exit.s*
-rwxrwxrwx 1 root root 14048 Sep 28 15:48 helloworld-lib*
-rwxrwxrwx 1 root root   920 Sep 28 15:47 helloworld-lib.o*
-rwxrwxrwx 1 root root   224 Sep  2 08:43 helloworld-lib.s*
-rwxrwxrwx 1 root root  9224 Sep 28 15:44 helloworld-nolib*
-rwxrwxrwx 1 root root  1208 Sep  2 08:39 helloworld-nolib.o*
-rwxrwxrwx 1 root root   510 Sep  2 08:39 helloworld-nolib.s*
-rwxrwxrwx 1 root root   264 Aug 24 17:52 linux.s*
-rwxrwxrwx 1 root root   774 Jul  3 06:25 maximum.s*
drwxrwxrwx 1 root root  4096 Aug 25 16:20 pgu_64-master/
-rwxrwxrwx 1 root root  2318 Jul 16 07:52 power.s*
-rwxrwxrwx 1 root root   453 Aug 24 18:14 read-record.s*
-rwxrwxrwx 1 root root  1333 Aug 24 18:15 read-records.s*
-rwxrwxrwx 1 root root   117 Aug 23 08:23 record-def.s*
-rwxrwxrwx 1 root root   984 Aug 24 17:58 test.dat*
-rwxrwxrwx 1 root root  5612 Jul 27 11:47 toupper.s*
-rwxrwxrwx 1 root root  1128 Aug 24 17:57 write-record.o*
-rwxrwxrwx 1 root root   686 Aug 24 17:54 write-record.s*
-rwxrwxrwx 1 root root 10816 Aug 24 17:58 write-records*
-rwxrwxrwx 1 root root  2632 Aug 24 17:57 write-records.o*
-rwxrwxrwx 1 root root  2081 Aug 24 17:57 write-records.s*
root@LAPTOP-5PGRQ2IO:/mnt/d/Projects/AssemblyProjects# ./helloworld-lib
-bash: ./helloworld-lib: No such file or directory

在执行 ./helloworld-lib 命令时提示 -bash: ./helloworld-lib: No such file or directory，但 helloworld-lib 实际上是存在的。

原因分析

/lib/ld-linux.so.2用于32位可执行文件，本人的系统是64位的WSL Ubuntu22.04，查看该文件是否存在：
```
# ls /lib/ld-linux.so.2
ls: cannot access '/lib/ld-linux.so.2': No such file or directory
```
执行 ls /lib/ld-linux.so.2 命令可以发现系统中没有 /lib/ld-linux.so.2 这个文件，所以虽然执行ld命令时没有报错，但是执行 ./helloworld-lib 命令时报错了：-bash: ./helloworld-lib: No such file or directory。
解决方法

因为电脑是 64 位的，所以使用 /lib64/ld-linux-x86-64.so.2 而不是 /lib/ld-linux.so.2：
```
ld -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o helloworld-lib helloworld-lib.o -lc
```