env: gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu9)
app: Bin(main) calls
dynamic lib(testb.so), and testb.so contains a static lib(libtesta.a).
file list:
main.c
test.h
a.c
b.c
then compile as:
gcc -o testa.o -c a.c
ar -r libtesta.a testa.o
gcc -shared -fPIC -o testb.so b.c
gcc -o main main.c -L. -ltesta -ldl
then compile success, but runs an error:
./main: symbol lookup error: ./testb.so: undefined symbol: print
code as follows:
test.h
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <dlfcn.h>
int printa(const char *msg);
int printb(const char *msg);
a.c
#include "test.h"
int
printa(const char *msg)
{
printf("\tin printa\n");
printf("\t%s\n", msg);
}
b.c
#include "test.h"
int
printb(const char *msg)
{
printf("in printb\n");
printa("called by printb\n");
printf("%s\n", msg);
}
main.c
#include "test.h"
int
main(int argc, char **argv)
{
void *handle;
int (*dfn)(const char *);
printf("before dlopen\n");
handle = dlopen("./testb.so", RTLD_LOCAL | RTLD_LAZY);
printf("after dlopen\n");
if (handle == NULL) {
printf("dlopen fail: [%d][%s][%s]\n", \
errno, strerror(errno), dlerror());
exit(EXIT_FAILURE);
}
printf("before dlsym\n");
dfn = dlsym(handle, "printb");
printf("after dlsym\n");
if (dfn == NULL) {
printf("dlsym fail: [%d][%s][%s]\n", \
errno, strerror(errno), dlerror());
exit(EXIT_FAILURE);
}
printf("before dfn\n");
dfn("printb func\n");
printf("after dfn\n");
exit(EXIT_SUCCESS);
}
