How to solve segmentation fault in change main function inputs with C code?-CodePudding

I want the following code, which is related to the Sysbench tool (https://github.com/akopytov/sysbench), to change from the following code to the next code, but I get an error with just this small change (Segmentation fault (core dumped)).

./sysbench cpu --cpu-max-prime=2000 run

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

int main(void)
{  
 char *argv[]= {"./sysbench","cpu","--cpu-max-prime=2000","run", NULL};
 int argc = sizeof(argv) / sizeof(char*) - 1; 
           .
           .
           .

}

with GDB Debug :

Program received signal SIGSEGV, Segmentation fault.
0x000000000040aec8 in parse_option (
   name=name@entry=0x4768e8 "cpu-max-prime=2000", 
   ignore_unknown=ignore_unknown@entry=false) at sysbench.c:500
500     *tmp = '\0';

static int parse_option(char *name, bool ignore_unknown)
{
 const char        *value;
 char              *tmp;
 option_t          *opt;
 char              ctmp = 0;
 int               rc;

 tmp = strchr(name, '=');
 printf( "tmp: %s\n", tmp );
 if (tmp != NULL)
 {
   ctmp = *tmp;
   *tmp = '\0';
   value = tmp   1;
 }
 else
 {
   value = NULL;
 }

 opt = sb_find_option(name);
 if (opt != NULL || ignore_unknown)
   rc = set_option(name, value,
                   opt != NULL ? opt->type : SB_ARG_TYPE_STRING) == NULL;
 else
   rc =  1;

 if (tmp != NULL)
   *tmp = ctmp;

 return rc;
}

please help me. thanks.

CodePudding user response：

In order to emulate argv from main the strings pointed to by argv[n] to must be writable, which is not the case in your code where argv[n] point to string literals which cannot be written to.

Writing into a string literal is formally undefined behaviour in C, but on modern desktop platforms it typically triggers a seg fault.

And *tmp = '\0'; is actually writing into a string.

This should do the job, although I'm not entirely sure because I can't check it here easily.

int main(void)
{
  char arg1[] = "./sysbench";
  char arg2[] = "cpu";
  char arg3[] = "--cpu-max-prime=2000";
  char arg4[] = "run";
  char* argv[] = {arg1, arg2, arg3, arg4, NULL};
  ...
  
}