c - 缓存 Sim 中的段错误

Question

我正在编写一个缓存模拟器。我运行 gdb 来找出我的段错误在哪里，它位于这个 for 循环中:

for (int i = 0; i < cache->numSets; ++i)
{
    for (int j = 0; j < cache->nLinesPerSet; ++j)
    {
        cache->sets[i].lines[j].valid = 0;
    }

}

这里是完整的代码，可帮助提供上下文并避免对问题可能出在哪里的任何假设。

谁能告诉我我的错误在哪里？ 谢谢!

#include "cache-sim.h"
#include <stdbool.h>
#include <stddef.h>
#include <malloc.h>
#include <time.h>
#include <stdlib.h>

/** Create and return a new cache-simulation structure for a
 *  cache for main memory withe the specified cache parameters params.
 *  No guarantee that *params is valid after this call.
 */

 /* GET SET ID 
         //calculate address tag and set index
        mem_addr_t addr_tag = addr >> (par.s + par.b);
        int tag_size = (64 - (par.s + par.b));
        unsigned long long temp = addr << (tag_size);
        unsigned long long setid = temp >> (tag_size + par.b); */


typedef struct CacheLineImpl{
    MemAddr addr;
    unsigned tag;
    int valid;
    int LRUVal;

}CacheLine;

typedef struct CacheSetImpl{
    CacheLine *lines;
    int numLines;
    unsigned mruHolder;

}CacheSet;

struct CacheSimImpl{
    CacheSet *sets;
    int numSets;
    //CacheParams params;
    unsigned nSetBits;          /** s # of seets is 2** this */
    unsigned nLinesPerSet;      /** E # of cache lines/ set */
    unsigned nLineBits;         /** b # of bytes/line is 2**this */
    unsigned nMemAddrBits;      /** m # of primary mem addr;
                                    total primary addr space is 2**this*/
    Replacement replacement;    /** replacement strategy*/

};


CacheSim *
new_cache_sim(const CacheParams *params)
{
    CacheSim *cache;
    cache = malloc(sizeof(*cache));  
    cache->nSetBits = params->nSetBits;
    cache->nLinesPerSet = params->nLinesPerSet;
    cache->nLineBits = params->nLineBits;
    cache->nMemAddrBits = params->nMemAddrBits;
    cache->replacement = params->replacement;

    //unsigned s = cache-> params.nSetBits;
    //unsigned E = cache-> params.nLinesPerSet;

    cache->numSets = (1 << cache->nSetBits));

    //malloc size of CachSimImpl struct
    cache->sets = malloc((cache->numSets)* (sizeof(*cache->sets)));
    cache->sets->lines = malloc(cache->nLinesPerSet* (sizeof(*cache->sets->lines)));

    for (int i = 0; i < cache->numSets; ++i)
    {
        for (int j = 0; j < cache->nLinesPerSet; ++j)
        {
            cache->sets[i].lines[j].valid = 0;
        }

    }



  return cache;
}

/** Free all resources used by cache-simulation structure *cache */
void
free_cache_sim(CacheSim *cache)
{
    //free all memory used
    free(cache->sets->lines);
    free(cache->sets);
    free(cache);
}


/** Return non-zero iff addr hits cache */
CacheResult
cache_sim_result(CacheSim *cache, MemAddr addr)
{
    CacheResult result  = { CACHE_MISS_WITH_REPLACE, 0x1234 };
    unsigned s = cache->nSetBits;
    unsigned E = cache->nLinesPerSet;
    unsigned b = cache->nLineBits;
    unsigned m = cache->nMemAddrBits;

    Replacement replace = cache->replacement;
    //cache->sets->lines->valid = 0;

    unsigned tagBits = m-(s+b);
    //printf("tagBits: %u", tagBits);

    unsigned tag = addr << (s + b);

    //printf("tag: %u", tag);

    unsigned temp = addr << (tagBits);
    //printf("temp: %u", temp);

    int setIndex = temp >> (tagBits +b);
    //printf("setIndex: %d", setIndex);

    time_t timer;
    srand((unsigned) time(&timer));


    bool validLine = true;
    for (int i = 0; i < E; ++i)
    {
        if(cache->sets[setIndex].lines[i].tag != tag){
            //track if a valid line exists in the set
            if(cache->sets[setIndex].lines[i].valid !=0){
                validLine = false;
            }
            else{
                validLine = true;
                cache->sets[setIndex].lines[i].valid = 1;
            }

        }

        else{
            result.status = CACHE_HIT;
            cache->sets->mruHolder = tag;
            break;
        }

    }

    if(validLine == true){
        for (int i = 0; i < E; ++i)
        {
            if(cache->sets[setIndex].lines[i].valid == 0){
                cache->sets[setIndex].lines[i].tag = tag;
                result.status = CACHE_MISS_WITHOUT_REPLACE;
                cache->sets->mruHolder = tag;
                break;
            }
        }


    }

    else{

        if (replace==LRU_R){ //replacement strategy is LRU

            int i = E - 1;
            cache->sets[setIndex].lines[i].tag = tag;
            result.status = CACHE_MISS_WITH_REPLACE;
            result.replaceAddr = addr;
            //break;
        }

        else if(replace==MRU_R){ //replacement strategy is MRU
            for (int i = 0; i < E; ++i)
            {
                if(cache->sets[setIndex].lines[i].tag ==
                    cache->sets->mruHolder){

                    cache->sets[setIndex].lines[i].tag=tag;
                    result.status = CACHE_MISS_WITH_REPLACE;
                    result.replaceAddr = addr;
                    cache->sets->mruHolder = tag;   
                    //break;
                }
            }
        }
        else{ //replacement strategy is Random

            int i = 0;
            i = rand () % E;
            cache->sets[setIndex].lines[i].tag = tag;
            result.status = CACHE_MISS_WITH_REPLACE;
            result.replaceAddr = addr;
            //break;

        }

    }




  return result;
}

Answer 1

问题是您为内部数组分配了错误的内存。

cache->sets = malloc((cache->numSets)* (sizeof(*cache->sets)));
cache->sets->lines = malloc(cache->nLinesPerSet* (sizeof(*cache->sets->lines)));

cache->sets->lines = ... 相当于 cache->sets[0].lines = ...，因此对于 i 大于 0，您将访问无效内存。

正确的方法可能是:

for (i = 0; i < cache->numSets; ++i) {
    cache->sets[i].lines = malloc(...);
}