memmem（）的分段错误

问题描述：

我正在尝试查找3D打印机的.gcode文件中某些图层的字节大小。但是，从运行函数来查找字符串“LAYER：*”的两个实例之间的距离时出现错误。这里是我的功能来源：memmem（）的分段错误

char* storeLayers(FILE* fp, int count) { 
    double size = get_filesize(fp); 
    uint8_t* file = (uint8_t*)malloc(size); 
    if(!file) { 
     printf("Error allocating 0x%lX bytes for GCode file\n",size); 
     fclose(fp); 
     return NULL; 
    } 
    int layerLen[] = {0}; 
    fread(file,1,size,fp); 
    char* layerstr = NULL; 
    char* layer = ";LAYER:"; 
    char layernum[100]; 
    char* pointerlayernum; 
    uint8_t* layerfind; 
    uint8_t* lastLayerfind = 0; 
    uint8_t* tmpfind; 
    for(int i = 0; i <= count; i++) { 
     sprintf(layernum,"%d",i); 
     pointerlayernum = layernum; 
     // make count string 
     layerstr = addVars(layer,pointerlayernum); 
     printf("|%s|\n",layerstr); 
     layerfind = memmem(file,size,layerstr,strlen(layerstr); 
     if(!layerfind) { 
      printf("Unable to find %s in the file\n",layerstr); 
      return NULL; 
     } 
     printf("Found \"%s\" at 0x%08lX\n",layerstr,layerfind - file); 
     if(lastLayerfind != 0) { 
      tmpfind = (uint8_t*)(layerfind - file); 
      layerLen[i] = tmpfind - lastLayerfind; 
      printf("Length of layer block: 0x%X bytes\n",layerLen[i]); 
     } 
     lastLayerfind = (uint8_t*)(layerfind - file); 
    } 
    return "blah"; 
}

的addVars（）函数如下：

char* addVars(char *s1, char *s2) { 
    char *result = malloc(strlen(s1)+strlen(s2)+1); 
    strcpy(result, s1); 
    strcat(result, s2); 
    return result; 
}

这个错误似乎只出现当我尝试在int count处理超过2层。这是正常的程序输出：

MacBook-Pro-27:fchost dayt0n$ ./fchost -d /Users/dayt0n/Downloads/paper_bin.gcode 
Layers: 509 
Filament Length: 4392.00 mm 
|;LAYER:0| 
Found ";LAYER:0" at 0x0000035F 
|;LAYER:1| 
Found ";LAYER:1" at 0x00002E67 
Length of layer block: 0x2B08 bytes 
|;LAYER:2| 
Segmentation fault: 11

我GDB坏了一些奇怪的原因，所以我用LLDB，这就是LLDB告诉我：

MacBook-Pro-27:fchost dayt0n$ lldb fchost 
(lldb) target create "fchost" 
Current executable set to 'fchost' (x86_64). 
(lldb) r -d /Users/dayt0n/Downloads/paper_bin.gcode /d 
Process 21523 launched: '/Users/dayt0n/Github/fchost/fchost' (x86_64) 
Layers: 509 
Filament Length: 4392.00 mm 
|;LAYER:0| 
Found ";LAYER:0" at 0x0000035F 
|;LAYER:1| 
Found ";LAYER:1" at 0x00002E67 
Length of layer block: 0x2B08 bytes 
|;LAYER:2| 
Process 21523 stopped 
* thread #1: tid = 0xf706b, 0x00007fffeaa8338b libsystem_c.dylib`memmem + 104, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=2, address=0x100093000) 
    frame #0: 0x00007fffeaa8338b libsystem_c.dylib`memmem + 104 
libsystem_c.dylib`memmem: 
-> 0x7fffeaa8338b <+104>: movzbl (%rbx), %eax 
    0x7fffeaa8338e <+107>: cmpl %r13d, %eax 
    0x7fffeaa83391 <+110>: jne 0x7fffeaa833a5   ; <+130> 
    0x7fffeaa83393 <+112>: movq %rbx, %rdi 
(lldb)

因此，根据LLDB，我知道问题似乎存在于访问memmem内。任何帮助将不胜感激。

那么当你用'lldb'单步执行代码时会发生什么？在我看来，这将是一种宝贵的学习技能。我，我会看着'int layerLen [] = {0};'，'for（int i = 0; i paxdiablo

啊！就是这样，谢谢！是的，我目前在另一个标签中打开了一个lldb指南。 – Dayt0n

你应该看看[适当的C格式]（// prohackr112.tk/r/properties-formatting）。或者学习如何[彻底模糊你的代码]（// prohackr112.tk/r/proper-c-obfuscation）。 –

答

I ' d看着int layerLen[] = {0};,for(int i = 0; i <= count; i++) {,layerLen[i] = tmpfind - lastLayerfind;序列。该定义仅允许一个int，这取决于count的值，这可能会导致问题。 – paxdiablo

memmem（）的分段错误

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