openMP和數學庫的編譯問題

Question

我正在嘗試使用openMP編譯程序：

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

prog.c包括。 但是，當我運行./prog時，錯誤是：

bash: ./prog: Permission denied

我再次嘗試不帶-c標志：

gcc -o prog -fopenmp -lm prog.c

但是這一次似乎看不到數學庫中的函數，例如cos，sqrt（未定義的引用）。

#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

在第一種情況下， -c標志僅編譯為目標文件，而不是實際的可執行文件。 由於目標文件通常沒有設置可執行位（因為它們不能直接執行），因此會出現“ Permission denied錯誤。

在第二種情況下，這是因為指定-l庫的順序很重要。 您需要在prog.c文件之后移動-lm ，如下所示：

gcc -o prog -fopenmp prog.c -lm