为 Linux 应用程序编写 DLL

为 Linux 应用程序编写 DLL

main()
{
   printf("Hello world
");
}

libc.so.6 => /lib/libc.so.6 (0x4001d000)
         /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)

dlTest  2-Original message 
HeLlO WoRlD
    dlTest  3-Open Library with absolute path return-(null)- 
    dlTest  4-Find symbol printUPPERCASE return-(null)- 
HELLO WORLD
    dlTest  5-printUPPERCASE return-(null)- 
    dlTest  6-Close handle return-(null)-
    dlTest  7-Open Library with relative path return-(null)- 
    dlTest  8-Find symbol printLowercase return-(null)- 
hello world
    dlTest  9-printLowercase return-(null)- 
    dlTest 10-Close handle return-(null)-

#!/bin/ksh
#  Build shared library
#
#set -x
clear
#
#  Shared library for dlopen absolute path test
#
if [ -f UPPERCASE.o ]; then rm UPPERCASE.o
fi
gcc  -c -fpic UPPERCASE.c
if [ -f UPPERCASE.so ]; then rm UPPERCASE.so
fi
gcc -shared -lc  -o UPPERCASE.so  UPPERCASE.o 
#
#  Shared library for dlopen relative path test
#
export LD_LIBRARY_PATH=`pwd`
if [ -f lowercase.o ]; then rm lowercase.o
fi
gcc  -c -fpic lowercase.c
if [ -f lowercase.so ]; then rm lowercase.so
fi
gcc -shared -lc  -o lowercase.so  lowercase.o
#
#  Rebuild test program
#
if [ -f dlTest ]; then rm dlTest
fi
gcc -o dlTest dlTest.c -ldl
echo Current LD_LIBRARY_PATH=$LD_LIBRARY_PATH
dlTest

/*************************************************************/
/*     Test Linux Dynamic Function Loading              */
/*                                      */
/*     void       *dlopen(const char *filename, int flag)           */
/*          Opens dynamic library and return handle     */
/*                                      */
/*     const char *dlerror(void)                    */
/*          Returns string describing the last error.           */
/*                                      */
/*     void       *dlsym(void *handle, char *symbol)            */
/*          Return pointer to symbol's load point.          */
/*          If symbol is undefined, NULL is returned.           */
/*                                      */
/*     int        dlclose (void *handle)                    */
/*          Close the dynamic library handle.               */
/*                                      */
/*                                      */
/*                                      */
/*************************************************************/
#include<stdio.h>
#include    <stdlib.h>
 
/*                              */
/* 1-dll include file and variables */
/*                              */
#include    <dlfcn.h>
void  *FunctionLib;     /*  Handle to shared lib file   */
int   (*Function)();        /*  Pointer to loaded routine   */
const char *dlError;        /*  Pointer to error string     */
main( argc, argv )
{
  int   rc;             /*  return codes            */
  char HelloMessage[] = "HeLlO WoRlD\n";
 
/*                              */
/* 2-print the original message                 */
/*                              */
  printf("  dlTest  2-Original message \n");
  printf("%s", HelloMessage);
/*                                               */
/*  3-Open Dynamic Loadable Libary with absolute path      */
/*                                              */
  FunctionLib = dlopen("/home/dlTest/UPPERCASE.so",RTLD_LAZY);
  dlError = dlerror();
  printf("  dlTest  3-Open Library with absolute path return-%s- \n", dlError);
  if( dlError ) exit(1);
/*                              */
/* 4-Find the first loaded function */
/*                              */
  Function    = dlsym( FunctionLib, "printUPPERCASE");
  dlError = dlerror();
  printf("  dlTest  4-Find symbol printUPPERCASE return-%s- \n", dlError);
  if( dlError ) exit(1);
/*                              */
/* 5-Execute the first loaded function              */
/*                              */
  rc = (*Function)( HelloMessage );
  printf("  dlTest  5-printUPPERCASE return-%s- \n", dlError);
/*                              */
/* 6-Close the shared library handle                    */
/* Note:  after the dlclose, "printUPPERCASE" is not loaded     */
/*                              */
  rc = dlclose(FunctionLib);
  dlError = dlerror();
  printf("  dlTest  6-Close handle return-%s-\n",dlError); 
  if( rc ) exit(1);
/*                              */
/*  7-Open Dynamic Loadable Libary using LD_LIBRARY path        */
/*                              */
  FunctionLib = dlopen("lowercase.so",RTLD_LAZY);
  dlError = dlerror();
  printf("  dlTest  7-Open Library with relative path return-%s- \n", dlError);
  if( dlError ) exit(1);
/*                              */
/* 8-Find the second loaded function                */
/*                              */
  Function    = dlsym( FunctionLib, "printLowercase");
  dlError = dlerror();
  printf("  dlTest  8-Find symbol printLowercase return-%s- \n", dlError);
  if( dlError ) exit(1);
/*                              */
/* 8-execute the second loaded function             */
/*                              */
  rc = (*Function)( HelloMessage );
  printf("  dlTest  9-printLowercase return-%s- \n", dlError);
/*                              */
/* 10-Close the shared library handle               */
/*                              */
  rc = dlclose(FunctionLib);
  dlError = dlerror();
  printf("  dlTest 10-Close handle return-%s-\n",dlError); 
  if( rc ) exit(1);
  return(0);
}

/************************************************/
/*      Function to print input string as UPPER case.         */
/*      Returns 1.                                                            */
/*********************************************** */
int printUPPERCASE ( inLine )
char inLine[];
{
   char UPstring[256];
   char *inptr, *outptr;
   
   inptr = inLine;
   outptr = UPstring;
   while ( *inptr != '\0' )
      *outptr++ = toupper(*inptr++);
  *outptr++ = '\0';
   printf(UPstring);
   return(1);
}

/********************************************/
/*     Function to print input string as lower case.      */
/*     Returns 2.                                                      */
/******************************************* */
int printLowercase( inLine )
char inLine[];
{
   char lowstring[256];
   char *inptr, *outptr;
   inptr = inLine;
   outptr = lowstring;
   while ( *inptr != '' )
      *outptr++ = tolower(*inptr++);
  *outptr++ = '';
   printf(lowstring);
   return(2);
}