[英]Difference in behavior between clang and gcc?
我正在編寫一個C函數來模擬給定地址跟蹤的緩存。 使用gcc(確實是clang)在我的Mac上編譯時,該功能按預期工作。 我的Mac上的gcc --version
返回以下內容:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 8.1.0 (clang-802.0.42)
當我使用gcc在linux上編譯同一程序時,返回值很低,並且程序中的eC和hC(高速緩存逐出計數器和命中計數器)成千上萬,應該低於10。輸入gcc- -version在linux機器上,它返回以下內容:
gcc(Ubuntu 4.9.3-8ubuntu2〜14.04)4.9.3
這是程序:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <limits.h>
#include <getopt.h>
#include "cachelab.h"
typedef struct{
int v;
int t;
int LRU;
} block;
typedef struct{
block *blocks;
} set;
typedef struct{
set *sets;
} cache;
void simulate(int s, int E, int b, char* file, int* hC, int* mC, int* eC)
{
int numSets = (1 << s);
char operation;
int address;
int size;
int curTag;
int curSet;
int maxLRU = 0;
int curLRU = 0;
int check = 0;
cache c;
set *sets = malloc(sizeof(set) * numSets);
c.sets = sets;
int i = 0;
while(i < numSets)
{
c.sets[i].blocks = malloc(sizeof(block) * E);
for (int j = 0; j < E; j++)
{
c.sets[i].blocks[j].v = 0;
c.sets[i].blocks[j].t = INT_MIN;
c.sets[i].blocks[j].LRU = 0;
}
i++;
}
FILE *f = fopen(file, "r");
while(fscanf(f," %c %x,%d", &operation, &address, &size) != EOF)
{
check = 0;
curTag = ((unsigned int) address) >> (s+b);
curSet = (address >> b) & ((1 << s) - 1);
for (int i = 0; i < E; i++)
{
c.sets[curSet].blocks[i].LRU++;
if(c.sets[curSet].blocks[i].LRU >= maxLRU)
{
maxLRU = c.sets[curSet].blocks[i].LRU;
curLRU = i;
}
if(curTag == c.sets[curSet].blocks[i].t)
{
*hC = *hC + 1;
if (operation == 'M')
{
*hC = *hC + 1;
}
c.sets[curSet].blocks[i].LRU = 0;
check = 1;
}
}
if(check == 0)
{
for(int i = 0; i < E; i++)
{
if(c.sets[curSet].blocks[i].v == 0)
{
*mC = *mC + 1;
if (operation == 'M')
{
*hC = *hC + 1;
}
c.sets[curSet].blocks[i].v = 1;
c.sets[curSet].blocks[i].LRU = 0;
c.sets[curSet].blocks[i].t = curTag;
check = 1;
break;
}
}
}
if(check == 0)
{
*eC = *eC + 1;
*mC = *mC + 1;
if (operation == 'M')
{
*hC = *hC + 1;
}
c.sets[curSet].blocks[curLRU].t = curTag;
c.sets[curSet].blocks[curLRU].v = 1;
c.sets[curSet].blocks[curLRU].LRU = 0;
}
}
}
int main(int argc, char** argv)
{
int hitCount, missCount, evictionCount;
int s, E, b;
char *file;
char opt;
while((opt = getopt(argc,argv,"v:h:s:E:b:t:")) != -1)
{
switch(opt){
case 'v':
break;
case 'h':
break;
case 's':
s = atoi(optarg);
break;
case 'E':
E = atoi(optarg);
break;
case 'b':
b = atoi(optarg);
break;
case 't':
file = optarg;
break;
default:
exit(1);
}
}
simulate(s, E, b, file, &hitCount, &missCount, &evictionCount);
printSummary(hitCount, missCount, evictionCount);
return 0;
}
編輯:
我知道這是由於clang和gcc之間的差異。 有人知道我如何解決此差異嗎?
這是cachelab.c:
/*
* cachelab.c - Cache Lab helper functions
*/
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include "cachelab.h"
#include <time.h>
trans_func_t func_list[MAX_TRANS_FUNCS];
int func_counter = 0;
/*
* printSummary - Summarize the cache simulation statistics. Student cache simulators
* must call this function in order to be properly autograded.
*/
void printSummary(int hits, int misses, int evictions)
{
printf("hits:%d misses:%d evictions:%d\n", hits, misses, evictions);
FILE* output_fp = fopen(".csim_results", "w");
assert(output_fp);
fprintf(output_fp, "%d %d %d\n", hits, misses, evictions);
fclose(output_fp);
}
/*
* initMatrix - Initialize the given matrix
*/
void initMatrix(int M, int N, int A[N][M], int B[M][N])
{
int i, j;
srand(time(NULL));
for (i = 0; i < N; i++){
for (j = 0; j < M; j++){
// A[i][j] = i+j; /* The matrix created this way is symmetric */
A[i][j]=rand();
B[j][i]=rand();
}
}
}
void randMatrix(int M, int N, int A[N][M]) {
int i, j;
srand(time(NULL));
for (i = 0; i < N; i++){
for (j = 0; j < M; j++){
// A[i][j] = i+j; /* The matrix created this way is symmetric */
A[i][j]=rand();
}
}
}
/*
* correctTrans - baseline transpose function used to evaluate correctness
*/
void correctTrans(int M, int N, int A[N][M], int B[M][N])
{
int i, j, tmp;
for (i = 0; i < N; i++){
for (j = 0; j < M; j++){
tmp = A[i][j];
B[j][i] = tmp;
}
}
}
/*
* registerTransFunction - Add the given trans function into your list
* of functions to be tested
*/
void registerTransFunction(void (*trans)(int M, int N, int[N][M], int[M][N]),
char* desc)
{
func_list[func_counter].func_ptr = trans;
func_list[func_counter].description = desc;
func_list[func_counter].correct = 0;
func_list[func_counter].num_hits = 0;
func_list[func_counter].num_misses = 0;
func_list[func_counter].num_evictions =0;
func_counter++;
}
您忘記了初始化計數器和標志,因此它們以未定義的值開始。 以下幾行:
int hitCount, missCount, evictionCount;
int s, E, b;
應該:
int hitCount = 0, missCount = 0, evictionCount = 0;
int s = 0, E = 0, b = 0;
碰巧Mac上的初始值恰好較低,因此您在Mac上也無法獲得正確的結果(至少不能保證,因為初始值未定義)。
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