用pwnable.kr 17解决工作-memcpy。 数据对齐

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 // compiled with : gcc -o memcpy memcpy.c -m32 -lm #include <stdio.h> #include <string.h> #include <stdlib.h> #include <signal.h> #include <unistd.h> #include <sys/mman.h> #include <math.h> unsigned long long rdtsc(){ asm("rdtsc"); } char* slow_memcpy(char* dest, const char* src, size_t len){ int i; for (i=0; i<len; i++) { dest[i] = src[i]; } return dest; } char* fast_memcpy(char* dest, const char* src, size_t len){ size_t i; // 64-byte block fast copy if(len >= 64){ i = len / 64; len &= (64-1); while(i-- > 0){ __asm__ __volatile__ ( "movdqa (%0), %%xmm0\n" "movdqa 16(%0), %%xmm1\n" "movdqa 32(%0), %%xmm2\n" "movdqa 48(%0), %%xmm3\n" "movntps %%xmm0, (%1)\n" "movntps %%xmm1, 16(%1)\n" "movntps %%xmm2, 32(%1)\n" "movntps %%xmm3, 48(%1)\n" ::"r"(src),"r"(dest):"memory"); dest += 64; src += 64; } } // byte-to-byte slow copy if(len) slow_memcpy(dest, src, len); return dest; } int main(void){ setvbuf(stdout, 0, _IONBF, 0); setvbuf(stdin, 0, _IOLBF, 0); printf("Hey, I have a boring assignment for CS class.. :(\n"); printf("The assignment is simple.\n"); printf("-----------------------------------------------------\n"); printf("- What is the best implementation of memcpy? -\n"); printf("- 1. implement your own slow/fast version of memcpy -\n"); printf("- 2. compare them with various size of data -\n"); printf("- 3. conclude your experiment and submit report -\n"); printf("-----------------------------------------------------\n"); printf("This time, just help me out with my experiment and get flag\n"); printf("No fancy hacking, I promise :D\n"); unsigned long long t1, t2; int e; char* src; char* dest; unsigned int low, high; unsigned int size; // allocate memory char* cache1 = mmap(0, 0x4000, 7, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); char* cache2 = mmap(0, 0x4000, 7, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); src = mmap(0, 0x2000, 7, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); size_t sizes[10]; int i=0; // setup experiment parameters for(e=4; e<14; e++){ // 2^13 = 8K low = pow(2,e-1); high = pow(2,e); printf("specify the memcpy amount between %d ~ %d : ", low, high); scanf("%d", &size); if( size < low || size > high ){ printf("don't mess with the experiment.\n"); exit(0); } sizes[i++] = size; } sleep(1); printf("ok, lets run the experiment with your configuration\n"); sleep(1); // run experiment for(i=0; i<10; i++){ size = sizes[i]; printf("experiment %d : memcpy with buffer size %d\n", i+1, size); dest = malloc( size ); memcpy(cache1, cache2, 0x4000); // to eliminate cache effect t1 = rdtsc(); slow_memcpy(dest, src, size); // byte-to-byte memcpy t2 = rdtsc(); printf("ellapsed CPU cycles for slow_memcpy : %llu\n", t2-t1); memcpy(cache1, cache2, 0x4000); // to eliminate cache effect t1 = rdtsc(); fast_memcpy(dest, src, size); // block-to-block memcpy t2 = rdtsc(); printf("ellapsed CPU cycles for fast_memcpy : %llu\n", t2-t1); printf("\n"); } printf("thanks for helping my experiment!\n"); printf("flag : ----- erased in this source code -----\n"); return 0; }