Valgrind: Conditional jump or move depends on uninitialised value(s)

**futuran** · 01-26-2019

Hi

When I check my c code with valgrind --track-origins=yes I get this error.

Code:

==4649== Conditional jump or move depends on uninitialised value(s)
==4649==    at 0x4C37928: strcspn (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4649==    by 0x4EDAB94: strtok_r (strtok_r.c:64)
==4649==    by 0x108D36: readDirectory (ps.c:132)
==4649==    by 0x108A9F: main (ps.c:37)
==4649==  Uninitialised value was created by a stack allocation
==4649==    at 0x108ACF: readDirectory (ps.c:52)
==4649== 
==4649== Conditional jump or move depends on uninitialised value(s)
==4649==    at 0x4EDAB9B: strtok_r (strtok_r.c:65)
==4649==    by 0x108D36: readDirectory (ps.c:132)
==4649==    by 0x108A9F: main (ps.c:37)
==4649==  Uninitialised value was created by a stack allocation
==4649==    at 0x108ACF: readDirectory (ps.c:52)
==4649== 
==4649== Conditional jump or move depends on uninitialised value(s)
==4649==    at 0x4C32D08: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4649==    by 0x4E994D2: vfprintf (vfprintf.c:1643)
==4649==    by 0x4EA0F25: printf (printf.c:33)
==4649==    by 0x108DDF: printOutput (ps.c:148)
==4649==    by 0x108D5F: readDirectory (ps.c:134)
==4649==    by 0x108A9F: main (ps.c:37)
==4649==  Uninitialised value was created by a stack allocation
==4649==    at 0x108ACF: readDirectory (ps.c:52)

This is a snippet from my Code.

Code:

void readDirectory(char pid[]){

  char path[50];
  char buffer[128];

  char name[128];
  static char *nameOutput;
  char *saveName = name;

  char vmrss[128];
  static char *vmrssOutput;
  char *saveVmrss = vmrss;

  while(fgets(buffer, sizeof(buffer), fptr)){
            if(strstr(buffer, "Name:")){

              strcpy(name, buffer);
              nameOutput = strtok_r(name, ":", &saveName);
              nameOutput = strtok_r(NULL, ":", &saveName);
 


              for(unsigned int i = strcspn (nameOutput, "\n"); i < strlen(nameOutput); i++){
                nameOutput[i] = 0;
              }

            } else if(strstr(buffer, "Uid:") && strstr(buffer, sUserID)){
                isUse = true;


                }else if(strstr(buffer, "VmRSS:")){
                      strncpy(vmrss, buffer, strlen(buffer) - 3);
                      vmrssOutput = strtok_r(vmrss, ":", &saveVmrss);
                      vmrssOutput = strtok_r(NULL, ":", &saveVmrss);

                      printOutput(isUse, pid, nameOutput, vmrssOutput);
                    }

I think the problem is, that i didn't initialized the variable char *saveVmrss = vmrss;
How can I solve this?

**laserlight** · 01-26-2019

For starters, you need to format your code better, e.g.,

Code:

void readDirectory(char pid[]) {
    char path[50];
    char buffer[128];

    char name[128];
    static char *nameOutput;
    char *saveName = name;

    char vmrss[128];
    static char *vmrssOutput;
    char *saveVmrss = vmrss;

    while (fgets(buffer, sizeof(buffer), fptr)) {
        if (strstr(buffer, "Name:")) {
            strcpy(name, buffer);
            nameOutput = strtok_r(name, ":", &saveName);
            nameOutput = strtok_r(NULL, ":", &saveName);

            for (unsigned int i = strcspn(nameOutput, "\n"); i < strlen(nameOutput); i++) {
                nameOutput[i] = 0;
            }
        } else if (strstr(buffer, "Uid:") && strstr(buffer, sUserID)) {
            isUse = true;
        } else if (strstr(buffer, "VmRSS:")) {
            strncpy(vmrss, buffer, strlen(buffer) - 3);
            vmrssOutput = strtok_r(vmrss, ":", &saveVmrss);
            vmrssOutput = strtok_r(NULL, ":", &saveVmrss);

            printOutput(isUse, pid, nameOutput, vmrssOutput);
        }

I note that you seem to have cut off the code before the end of the function, so it is hard to make recommendations as it is not known what comes next in the function.

Anyway, it looks like your use of the strtok_r state pointers is wrong. You should have written:

Code:

char name[128];
char *nameOutput;
char *saveName;

char vmrss[128];
char *vmrssOutput;
char *saveVmrss;

I removed the use of static because there is no evidence that you need static local variables here: what nameOutput points to will not be overwritten just because it is not static; it will be overwritten because the content of name is overwritten, as nameOutput will point to somewhere in name due to the strtok_r call.

You don't need that for loop with the strcspn call: you can just use the result of strcspn to overwrite the character at that index with a null character. Also, use '\0', not 0, for null characters.

**Salem** · 01-26-2019

> strncpy(vmrss, buffer, strlen(buffer) - 3);
Another issue might be that strncpy does not automatically append a \0 on the end of whatever it copies.

**futuran** · 01-27-2019

Originally Posted by Salem

> strncpy(vmrss, buffer, strlen(buffer) - 3);
Another issue might be that strncpy does not automatically append a \0 on the end of whatever it copies.

Thank you very much. You were rigth, the problem was the strncpy(vmrss, buffer, strlen(buffer) - 3).

When I didn't define char*nameOutput as static, the gcc throws a warning. Therefore I define it as static.
Now I haven't any errors from gcc and valgrind.

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