~~~~~C语言代码example.c

int triangle( int width, int height)

{

int arr{0,1,2,3,4};

int area;

area = width * height /2;

return (area);

}

void main()

{

triangle(5,4);

}

~~~~~gdb反汇编代码

$ gdb example

(gdb) disass main

Dump of assembler code for function main:

0x080483f6 :    push   %ebp

0x080483f7 :    mov    %esp,%ebp

0x080483f9 :    sub    $0x8,%esp

0x080483fc :    movl   $0x4,0x4(%esp)

0x08048404 :    movl   $0x5,(%esp)

0x0804840b :    call   0x80483b4 0x08048410 :    leave

0x08048411 :    ret

End of assembler dump.

(gdb) disass triangle

Dump of assembler code for function triangle:

0x080483b4 :    push   %ebp

0x080483b5 :    mov    %esp,%ebp

0x080483b7 :    sub    $0x20,%esp

0x080483ba :    movl   $0x0,-0x18(%ebp)

0x080483c1 :    movl   $0x1,-0x14(%ebp)

0x080483c8 :    movl   $0x2,-0x10(%ebp)

0x080483cf :    movl   $0x3,-0xc(%ebp)

0x080483d6 :    movl   $0x4,-0x8(%ebp)

0x080483dd :    mov    0x8(%ebp),%eax

0x080483e0 :    imul   0xc(%ebp),%eax

0x080483e4 :    mov    %eax,%edx

0x080483e6 :    shr    $0x1f,%edx

0x080483e9 :    lea    (%edx,%eax,1),%eax

0x080483ec :    sar    %eax

0x080483ee :    mov    %eax,-0x4(%ebp)

0x080483f1 :    mov    -0x4(%ebp),%eax

0x080483f4 :    leave

0x080483f5 :    ret

End of assembler dump.

~~~~~栈使用情况

~~~~~部分汇编代码解释

main:

mov %esp,%ebp ;esp-->ebp

sub $0x8,%esp ;esp-8-->esp

movl $0x4,0x4(%esp) ;4-->esp+4

movl $0x5,(%esp) ;5-->esp

call 0x80483b4 ;跳转到0x80483b4，同时将下一条指令的地址(0x08048410)压栈(即ret)

triangle:

sub $0x20,%esp ;esp-20-->esp

movl $0x0,-0x18(%ebp) ;0-->ebp-18

movl $0x1,-0x14(%ebp) ;1-->ebp-14

movl $0x2,-0x10(%ebp) ;2-->ebp-10

movl $0x3,-0xc(%ebp) ;3-->ebp-c

movl $0x4,-0x8(%ebp) ;4-->ebp-8

mov 0x8(%ebp),%eax ;ebp+8(即param1:5)-->eax

imul 0xc(%ebp),%eax ;ebp+c(即param2:4)*eax(即param1:5)

mov %eax,%edx

shr $0x1f,%edx ;逻辑右移(高位补0)

lea (%edx,%eax,1),%eax

sar %eax ;算术右移

mov %eax,-0x4(%ebp) ;把运算结果放入area变量中

mov -0x4(%ebp),%eax

leave

ret

enter等价于push %ebp

mov %esp,%ebp

leave等价于mov %ebp,%esp

pop %ebp

ret num等价于pop %eip

add num,%esp

movl variable,%eax ;把variable作为一个地址，取地址为variable处的值赋给eax

movl $variable,%eax ;把variable作为一个立即数赋给eax