clang000-2019-03-21
2019-04-05 本文已影响0人
烽火扬州
1.1
#include <stdio.h>
int main() {
return 0;
}
(gdb) disas
Dump of assembler code for function main:
0x00000000004004d6 <+0>: push %rbp
0x00000000004004d7 <+1>: mov %rsp,%rbp 建立堆栈
0x00000000004004da <+4>: mov $0x0,%eax 返回值0
0x00000000004004df <+9>: pop %rbp
0x00000000004004e0 <+10>: retq
End of assembler dump.
1.2
#include <stdio.h>
int main() {
return 10;
}
Dump of assembler code for function main:
0x00000000004004d6 <+0>: push %rbp
0x00000000004004d7 <+1>: mov %rsp,%rbp
=> 0x00000000004004da <+4>: mov $0xa,%eax
0x00000000004004df <+9>: pop %rbp
0x00000000004004e0 <+10>: retq
End of assembler dump.
2.1
#include <stdio.h>
void fun1() {
}
int main() {
fun1();
return 10;
}
Dump of assembler code for function main:
0x00000000004004dd <+0>: push %rbp
0x00000000004004de <+1>: mov %rsp,%rbp
0x00000000004004e1 <+4>: mov $0x0,%eax
0x00000000004004e6 <+9>: callq 0x4004d6 <fun1>
=> 0x00000000004004eb <+14>: mov $0xa,%eax
0x00000000004004f0 <+19>: pop %rbp
0x00000000004004f1 <+20>: retq
End of assembler dump.
Dump of assembler code for function fun1:
0x00000000004004d6 <+0>: push %rbp
0x00000000004004d7 <+1>: mov %rsp,%rbp
=> 0x00000000004004da <+4>: nop
0x00000000004004db <+5>: pop %rbp
0x00000000004004dc <+6>: retq
End of assembler dump.
2.2
#include <stdio.h>
int fun1() {
return 16;
}
int main() {
fun1();
return 10;
}
Dump of assembler code for function fun1:
0x00000000004004d6 <+0>: push %rbp
0x00000000004004d7 <+1>: mov %rsp,%rbp
0x00000000004004da <+4>: mov $0x10,%eax
0x00000000004004df <+9>: pop %rbp
0x00000000004004e0 <+10>: retq
End of assembler dump.
Dump of assembler code for function main:
0x00000000004004e1 <+0>: push %rbp
0x00000000004004e2 <+1>: mov %rsp,%rbp
0x00000000004004e5 <+4>: mov $0x0,%eax
0x00000000004004ea <+9>: callq 0x4004d6 <fun1>
=> 0x00000000004004ef <+14>: mov $0xa,%eax
0x00000000004004f4 <+19>: pop %rbp
0x00000000004004f5 <+20>: retq
End of assembler dump.
2.3
#include <stdio.h>
int fun1(int m) {
return m;
}
int main() {
fun1(16);
return 10;
}
Dump of assembler code for function fun1:
0x00000000004004d6 <+0>: push %rbp
0x00000000004004d7 <+1>: mov %rsp,%rbp
0x00000000004004da <+4>: mov %edi,-0x4(%rbp)
0x00000000004004dd <+7>: mov -0x4(%rbp),%eax
0x00000000004004e0 <+10>: pop %rbp
0x00000000004004e1 <+11>: retq
End of assembler dump.
Dump of assembler code for function main:
0x00000000004004e2 <+0>: push %rbp
0x00000000004004e3 <+1>: mov %rsp,%rbp
0x00000000004004e6 <+4>: mov $0x10,%edi
0x00000000004004eb <+9>: callq 0x4004d6 <fun1>
=> 0x00000000004004f0 <+14>: mov $0xa,%eax
0x00000000004004f5 <+19>: pop %rbp
0x00000000004004f6 <+20>: retq
End of assembler dump.
2.4
#include <stdio.h>
int fun1(int m) {
return m;
}
int main() {
int a;
a = fun1(16);
return 10;
}
Dump of assembler code for function fun1:
0x00000000004004d6 <+0>: push %rbp
0x00000000004004d7 <+1>: mov %rsp,%rbp
0x00000000004004da <+4>: mov %edi,-0x4(%rbp)
=> 0x00000000004004dd <+7>: mov -0x4(%rbp),%eax
0x00000000004004e0 <+10>: pop %rbp
0x00000000004004e1 <+11>: retq
End of assembler dump.
Dump of assembler code for function main:
0x00000000004004e2 <+0>: push %rbp
0x00000000004004e3 <+1>: mov %rsp,%rbp
0x00000000004004e6 <+4>: sub $0x10,%rsp
0x00000000004004ea <+8>: mov $0x10,%edi
0x00000000004004ef <+13>: callq 0x4004d6 <fun1>
0x00000000004004f4 <+18>: mov %eax,-0x4(%rbp)
=> 0x00000000004004f7 <+21>: mov $0xa,%eax
0x00000000004004fc <+26>: leaveq
0x00000000004004fd <+27>: retq
End of assembler dump.
3.1
printf("*******%s,%s,%d*******\n",__FUNCTION__,__FILE__,__LINE__);
#include <stdio.h>
#define NUM 100
int main(){
#ifdef DEBUG
printf("*******%s,%s,%d*******\n",__FUNCTION__,__FILE__,__LINE__);
#endif
printf("Hello!\n");
return 0;
}
root@vultr:~/clang# ls
002.c
root@vultr:~/clang# gcc -DDEBUG -o 002 002.c
root@vultr:~/clang# ls
002 002.c
root@vultr:~/clang# ./002
*******main,002.c,5*******
Hello!
root@vultr:~/clang# rm 002
root@vultr:~/clang# ls
002.c
root@vultr:~/clang# gcc -o 002 002.c
root@vultr:~/clang# ls
002 002.c
root@vultr:~/clang# ./002
Hello!
root@vultr:~/clang# ^C
root@vultr:~/clang#
3.2
ANSI C一共只有32个关键字，9种控制语句，程序书写形式自由，区分大小写。把高级语言的基本结构和语句与低级语言的实用性结合起来。 C 语言可以像汇编语言一样对位、字节和地址进行操作，而这三者是计算机最基本的工作单元。
C语言的运算符包含的范围很广泛，共有34种运算符。C语言把括号、赋值、强制类型转换等都作为运算符处理。从而使C语言的运算类型极其丰富，表达式类型多样化。灵活使用各种运算符可以实现在其它高级语言中难以实现的运算。
关键字 sizeof,非函数！所以在任何环境下都可以使用。
关键字 return,函数返回。
char int short long unsigned signed float double void
struct union enum typedef,定义数据类型，圈地用的。
if 、else
switch、case、default
do 、while、for
continue、break、goto，逻辑结构，控制干活儿的顺序：顺序执行、分支执行、循环执行。
auto、register、static、const、extern、volatile，类型修饰符，（修饰数据类型，用来修饰上面那些个限制内存大小的数据类型），对内存资源存放位置的限定。
部分关键字解释：
break：跳出当前循环
continue：结束当前循环，开始下一轮循环
case：开关语句分支
default：开关语句中的“其它”分支
goto：无条件跳转语句
return ：子程序返回语句（可以带参数，也可不带参数）
register：声明寄存器变量
sizeof：计算数据类型或变量长度（即所占字节数）
volatile：说明变量在程序执行中可被隐含地改变
auto ：声明自动变量
extern：声明变量或函数是在其它文件或本文件的其他位置定义
Relevant Link:
c语言关键字总结 - 二郎三郎 - 博客园
算术操作运算：
+ - * / %
逻辑运算（返回结果0或1，假就是零，非零就是真）：
|| &&
> >= < <=
!
? :
位运算：
<< >>
| &
^ ~
赋值运算：
=
+= -= &= ...
内存访问符号：
()
[]
{}
-> .
& *
Relevant Link:
异或运算的性质及用途 - 氏名無 - CSDN博客
3.3
register关键字
//"register.c"
#include <stdio.h>
int main(){
register int a;
a=0x10;
printf("the a is %d\n",a);
return 0;
}
//"register2.c"
#include <stdio.h>
int main(){
int a;
a=0x10;
printf("the a is %d\n",a);
return 0;
}
root@vultr:~/clang# ls
register2.c register.c
root@vultr:~/clang# gcc -o register register.c
root@vultr:~/clang# gcc -o register2 register2.c
root@vultr:~/clang# ls
register register2 register2.c register.c
root@vultr:~/clang# ./register
the a is 16
root@vultr:~/clang# ./register2
the a is 16
root@vultr:~/clang# rm register register2
root@vultr:~/clang# ls
register2.c register.c
root@vultr:~/clang# gcc -c -o register register.c
root@vultr:~/clang# gcc -c -o register2 register2.c
root@vultr:~/clang# ls
register register2 register2.c register.c
root@vultr:~/clang# objdump -d register
register: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <main>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 53 push %rbx
5: 48 83 ec 08 sub $0x8,%rsp
9: bb 10 00 00 00 mov $0x10,%ebx
e: 89 de mov %ebx,%esi
10: bf 00 00 00 00 mov $0x0,%edi
15: b8 00 00 00 00 mov $0x0,%eax
1a: e8 00 00 00 00 callq 1f <main+0x1f>
1f: b8 00 00 00 00 mov $0x0,%eax
24: 48 83 c4 08 add $0x8,%rsp
28: 5b pop %rbx
29: 5d pop %rbp
2a: c3 retq
root@vultr:~/clang# objdump -d register2
register2: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <main>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 83 ec 10 sub $0x10,%rsp
8: c7 45 fc 10 00 00 00 movl $0x10,-0x4(%rbp)
f: 8b 45 fc mov -0x4(%rbp),%eax
12: 89 c6 mov %eax,%esi
14: bf 00 00 00 00 mov $0x0,%edi
19: b8 00 00 00 00 mov $0x0,%eax
1e: e8 00 00 00 00 callq 23 <main+0x23>
23: b8 00 00 00 00 mov $0x0,%eax
28: c9 leaveq
29: c3 retq
root@vultr:~/clang#
3.4
//"shiftr.c"
#include <stdio.h>
int main(){
int a=32;
while(a){
a=a>>1;
}
printf("**************\n");
}
root@vultr:~/clang# gcc -o shiftr shiftr.c
root@vultr:~/clang# ls
shiftr shiftr.c
root@vultr:~/clang# ./shiftr
**************
root@vultr:~/clang# gcc -c -o shiftr.o shiftr.c
root@vultr:~/clang# ls
shiftr shiftr.c shiftr.o
root@vultr:~/clang# objdump -d shiftr.o
shiftr.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <main>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 83 ec 10 sub $0x10,%rsp
8: c7 45 fc 20 00 00 00 movl $0x20,-0x4(%rbp)
f: eb 03 jmp 14 <main+0x14>
11: d1 7d fc sarl -0x4(%rbp)
14: 83 7d fc 00 cmpl $0x0,-0x4(%rbp)
18: 75 f7 jne 11 <main+0x11>
1a: bf 00 00 00 00 mov $0x0,%edi
1f: e8 00 00 00 00 callq 24 <main+0x24>
24: b8 00 00 00 00 mov $0x0,%eax
29: c9 leaveq
2a: c3 retq
root@vultr:~/clang#
修改为int a=-32;，会让程序陷入死循环。
root@vultr:~/clang# gcc -o shiftr shiftr.c
root@vultr:~/clang# ./shiftr
^C
root@vultr:~/clang# gcc -c -o shiftr.o shiftr.c
root@vultr:~/clang# ls
shiftr shiftr.c shiftr.o
root@vultr:~/clang# objdump -d shiftr.o
shiftr.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <main>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 83 ec 10 sub $0x10,%rsp
8: c7 45 fc e0 ff ff ff movl $0xffffffe0,-0x4(%rbp)
f: eb 03 jmp 14 <main+0x14>
11: d1 7d fc sarl -0x4(%rbp)
14: 83 7d fc 00 cmpl $0x0,-0x4(%rbp)
18: 75 f7 jne 11 <main+0x11>
1a: bf 00 00 00 00 mov $0x0,%edi
1f: e8 00 00 00 00 callq 24 <main+0x24>
24: b8 00 00 00 00 mov $0x0,%eax
29: c9 leaveq
2a: c3 retq
root@vultr:~/clang#
