問題，編譯OpenMP和數學庫

Question

我試圖編譯程序使用OpenMP：

gcc -c fopenmp -lm prog.c -o prog 

prog.c中包括。然而，當我運行./prog，錯誤的是：

bash: ./prog: Permission denied 

我再次嘗試不帶-c標誌：

gcc -o prog -fopenmp -lm prog.c 

但是這一次它似乎並沒有看到在數學庫中的函數像cos，sqrt（未定義參考）。

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <math.h> 
#include <time.h> 
#include <sys/time.h> 
#include <omp.h> 

#define REAL float 
#define NX (64) 
#ifndef M_PI 
#define M_PI (3.1415926535897932384626) 
#endif 


void init(REAL *buff, const int nx, const int ny, const int nz, 
      const REAL kx, const REAL ky, const REAL kz, 
      const REAL dx, const REAL dy, const REAL dz, 
      const REAL kappa, const REAL time) { 
    REAL ax, ay, az; 
    int jz, jy, jx; 
    ax = exp(-kappa*time*(kx*kx)); 
    ay = exp(-kappa*time*(ky*ky)); 
    az = exp(-kappa*time*(kz*kz)); 
    for (jz = 0; jz < nz; jz++) { 
    for (jy = 0; jy < ny; jy++) { 
     for (jx = 0; jx < nx; jx++) { 
     int j = jz*nx*ny + jy*nx + jx; 
     REAL x = dx*((REAL)(jx + 0.5)); 
     REAL y = dy*((REAL)(jy + 0.5)); 
     REAL z = dz*((REAL)(jz + 0.5)); 
     REAL f0 = (REAL)0.125 
      *(1.0 - ax*cos(kx*x)) 
      *(1.0 - ay*cos(ky*y)) 
      *(1.0 - az*cos(kz*z)); 
     buff[j] = f0; 
     } 
    } 
    } 
} 

REAL accuracy(const REAL *b1, REAL *b2, const int len) { 
    REAL err = 0.0; 
    int i; 
    for (i = 0; i < len; i++) { 
    err += (b1[i] - b2[i]) * (b1[i] - b2[i]); 
    } 
    return (REAL)sqrt(err/len); 
} 

typedef void (*diffusion_loop_t)(REAL *f1, REAL *f2, int nx, int ny, int nz, 
           REAL ce, REAL cw, REAL cn, REAL cs, REAL ct, 
           REAL cb, REAL cc, REAL dt, 
           REAL **f_ret, REAL *time_ret, int *count_ret); 

static void 
diffusion_baseline(REAL *f1, REAL *f2, int nx, int ny, int nz, 
        REAL ce, REAL cw, REAL cn, REAL cs, REAL ct, 
        REAL cb, REAL cc, REAL dt, 
        REAL **f_ret, REAL *time_ret, int *count_ret) { 
    REAL time = 0.0; 
    int count = 0; 

    do { 
    int z; 
    for (z = 0; z < nz; z++) { 
     int y; 
     for (y = 0; y < ny; y++) { 
     int x; 
     for (x = 0; x < nx; x++) { 
      int c, w, e, n, s, b, t; 
      c = x + y * nx + z * nx * ny; 
      w = (x == 0) ? c : c - 1; 
      e = (x == nx-1) ? c : c + 1; 
      n = (y == 0) ? c : c - nx; 
      s = (y == ny-1) ? c : c + nx; 
      b = (z == 0) ? c : c - nx * ny; 
      t = (z == nz-1) ? c : c + nx * ny; 
      f2[c] = cc * f1[c] + cw * f1[w] + ce * f1[e] 
       + cs * f1[s] + cn * f1[n] + cb * f1[b] + ct * f1[t]; 
     } 
     } 
    } 
    REAL *t = f1; 
    f1 = f2; 
    f2 = t; 
    time += dt; 
    count++; 
    } while (time + 0.5*dt < 0.1); 
    *time_ret = time; 
    *f_ret = f1; 
    *count_ret = count; 

    return; 
} 

static void 
diffusion_openmp(REAL *f1, REAL *f2, int nx, int ny, int nz, 
        REAL ce, REAL cw, REAL cn, REAL cs, REAL ct, 
        REAL cb, REAL cc, REAL dt, 
        REAL **f_ret, REAL *time_ret, int *count_ret) { 


#pragma omp parallel 
    { 
    REAL time = 0.0; 
    int count = 0; 
    REAL *f1_t = f1; 
    REAL *f2_t = f2; 

#pragma omp master 
    printf("%d threads running\n", omp_get_num_threads()); 

    do { 
     int z; 
#pragma omp for 
     for (z = 0; z < nz; z++) { 
     int y; 
     for (y = 0; y < ny; y++) { 
      int x; 
      for (x = 0; x < nx; x++) { 
      int c, w, e, n, s, b, t; 
      c = x + y * nx + z * nx * ny; 
      w = (x == 0) ? c : c - 1; 
      e = (x == nx-1) ? c : c + 1; 
      n = (y == 0) ? c : c - nx; 
      s = (y == ny-1) ? c : c + nx; 
      b = (z == 0) ? c : c - nx * ny; 
      t = (z == nz-1) ? c : c + nx * ny; 
      f2_t[c] = cc * f1_t[c] + cw * f1_t[w] + ce * f1_t[e] 
       + cs * f1_t[s] + cn * f1_t[n] + cb * f1_t[b] + ct * f1_t[t]; 
      } 
     } 
     } 
     REAL *t = f1_t; 
     f1_t = f2_t; 
     f2_t = t; 
     time += dt; 
     count++; 
    } while (time + 0.5*dt < 0.1); 
#pragma omp master 
    { 
     *f_ret = f1_t; 
     *time_ret = time;  
     *count_ret = count;   
    } 
    } 

    return; 
} 


int main(int argc, char *argv[]) 
{ 

    struct timeval time_begin, time_end; 

    int nx = NX; 
    int ny = NX; 
    int nz = NX; 
    REAL *f1 = (REAL *)malloc(sizeof(REAL)*NX*NX*NX); 
    REAL *f2 = (REAL *)malloc(sizeof(REAL)*NX*NX*NX); 

    REAL time = 0.0; 
    int count = 0; 

    REAL l, dx, dy, dz, kx, ky, kz, kappa, dt; 
    REAL ce, cw, cn, cs, ct, cb, cc; 

    l = 1.0; 
    kappa = 0.1; 
    dx = dy = dz = l/nx; 
    kx = ky = kz = 2.0 * M_PI; 
    dt = 0.1*dx*dx/kappa; 

    init(f1, nx, ny, nz, kx, ky, kz, dx, dy, dz, kappa, time); 

    ce = cw = kappa*dt/(dx*dx); 
    cn = cs = kappa*dt/(dy*dy); 
    ct = cb = kappa*dt/(dz*dz); 
    cc = 1.0 - (ce + cw + cn + cs + ct + cb); 

    diffusion_loop_t diffusion_loop = diffusion_baseline; 
    if (argc == 2) { 
    if (strcmp(argv[1], "openmp") == 0) { 
     diffusion_loop = diffusion_openmp; 
    } 
    } 

    gettimeofday(&time_begin, NULL); 
    diffusion_loop(f1, f2, nx, ny, nz, ce, cw, cn, cs, ct, cb, cc, dt, 
       &f1, &time, &count); 
    gettimeofday(&time_end, NULL); 

    REAL *answer = (REAL *)malloc(sizeof(REAL) * nx*ny*nz); 
    init(answer, nx, ny, nz, kx, ky, kz, dx, dy, dz, kappa, time); 

    REAL err = accuracy(f1, answer, nx*ny*nz); 
    double elapsed_time = (time_end.tv_sec - time_begin.tv_sec) 
     + (time_end.tv_usec - time_begin.tv_usec)*1.0e-6; 
    REAL mflops = (nx*ny*nz)*13.0*count/elapsed_time * 1.0e-06; 
    double thput = (nx * ny * nz) * sizeof(REAL) * 2.0 * count 
    /elapsed_time/(1 << 30); 

    fprintf(stderr, "elapsed time : %.3f (s)\n", elapsed_time); 
    fprintf(stderr, "flops  : %.3f (MFlops)\n", mflops); 
    fprintf(stderr, "throughput : %.3f (GB/s)\n", thput); 
    fprintf(stderr, "accuracy  : %e\n", err); 
    free(answer); 
    free(f1); 
    free(f2); 
    return 0; 
} 

Answer 1

在你的第一種情況，-c標誌只編譯成一個對象文件，而不是實際的可執行文件。由於目標文件通常不會設置可執行位（因爲它們不能直接執行），所以會出現Permission denied錯誤。

在第二種情況下，這是因爲您指定-l庫的順序非常重要。你需要你的prog.c文件之後，移動-lm，像這樣：

gcc -o prog -fopenmp prog.c -lm