ASM AT＆amp; T公司的语法 [英] ASM at&t syntax

问题描述

所以，我的问题，此code。这是一个程序，从二进制转换为数字deximal

so i've a problem with this code. This is a program for converting from binary to deximal numbers.

#include <cstdlib>
#include <iostream>
#include <cstdio>

char s[100];
    int length;
    int a;


int main(int argc, char *argv[])
{

    system("cls");
    printf("\n\n  Vvedite stroky iz 0 i 1 (do 8 delementov) > ");
    gets(s);

    asm("leal s,%esi");
    asm("movl 8,%ecx");
    asm("movl 0,%edx");
    asm("repeat:");
    asm("movl 1,%eax");
    asm("dec %ecx");
    asm("rol %cl,%eax");
    asm("cmpb 31,%esi");
    asm("jnz x");
    asm("add %eax,%edx");
    asm("x: inc %esi");
    asm("cmpb 0,$esi");
    asm("jnz repeat");
    asm("movl %edx,a");

    printf("4islo %d",a);

    return EXIT_SUCCESS;
}

它给了我：
分段故障（核心转储）

It gives me: "Segmentation fault (core dumped)"

请与本ASM部分提供帮助。
我认为这个问题在CMPB运营商。

Please help with this ASM part. I think the problem in the CMPB operator.

推荐答案

有一些问题与code - 我的系统上，它甚至没有通过编译/汇编运行。主要的问题是，你需要preFIX与 $ 所有文字，否则汇编器总是假设一个内存访问：

There are some issues with that code - on my system, it did not even run through the compiler/assembler. The main issue is that you need to prefix all literals with $, otherwise the assembler assumes a memory access:

asm("movl 8,%ecx"); // tries to access memory at address 8 => Segmentation fault

这必须是

asm("movl $8,%ecx"); // Moves literal 8 into ecx

相应调整所有其他指令。

Adjust all other instructions accordingly.

另一个问题是，下面的指令：

Another issue is the following instruction:

asm("cmpb 0,$esi");   // $esi is not a literal nor a register name

这必须是

asm("cmpb $0,(%esi)");  // compare value at address stored in %esi with literal 0 (end of string)

我建议你编译code调试信息，像

I suggest that you compile the code with debug information, like

$ g++ -g -o sample sample.c

有那么很容易调试程序：

It is then quite easy to debug the program:

$ gdb sample 
(gdb) run
Starting program: sample 
sh: cls: command not found

   Vvedite stroky iz 0 i 1 (do 8 delementov) > 10101010

Program received signal SIGSEGV, Segmentation fault.
main (argc=1, argv=0x7fffffffe238) at sample.c:18
18          asm("movl 8,%ecx");   // current bit position

正如你可以看到，调试器显示您这引起了分段故障的指令。

As you can see, the debugger shows you the instruction which caused the segmentation fault.

更新

组装code。通过@Brett的建议这为我工作，使用单个 ASM 语句：

The assembly code which worked for me, using a single asm statement as suggested by @Brett:

asm("leal s, %esi         \n\t"   // s => %esi
    "movl $8, %ecx        \n\t"   // current bit position (+1)
    "movl $0, %edx        \n"     // initialize result

"repeat:                  \n\t"
    "movl $1, %eax        \n\t"   // Create bit mask in %eax
    "dec  %ecx            \n\t"   // Decrement rotation counter to shift mask bit to proper position
    "rol  %cl, %eax       \n\t"   // calculate value of current binary digit

    "cmpb $0x31, (%esi)   \n\t"   // current digit == 1?
    "jnz  x               \n\t"   // no, skip
    "add  %eax, %edx      \n"     // add current value to %edx

 "x:                      \n\t"
    "inc  %esi            \n\t"   // next address in input string
    "cmpb $0, (%esi)      \n\t"   // end of string reached?
    "jnz  repeat          \n\t"   // no, continue

    "movl %edx,a          \n");   // store result in a variable

$ ./sample 

  Vvedite stroky iz 0 i 1 (do 8 delementov) > 10101010
4islo 170

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