c - 哈希表 "Uninitialised value was created by a stack allocation"

Question

我们正在尝试建立一个哈希表和一些用于设置、获取和删除表中值的过程。我们在第 35 行和第 53 行遇到“条件跳转或移动取决于未初始化的值”问题。

==23720== Conditional jump or move depends on uninitialised value(s)
==23720==    at 0x400CF6: hash (hashserver.c:35)
==23720==    by 0x400D49: set (hashserver.c:53)
==23720==  Uninitialised value was created by a stack allocation
==23720==    at 0x40112A: main (hashserver.c:133)

为了防止哈希表中发生冲突，我们将使用链表进行单独链接。你能帮忙吗？谢谢!

typedef struct KeyVal {
    unsigned char* value;
    unsigned char* key;
    struct KeyVal* next;
}KeyVal;

unsigned long hash (unsigned char *str)
{
  unsigned long hash = 5381;
  int c;

  (line 35) -> while (c = *str++)
    hash = ((hash << 5) + hash) + c;    /* hash * 33 + c */

  return hash%MAXHASHTABLEN;
}

int set(KeyVal *hashtable[], unsigned char* key, unsigned char* value){
 (line 53)->   unsigned long hval = hash(key);

    if(hashtable[hval] == NULL){
        KeyVal* runvar = calloc(1, sizeof(KeyVal));
        runvar->key = key;
        runvar->value = value;
        runvar->next = NULL;
        hashtable[hval] = runvar;
        fprintf(stdout, "Successful set 1\n");
        return 1;
    } else {
    KeyVal* counter = hashtable[hval];
    KeyVal* prev = counter;
    while(counter!= NULL){
        prev = counter;
        counter = counter->next;
    }
        KeyVal* runvar = calloc(1, sizeof(KeyVal));
        runvar->key = key;
        runvar->value = value;
        runvar->next = NULL;
        prev->next = runvar;
        fprintf(stdout, "Successful set 2\n");
        return 2;
    }
    return -1;
}

(line 133) -> int main(int argc, char *argv[]){
    int sock, new, status, command;
    struct addrinfo hints, *serverinfo, *p; 
    struct sockaddr_storage their_addr; 
    socklen_t sin_size;
    int yes = 1;
    char s[INET6_ADDRSTRLEN]; 
    unsigned int numbytes = 0;
    char buffer[128];
    int line, transid, bitcounter = 0;
    unsigned short keylenMSB, keylenLSB, keylen, vallenMSB, vallenLSB, vallen = 0;
    KeyVal *hashtable[MAXHASHTABLEN];
}

这是一个使用RPC的练习，我们通过这种方式接收来自客户端的命令。最后我们调用 set() 函数:

unsigned char keybuf[MAXBUFFERLEN], valbuf[MAXBUFFERLEN] = {0};

while(1) { 
    sin_size =(socklen_t) sizeof(their_addr);
    new = accept(sock, (struct sockaddr *)&their_addr, &sin_size);
    if (new == -1) {
        perror("accept");
        continue;
    }

    inet_ntop(their_addr.ss_family, get_in_addr((struct sockaddr *)&their_addr), s, sizeof s);
    printf("server: got connection from %s\n", s);

        if((numbytes = recv(new, buffer, sizeof(buffer), 0)) < 0){
            perror("recv");
            exit(1);
        }
        printf("%d\n", numbytes);

        for(line = 0; line < numbytes; ++line){
            printf("Byte#%d = ",line);
            for(bitcounter = 0; bitcounter < 8; bitcounter++){
                printf("%d ", (buffer[line] >> bitcounter)&1);
            }
            printf("\n");
            switch(line){
                case 0: switch(buffer[line]) {
                            case 1: command = (buffer[line]); fprintf(stdout, "line = %d, command = %d\n", line, command); /*D*/ break;
                            case 2: command = (buffer[line]); fprintf(stdout, "line = %d, command = %d\n", line, command); /*S*/ break;
                            case 3: command = (buffer[line]); fprintf(stdout, "line = %d, command = %d\n", line, command); /*SD*/ break;
                            case 4: command = (buffer[line]); fprintf(stdout, "line = %d, command = %d\n", line, command); /*G*/ break;
                            case 5: command = (buffer[line]); fprintf(stdout, "line = %d, command = %d\n", line, command); /*GD*/ break;
                            case 6: command = (buffer[line]); fprintf(stdout, "line = %d, command = %d\n", line, command); /*SG*/ break;
                            case 7: command = (buffer[line]); fprintf(stdout, "line = %d, command = %d\n", line, command); /*SGD*/ break;
                            default: fprintf(stdout,"Not a valid command\n");   /*Fehlermeldung*/ break;
                }
                case 1: transid = buffer[line]; break;
                case 2: keylenMSB = buffer[line]; keylenMSB = keylenMSB << 8; break;
                case 3: keylenLSB = buffer[line]; keylen = keylenMSB|keylenLSB; ; break;
                case 4: vallenMSB = buffer[line]; vallenMSB = vallenMSB << 8; break;
                case 5: vallenLSB = buffer[line]; vallen = vallenMSB|vallenLSB; break;
                default: if(line < numbytes - vallen){
                        keybuf[line - 6] = buffer[line];
                } else if(vallen > 0){
                        valbuf[line-6-keylen] = buffer[line];       
                }
            }
        }

        switch(command){
            case 1: delete(hashtable, keybuf); /*D*/ break;
            case 2: set(hashtable, keybuf, valbuf); /*S*/ break;
            case 4: get(hashtable, keybuf, valbuf);  /*G*/ break;
            case 3: set(hashtable, keybuf, valbuf); delete(hashtable, keybuf); /*SD*/ break; 
            case 6: set(hashtable, keybuf, valbuf); get(hashtable, keybuf, valbuf); /*SG*/ break;
            case 5: get(hashtable, keybuf, valbuf); delete(hashtable, keybuf); /*GD*/ break;
            case 7: set(hashtable, keybuf, valbuf); get(hashtable, keybuf, valbuf); delete(hashtable, keybuf);  /*SGD*/ break;
            default: fprintf(stdout,"Unknown command.\n")/*Fehlermeldung*/; break;
        }
        buffer[0] = buffer[0]|0b00001000;
        send(new, buffer, sizeof(buffer), 0);
        for(line = 0; line < numbytes; ++line){
            printf("Sending Byte#%d = ",line);
            for(bitcounter = 0; bitcounter < 8; bitcounter++){
                printf("%d ", (buffer[line] >> bitcounter)&1);

Answer 1

我在您的代码中看到几个字符缓冲区，您是否尝试将它们用作键？例如，您可以像这样初始化它们:

char s[INET6_ADDRSTRLEN] = ""; 

此代码模拟完全相同的行为:

#include <stdio.h>

unsigned int hash(char *str) {
  unsigned int hash = 5381;
  int c;

  while ((c = *str++))
    hash = ((hash << 5) + hash) + c; /* hash * 33 + c */

  return hash % 128;
}

int main(int argc, char *argv[]) {
  char initialized[20] = "hello";
  printf("hash(initialized) = %u\n", hash(initialized));

  char not_initialized[20];
  printf("hash(not_initialized) = %u\n", hash(not_initialized));
  return 0;
}