I have an executable (1) with two shared objects (2 and 3) opened using dlopen(..., RTLD_GLOBAL). All files include the symbol func().
If I use dlsym(RTLD_NEXT, ...) in 1 looking for the next func() symbol, the 2 symbol is returned. But, if in 2 I use dlsym(RTLD_NEXT) again, no symbol is found. I thought that 3 symbol would be returned.
What is the meaning of this?
Update: adding an example
#define _GNU_SOURCE
#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
typedef void (*next_t) (void);
static char *name[] = { "next" };
static char path[1024];
static next_t linc;
static void dlnext_open(int i)
{
sprintf(path, "./lib%d.so", i);
fprintf(stderr, "loading %d\n", i);
void *handler = dlopen(path, RTLD_GLOBAL | RTLD_NOW);
return;
}
int next()
{
fprintf(stderr, "NEXT %d\n", NUM);
#ifdef DLNUM1
dlnext_open(DLNUM1);
#endif
#ifdef DLNUM2
dlnext_open(DLNUM2);
#endif
linc = dlsym(RTLD_NEXT, name[0]);
if (linc != NULL) {
linc();
fprintf(stderr, "returning to %d\n", NUM);
} else {
fprintf(stderr, "no next\n");
}
}
#if NUM == 1
int main(int argc, char *argv[])
{
next();
return 0;
}
#endif
And the make/exec:
gcc -O0 -shared -fPIC -o lib3.so 1.c -DNUM=3
gcc -O0 -shared -fPIC -o lib2.so 1.c -DNUM=2
gcc -O0 -o 1 1.c -ldl -DNUM=1 -DDLNUM1=2 -DDLNUM2=3
./1
The result:
NEXT 1
loading 2
loading 3
NEXT 2
no next
returning to 1
Related
After some googling, I got shared libraries working quite well. I can open my module with dlopen and load functions with dlsym. However, this is always running functions from the library in the program, how do I use functions from my program in the library?
My simplified code:
main.c
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
int twice(int a){
return a*2;
}
int main(int argc, char ** argv){
char *plugin_name;
void *plugin;
int (*init)();
if(argc<2){
printf("give lib name\n");
return 0;
}
plugin = dlopen (argv[1], RTLD_NOW);
if (!plugin)
{
printf("Cannot load %s: %s\n",argv[1], dlerror ());
return 0;
}
init = dlsym (plugin, "init");
char * result = dlerror ();
if (result)
{
printf("Cannot find init in %s: %s\n", plugin_name, result);
return 0;
}
int res = init();
printf("result: %i\n",res);
return 0;
}
plugin.c
int init()
{
return twice(4);
}
Makefile:
all: main lib
main: main.c
gcc -ldl -o main main.c
lib: plugin.c
gcc -shared -o plugin.so plugin.c
And I run it with:
./main ./plugin.so
With Linux, glibc, and GNU ld you can run -rdynamic to your executable link flags. This will make all symbols in your executable visible to loadable modules, as if it were a shared library.
Note that this is not necessarily portable to other Unix-like systems.
I want to compile following c file:
#include <stdio.h>
#include <stdlib.h>
#include <../deps/linux/gpio.h>
int main(void) {
int r = gpio_is_valid(31);
if (r == -1) {
perror("GPIO address is invalid.\n");
exit(EXIT_FAILURE);
}
return EXIT_SUCCESS;
}
My Makefile looks as
build: gpio
LDFLAGS = -Llinux
gpio:
$(CC) -o gpio.o src/gpio.c $(LDFLAGS)
Unfortunately I get "gpio.h not found" as error.
gpio.h is a Linux kernel header. It can not be used for user space programs.
Trying to compile an example of wrapping library from here
I had to include stdio.h and stdlib.h, and came to that code:
#define _GNU_SOURCE
#define _USE_GNU
#include <signal.h>
#include <execinfo.h>
#include <stdlib.h>
#include <stdio.h>
#include <dlfcn.h>
static void show_stackframe() {
void *trace[16];
char **messages = (char **)NULL;
int i, trace_size = 0;
trace_size = backtrace(trace, 16);
messages = backtrace_symbols(trace, trace_size);
printf("[bt] Execution path:\n");
for (i=0; i < trace_size; ++i)
printf("[bt] %s\n", messages[i]);
}
int ioctl(int fd, int request, void *data)
{
char *msg;
if (next_ioctl == NULL) {
fprintf(stderr, "ioctl : wrapping ioctl\n");
fflush(stderr);
// next_ioctl = dlsym((void *) -11, /* RTLD_NEXT, */ "ioctl");
next_ioctl = dlsym(RTLD_NEXT, "ioctl");
fprintf(stderr, "next_ioctl = %p\n", next_ioctl);
fflush(stderr);
if ((msg = dlerror()) != NULL) {
fprintf(stderr, "ioctl: dlopen failed : %s\n", msg);
fflush(stderr);
exit(1);
} else
fprintf(stderr, "ioctl: wrapping done\n");
fflush(stderr);
}
if (request == 1) { /* SCSI_IOCTL_SEND_COMMAND ? */
/* call back trace */
fprintf(stderr, "SCSI_IOCTL_SEND_COMMAND ioctl\n");
fflush(stderr);
show_stackframe();
}
return next_ioctl(fd, request, data);
}
and Makefile
#
# Makefile
#
all: libs test_ioctl
libs: libwrap_ioctl.so
libwrap_ioctl.so: wrap_ioctl.c
rm -f libwrap_ioctl.so*
gcc -fPIC -shared -Wl,-soname,libwrap_ioctl.so.1 -ldl -o libwrap_ioctl.so.1.0 wrap_ioctl.c
ln -s libwrap_ioctl.so.1.0 libwrap_ioctl.so.1
ln -s libwrap_ioctl.so.1 libwrap_ioctl.so
clean:
rm -f libwrap_ioctl.so* test_ioctl
and stuck in these errors, despite dlfcn.h is included.
~/my_src/native/glibc_wrapper > make
rm -f libwrap_ioctl.so*
gcc -fPIC -shared -Wl,-soname,libwrap_ioctl.so.1 -ldl -o libwrap_ioctl.so.1.0 wrap_ioctl.c
wrap_ioctl.c: In function ‘ioctl’:
wrap_ioctl.c:26: error: ‘next_ioctl’ undeclared (first use in this function)
wrap_ioctl.c:26: error: (Each undeclared identifier is reported only once
wrap_ioctl.c:26: error: for each function it appears in.)
make: *** [libwrap_ioctl.so] Ошибка 1
dlfcn.h itself doesn't define any symbol with name next_smth. (In SUS, dlfcn.h only defines several dl* functions and RTLD_ macro: http://pubs.opengroup.org/onlinepubs/7908799/xsh/dlfcn.h.html)
You should define this as pointer to function in your program code in explicit way. Something like this: (taken from https://port70.net/svn/misc/remac/remac.c or from https://github.com/itm/forward-sensor/blob/master/preload.c or ... any google search for "next_ioctl"):
static int (*next_ioctl) (int fd, int request, void *data) = NULL;
Or, if you want a collective blog-reading session, there is additional line in the blog post with ioctl overloading: http://scaryreasoner.wordpress.com/2007/11/17/using-ld_preload-libraries-and-glibc-backtrace-function-for-debugging/ (just before first huge code fragment)
Then, declare a function pointer to hold the value
of the “real” ioctl() function from glibc:
static int (*next_ioctl)(int fd, int request, void *data) = NULL;
Then declare your replacement ioctl function:
You missed to declare next_ioctl.
Just add
void * next_ioctl = NULL;
int (*next_ioctl) (int, int, ...) = NULL;
to main().
I have to compile two independent processes-sendfdsock.c and recvfdsock.c using make file. Both the files have there own main function. This means they are independent and I have to compile them as two different binaries. This is my make file:
compileAll:sendfdsock recvfdsock
sendfdsock:sendfdsock.o
gcc -o sendfdsock sendfdsock.o
sendfdsock.o:sendfdsock.c accessories.h
gcc -c sendfdsock.c
recvfdsock.o:recvfdsock.c accessories.h
gcc -c recvfdsock.c
recvfdsock:recvfdsock.o
gcc -o recvfdsock recvfdsock.o
Here I have made a compileAll target which compiles both the files.
Both files need to use accessories.h. As mention in GNU Make Doc - A simple Make file. I wrote this make file.
accessories.h :
#include <malloc.h>
#include <time.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <pthread.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <error.h>
#include <signal.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <stropts.h>
#define PORT "4444" //port we are listening on
int sendall(int fd, char *buf, int *len);
int recvall(int fd, char *buf, int *len);
void logp(int typ, char* msg);
void errorp(char *where, int boolean, int errn,char *what);
accessories.c :
#include "accessories.h"
void logp(int typ, char* msg) // typ --> type(category) of message [1-Normal Log, 2-Warning(any unexpected thing happened), 3-Error, 4-Debugging Log ]
{
int fd;
time_t now;
ssize_t wlength=0;
char * dat;
char * str;
int size = 45+strlen(msg);//14+24+5+sizeof msg+1
str= (char *) malloc(size);
time(&now);//system time in seconds
dat = ctime(&now); // converting seconds to date-time format
dat = strtok(dat,"\n");
//Appending type of log
switch(typ)
{
case 1:
strcpy(str,"__LOG__ | ");
strcat(str,dat);
break;
case 2:
strcpy(str,"__WARN__ | ");
strcat(str,dat);
break;
case 3:
strcpy(str,"__ERR__ | ");
strcat(str,dat);
break;
case 4:
strcpy(str,"__DEBUG__ | ");
strcat(str,dat);
break;
default:
strcpy(str,"__UNDEF__ | ");
strcat(str,dat);
break;
}
strcat(str," | ");
strcat(str,msg);//appending message
strcat(str,"\n");
fd = open("log", O_WRONLY | O_CREAT | O_APPEND, 0644); // should be opened somewhere else
if (fd == -1)
printf("Could not open log - %s\n",strerror(errno));
else
{//need to add lock to the file and printing error message
while ( wlength < strlen(str) )
{
wlength = write(fd, str,strlen(str));
if (wlength == -1)
{
printf("Error : writing log\n");
break;
}
}
}
}
int sendall(int fd, char *buf, int *len)
{
int total = 0; // how many bytes we've sent
int bytesleft = *len; // how many we have left to send
int n;
while(total < *len) {
n = send(fd, buf+total, bytesleft, 0);
if (n == -1) { break; }
total += n;
bytesleft -= n;
}
*len = total; // return number actually sent here
return n==-1?-1:0; // return -1 on failure, 0 on success
}
int recvall(int fd, char *buf, int *len)
{
int total = 0; // how many bytes we've sent
int bytesleft = *len; // how many we have left to send
int n;
while(total < *len) {
n = recv(fd, buf+total, bytesleft, 0);
if (n == -1) { break; }
total += n;
bytesleft -= n;
}
*len = total; // return number actually sent here
return n==-1?-1:0; // return -1 on failure, 0 on success
}
void errorp(char *where, int boolean, int errn,char *what)
{
char errmsg[21+strlen(where)];
strcpy(errmsg,"Where - ");
strcat(errmsg,where);
strcat(errmsg," | Error - ");
if(boolean == 1)//we got error number
{
strcat(errmsg,strerror(errn));
//fprintf(stderr,"ERROR - In %s and error is %s\n",where ,strerror(errn));
logp(3,errmsg);
}
else if(boolean == 0)//we got a message
{
strcat(errmsg,what);
//fprintf(stderr,"ERROR - In %s and error is %s\n",where ,what);
logp(3,errmsg);
}
else//we got nothing
{
strcat(errmsg,"No Message");
//fprintf(stderr,"ERROR - In %s\n",where);
logp(3,errmsg);
}
}
Initially everything work fine but when I trid to use any function which is defined in accessories.c compilation give me error.
For example I use the log function in sendfdsock.c :
#include "accessories.h"
#define CONTROLLEN CMSG_LEN(sizeof(int))
static struct cmsghdr *cmptr = NULL; /* malloc'ed first time */
int send_err(int fd, int errcode, const char *msg);
int send_fd(int fd, int fd_to_send);
int main(int argc, char const *argv[])
{
logp(1,"started"); //This function is defined in accessories.c
int fd_to_send;
if((fd_to_send = open("vi",O_RDONLY)) < 0)
printf("vi open failed");
struct sockaddr_un address;
int socket_fd, nbytes;
char buffer[256];
........
Output of the compilation is:
abhi#abhi-me:~/bridge/server$ make compileAll
gcc -c sendfdsock.c
sendfdsock.c: In function ‘send_fd’:
sendfdsock.c:111:9: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘ssize_t’ [-Wformat]
sendfdsock.c:114:5: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘ssize_t’ [-Wformat]
gcc -o sendfdsock sendfdsock.o
sendfdsock.o: In function `main':
sendfdsock.c:(.text+0x32): undefined reference to `logp'
collect2: ld returned 1 exit status
make: *** [sendfdsock] Error 1
abhi#abhi-me:~/bridge/server$
Why undefined reference to logp error?
Why I don't write accessories.o in final linking:
But as this example is given in GNU Make Doc:
In this example, all the C files include ‘defs.h’, but
only those defining editing comminclude ‘command.h’, and only
low level files that change the editor buffer include 'buffer.h':
edit : main.o kbd.o command.o display.o \
insert.o search.o files.o utils.o
cc -o edit main.o kbd.o command.o display.o \
insert.o search.o files.o utils.o
main.o : main.c defs.h
cc -c main.c
kbd.o : kbd.c defs.h command.h
cc -c kbd.c
command.o : command.c defs.h command.h
cc -c command.c
display.o : display.c defs.h buffer.h
cc -c display.c
insert.o : insert.c defs.h buffer.h
cc -c insert.c
search.o : search.c defs.h buffer.h
cc -c search.c
files.o : files.c defs.h buffer.h command.h
cc -c files.c
utils.o : utils.c defs.h
cc -c utils.c
clean :
rm edit main.o kbd.o command.o display.o \
insert.o search.o files.o utils.o
Here while linking all the files in edit they don't write defs.o or buffer.o. Means while linking they are not including object files of header files. Also they have not written any target like: defs.o or buffer.o
Why?
You just missed accessories.o in both linking targets. Something like this:
accessories.o: accessories.c
sendfdsock: sendfdsock.o accessories.o
$(CC) -o $# $(CFLAGS) $(LDFLAGS) $+
Also, consider using the built-in rules, just modify their parameters, if needed. See make -p for the full list (and makes infopage)
You misunderstand the relationship between source files, header files and object files.
Suppose I have the following four files:
//foo.h
#define PI 3.1
//bar.h
void func();
//bar.c
#include "foo.h"
#include "bar.h"
void func()
{
...
}
//baz.c
#include "foo.h"
#include "bar.h"
int main()
{
func();
}
(I left out the header guards, I presume you know about those.) I must use the compiler to produce an object file from each source file: bar.c -> bar.o and baz.c -> baz.o. I don't have to make object files from the headers foo.h and bar.h, those will simply be #included by any source file that needs them. Then I link the object files together to form an executable:
baz: bar.o baz.o
gcc -o baz bar.o baz.o
bar.o: bar.c foo.h bar.h
gcc -c bar.c
baz.o: baz.c foo.h bar.h
gcc -c baz.c
If I neglect to link bar.o into the executable, I'll get a linker error when the linker gets to the place where baz calls func() and the linker doesn't know what to put there (because it lacks the definition of func() in bar.o):
baz.o: In function `main':
baz.c:(.text+0x32): undefined reference to `func()'
So the GNU Make doc is correct, and as Alex said, your rule should have:
sendfdsock:sendfdsock.o accessories.o
...
accessories.o: accessories.c accessories.h
...
(Incidentally, once you get this makefile working, we can show you how to make it more concise.)
I'm trying to reproduce an example from Network Security with OpenSSL (by Chandra et al). The program consists of client.c server.c common.h and common.c. client.c simply creates a connection to the server on port 6012 and reads data from stdin and then send those data to the server. The server.c reads data from socket and writes it back out to stdout.
The problem is that server.c always get stuck in if(BIO_do_accept(acc) <= 0) at line 62 and never gets data sent from client.c, which runs perfectly fine. I later found the problem is that pthread_create(...) at line 66 ( which is defined as THREAD_CREATE(...) in common.h) failed and it returned 4294967295. Because THREAD_CREATE(...) failed, the program never get a chance to run do_server_loop in server_thread(...), which explains why the server never got the data from client.
How should I interpret the return values from pthread_create and how should I fix it?
PS. I later used strerror to convert 4294967295 and it returned "Unknown error".
Any help will be much appreciated!
//////////////////////////////////////////////////
Here is server.c:
#include "common.h"
void do_server_loop(BIO *conn)
{
int err, nread;
char buf[80];
do
{
fprintf(stderr, "server_loop executed.\n");
for(nread = 0; nread < sizeof(buf); nread += err)
{
err = BIO_read(conn, buf + nread, sizeof(buf) - nread);
if(err <= 0){
break;
}
}
fwrite(buf, 1, nread, stdout);
}
while (err > 0);
}
void THREAD_CC server_thread(void *arg)
{
fprintf(stderr, "server_thread(void *arg) executed.\n");
BIO *client = (BIO *)arg;
#ifndef WIN32
pthread_detach(pthread_self());
#endif
fprintf(stderr, "Connection opened.\n");
do_server_loop(client);
fprintf(stderr, "Connection closed.\n");
BIO_free(client);
ERR_remove_state(0);
#ifdef WIN32
_endthread();
#else
return 0;
#endif
}
int main(int argc, char *argv[])
{
BIO *acc, *client;
int thread_create_result;
THREAD_TYPE tid;
init_OpenSSL();
acc = BIO_new_accept(PORT);
if(!acc){
int_error("Error creating server socket");
}
if(BIO_do_accept(acc) <= 0){
int_error("Error binding server socket");
}
for(;;)
{
if(BIO_do_accept(acc) <= 0){
int_error("Error accepting connection");
}
client = BIO_pop(acc);
thread_create_result = THREAD_CREATE(tid, server_thread, client);
if(thread_create_result != 0){
fprintf(stderr, "THREAD_CREATE failed! returns: %s.\n", \
strerror(thread_create_result));
fprintf(stderr, "thread_create_result has the value: %u.\n", \
thread_create_result);
exit(-1);
}
}
BIO_free(acc);
return 0;
}
Here is common.h
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <openssl/bio.h>
#include <openssl/err.h>
#include <openssl/hmac.h>
#include <openssl/objects.h>
#include <openssl/rand.h>
#include <openssl/ssl.h>
#include <openssl/x509.h>
#include <openssl/x509v3.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
#ifndef WIN32
#include <pthread.h>
#define THREAD_CC *
#define THREAD_TYPE pthread_t
#define THREAD_CREATE(tid, entry, arg) pthread_create(&(tid), NULL, \
(entry), (arg))
#else
#include <windows.h>
#include <process.h>
#define THREAD_CC __cdecl
#define THREAD_TYPE DWORD
#define THREAD_CREATE(tid, entry, arg) do { _beginthread((entry), 0, (arg));\
(tid) = GetCurrentThreadId();\
} while (0)
#endif
#define PORT "6012" //port
#define SERVER "10.1.251.24" //server address
#define CLIENT "10.1.21.46" //client address
#define int_error(msg) handle_error(__FILE__, __LINE__, msg)
void handle_error(const char *file, int lineno, const char *msg);
void init_OpenSSL(void);
Makefile:
CC = gcc
OPENSSLDIR = /usr/local/ssl
#CFLAGS = -g -Wall -W -I${OPENSSLDIR}/include -O2 -D_REENTRANT -D__EXTENSIONS__
CFLAGS = -g -Wall -W -I${OPENSSLDIR}/include -O2
RPATH = -R${OPENSSLDIR}/lib
#LD = ${RPATH} -L${OPENSSLDIR}/lib -lssl -lcrypto -lsocket -lnsl -lpthread
LD = -L${OPENSSLDIR}/lib -lssl -lcrypto -lsocket -lnsl -pthread
OBJS = common.o
PROGS = server
all: ${PROGS}
server: server.o ${OBJS}
${CC} server.o ${OBJS} -o server ${LD}
clean:;
${RM} ${PROGS} *.ln *.BAK *.bak *.o
Change
if(thread_create_result = !0){
to
if(thread_create_result != 0){
Besides, you can use strerror function to convert error code to human-readable form.
add -D_REENTRANT on compile command lines and -lpthread on the link command line.
-D_REENTRANT will tell C/C++ libraries that your program is in multithread mode and -lpthread just load the shared library libpthread.so at runtime. I found this at William Garrison's POSIX threads tutorial and this link.
Here is the Makefile:
CC = gcc
OPENSSLDIR = /usr/local/ssl
CFLAGS = -g -Wall -W -I${OPENSSLDIR}/include -O2 -D_REENTRANT -D__EXTENSIONS__
RPATH = -R${OPENSSLDIR}/lib
LD = ${RPATH} -L${OPENSSLDIR}/lib -lssl -lcrypto -lsocket -lnsl -lpthread
OBJS = common.o
PROGS = server
all: ${PROGS}
server: server.o ${OBJS}
${CC} server.o ${OBJS} -o server ${LD}
clean:;
${RM} ${PROGS} *.ln *.BAK *.bak *.o