Question

我试图用openMP编译程序：

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

prog.c包括。但是当我运行./prog时，错误是：

bash: ./prog: Permission denied

我在没有-c标志的情况下再次尝试：

gcc -o prog -fopenmp -lm prog.c

但这次它似乎没有看到数学库中的函数，如cos，sqrt（未定义的引用）。

#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

在第一种情况下，-c标志仅编译为对象文件，而不是实际的可执行文件。由于目标文件通常没有设置可执行位（因为它们不能直接执行），因此会出现Permission denied错误。

在第二种情况下，它是因为您指定-l库的顺序很重要。您需要在-lm文件之后移动prog.c，如下所示：

gcc -o prog -fopenmp prog.c -lm

编译openMP和数学库的问题

1 个答案: