Sometimes you will want to know what a binary file contains (functions, arrays, objects) etc. The ‘nm’ command will do that for you, and the following 1-liner will sort the output by size. I use this to determine why some source compiled on Solaris is larger than when compiled in linux.

e.g.

 nm  | sort -n -t \| +2

Here is a small binary I happen to have.

$ nm write_random | sort -n -t \| +2 

write_random:

[Index]   Value      Size    Type  Bind  Other Shndx   Name
..

..
[72]    | 134520544|      60|OBJT |GLOB |0    |23     |tstr
[85]    |         0|      60|FUNC |GLOB |0    |UNDEF  |lseek@@GLIBC_2.0
[58]    | 134515432|      66|FUNC |GLOB |0    |12     |__libc_csu_fini
[66]    |         0|      67|FUNC |GLOB |0    |UNDEF  |getopt@@GLIBC_2.0
[74]    | 134515348|      82|FUNC |GLOB |0    |12     |__libc_csu_init
[51]    |         0|     113|FUNC |GLOB |0    |UNDEF  |close@@GLIBC_2.0
[76]    |         0|     113|FUNC |GLOB |0    |UNDEF  |fsync@@GLIBC_2.0
[50]    |         0|     124|FUNC |GLOB |0    |UNDEF  |write@@GLIBC_2.0
[88]    |         0|     124|FUNC |GLOB |0    |UNDEF  |open@@GLIBC_2.0
[55]    | 134514968|     163|FUNC |GLOB |0    |12     |getSizeInBlocks
[68]    | 134515131|     214|FUNC |GLOB |0    |12     |do_writes
[89]    |         0|     217|FUNC |GLOB |0    |UNDEF  |exit@@GLIBC_2.0
[79]    |         0|     221|FUNC |GLOB |0    |UNDEF  |__libc_start_main@@GLIBC_2.0
[67]    |         0|     344|FUNC |GLOB |0    |UNDEF  |__fxstat@@GLIBC_2.0
[53]    |         0|     523|FUNC |GLOB |0    |UNDEF  |perror@@GLIBC_2.0
[62]    |         0|     539|FUNC |GLOB |0    |UNDEF  |malloc@@GLIBC_2.0
[77]    | 134514424|     544|FUNC |GLOB |0    |12     |main

Here’s the source code for the same binary, notice in the output of nm the size of the object tstr is 60 bytes, and in the code it’s specified as char[60].

$ cat write_random.c
#include 
#include 
#include 
#include 
#include 
#include 

#define ARRAYSIZE 16*1024
#define NUMTOWRITE 10

int getSizeInBlocks(int,int, char *);
void do_writes(int,int, int);
int     loopsToDo=1;
int     limitLoops=0;   /*Default to doing loops forever*/
int     msPause=0;
int     iostart,iostop,iotimeMS,ioThresh;
struct tm *tm_ptr;
time_t  tm;
char    tstr[60];
int     IOoverThresh=1,TotalIOs=1,dofsync=0,forcesize=0;
double  badpct;

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

        int     i,n,count=0,SizeInBlocks;
        int     appBlockSize=8192,key;  /*Default IO size is 8k*/
        int     mode=O_RDWR;
        int     dsync=0;
        char    *array,c,filename[255];
        int fd;

        if (argc == 1) {
                fprintf(stderr,"Usage: [-d  -f | -b  |-s | -l  | -o st_size; */
  FileSize=lseek(fd,0,SEEK_END);
  if (forcesize)
    FileSize=forcesize*1024*1024;
  appBlocks = (int) FileSize/appBlockSize;
  printf("file %s is %d bytes %d application blocks blocksize = %d\n",filename,FileSize,appBlocks,appBlockSize);
  return appBlocks;
}

void do_writes(int fd,int appBlockSize, int appBlocks)
{
 char *array;
 array=malloc(appBlockSize);

 while  (loopsToDo >0 ){
  /*generate a random number 0-appBlocks*/
  int seek_val=rand()%appBlocks;
  lseek(fd,appBlockSize * seek_val, SEEK_SET);
  write(fd,array, appBlockSize);
  if (dofsync)
    fsync(fd);
  TotalIOs++;

  if (limitLoops)
        loopsToDo--;
  if (msPause)
        usleep(msPause*1000);
  }
  return;
}

Tags: binary, compiler, linux, nm, solaris, sort