Linux 애플리케이션을 위한 DLL 작성하기

plugin 작성으로 전체 애플리케이션 구현 효과 얻기

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);
}

Allen Wilson 은 IBM에서 e-business 아키텍트 겸 컨설턴트로 일하고 있다. 또한, Linux, AIX, WebSphere Application Server, 애플리케이션 호스팅 전문가이다.