I have a problem with using libnetlink.
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <libnetlink.h>
int main(int argc, char **argv)
{
struct rtnl_handle* rth;
unsigned bitmap_socket_group;
if ((rtnl_open(rth,bitmap_socket_group))==-1)
{
printf("Some sht happend\n");
return -1;
}
return 0;
}
After that i'm running gcc -o rt route-test.c and it returns:
/tmp/ccvqPhGI.o: In function `main': route-test.c:(.text+0x19): undefined reference to `rtnl_open'
collect2: error: ld returned 1 exit status
All i want is just to test libnetlink. As a helloworld.
Is it a problem with gcc arguments?
Hope for help:)
It appears you are either missing a header or your a failing to link against a needed library. Are you sure there is no -lnetlink you need to include in your compile string?
– David C. Rankin
You're right, i need -lnetlink! Thank you:)
– AlexZ
According to the documentation, you may need to include more librairies :
#include <asm/types.h>
#include <libnetlink.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
Related
I'm trying to use the memfd_create syscall in my C code. I tried to include sys/memfd.h as the man page for memfd_create says is appropriate, but GCC gives me an error "sys/memfd: No such file or directory".
I've tried Googling around and couldn't find anyone having the same problem. I noticed some versions of the manpage for memfd_create say that I should include sys/mman.h, but it didn't seem to help when I tried it. It would say memfd_create was implicitly declared.
Here is a minimal reproduction of my problem.
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/memfd.h>
int main(){
int fd;
fd = memfd_create("test", MFD_CLOEXEC);
return 0;
}
I expect the above code to compile and run without error.
On older systems, you'll have to include linux/memfd.h for the MFD_ defines, and call memfd_create() via the the syscall(2) wrapper (and include unistd.h and sys/syscall.h for it work).
#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/memfd.h>
#include <err.h>
int main(void){
int fd;
if((fd = syscall(SYS_memfd_create, "test", MFD_CLOEXEC)) == -1)
err(1, "memfd_create");
return 0;
}
The Ubuntu man-pages in Bionic (18.04) are not up to date with this API (including its implementation in Bionic).
The Focal man-page correctly shows how to include memfd_create(). It says:
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <sys/mman.h>
So you only need to include <sys/mman.h>, and you need to build with -D_GNU_SOURCE in your compiler flags. Or, do as the man page says and literally #define _GNU_SOURCE before including the header. However, I recommend just compiling with -D_GNU_SOURCE instead.
I am having a hard time finding this missing reference when running : gcc server.c -I /pwdmanlib/src -lssl -lcrypto -o server the include is my src files (headers needs etc..) and the rest is th required ssl libraries.
I am getting the following output from gcc:
In file included from server.h:49:0,
from server.c:39:
/pwdmanlib/src/util/constants.h:30:0: warning: "LINE_MAX" redefined
#define LINE_MAX 2048
^
In file included from /usr/include/limits.h:147:0,
from /usr/lib/gcc/x86_64-linux-gnu/5/include-fixed/limits.h:168,
from /usr/lib/gcc/x86_64-linux-gnu/5/include-fixed/syslimits.h:7,
from /usr/lib/gcc/x86_64-linux-gnu/5/include-fixed/limits.h:34,
from /pwdmanlib/src/util/constants.h:26,
from server.h:49,
from server.c:39:
/usr/include/x86_64-linux-gnu/bits/posix2_lim.h:81:0: note: this is the location of the previous definition
#define LINE_MAX _POSIX2_LINE_MAX
^
In file included from server.c:39:0:
server.h: In function ‘start_server’:
server.h:126:34: warning: comparison between pointer and integer
if (p == NULL || listen_sock == NULL) {
^
In file included from server.c:39:0:
server.h: In function ‘routeClient’:
server.h:394:29: warning: passing argument 1 of ‘sendall’ makes pointer from integer without a cast [-Wint-conversion]
if (sendall(worker_sock, resp_data, fileLen) == -1) {
^
In file included from server.c:39:0:
server.h:70:5: note: expected ‘SSL * {aka struct ssl_st *}’ but argument is of type ‘int’
int sendall(SSL *ssl, char *buf, ssize_t *len);
^
/tmp/ccubinQD.o: In function `InitSSL':
server.c:(.text+0x1305): undefined reference to `OPENSSL_init_ssl'
server.c:(.text+0x1314): undefined reference to `OPENSSL_init_ssl'
server.c:(.text+0x1323): undefined reference to `OPENSSL_init_crypto'
/tmp/ccubinQD.o: In function `InitCTX':
server.c:(.text+0x1333): undefined reference to `TLS_server_method'
server.c:(.text+0x1350): undefined reference to `SSL_CTX_set_options'
collect2: error: ld returned 1 exit status
I found the OPENSSL_init_ssl function call in the ssl library and it is apparently getting included but can't be found by other references to it in the library?? The includes from my program are specified below:
ssl_funcs.h
#include <openssl/bio.h>
#include <openssl/ssl.h>
#include <openssl/err.h>
#include <openssl/crypto.h>
server.h
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <unistd.h>
#include "util/oop.h"
#include "util/stringops.h"
#include "util/constants.h"
#include "fawkes_proto.h"
#include "crypto/ssl_funcs.h"
server.c
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <unistd.h>
#include "server.h"
#include "util/constants.h"
When linking in dynamic libraries with the -l option, these must occur last, after all other options:
gcc server.c -I /pwdmanlib/src -o server -lssl -lcrypto
Besides this, you should address the warnings in your code. These can potentially lead to undefined behavior.
To add to dbush's answer above I also needed to compile with an explicit target directory for the linking library like so: gcc server.c -I/pwdmanlib/src -o server -L/usr/local/lib -lssl -lcrypto
Moreover, I also implemented a solution for this in CMake (build system I use for my projects) and provided that below as well in case anyway else might find that useful. This is just the pertinent portion of it, if anyone wants the full src to the cmake I would be more than happy to provide it.
CMakeLists.txt
# Add libraries
include_directories(${LOCAL_LIBS_DIR})
include_directories("/usr/local/lib")
#link_directories("/usr/local/lib")
add_library(ssl SHARED IMPORTED) # or STATIC instead of SHARED
set_property(TARGET ssl PROPERTY IMPORTED_LOCATION "/usr/local/lib/libssl.so")
add_library(crypto SHARED IMPORTED) # or STATIC instead of SHARED
set_property(TARGET crypto PROPERTY IMPORTED_LOCATION "/usr/local/lib/libcrypto.so")
#include_directories("/opt/openssl-1.1.0e")
#find_package (my_library COMPONENTS REQUIRED component1 component2 OPTIONAL_COMPONENTS opt_component)
# Define build targets and link libraries
add_executable(main ${SOURCE_FILES})
target_include_directories(main PUBLIC /usr/include/openssl)
target_link_libraries(main
PRIVATE ${Boost_LIBRARIES}
PRIVATE ${PostgreSQL_LIBRARIES}
PRIVATE ${cJSON_ROOT_DIR}
# PRIVATE ${CryptoPP_ROOT_DIR}
# PRIVATE ${Kore_ROOT_DIR}
# PRIVATE ${POCO_LIBRARIES}
PRIVATE ssl
PRIVATE crypto
)
Here's my code:
#include <sys/types.h>
#include <stdio.h>
#include <dirent.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>
#include <sys/time.h>
#include <assert.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
int main(int argc, char** argv) {
sigignore(SIGTERM);
return 0;
}
Why do I get the following warning and how could I remove it?
implicit declaration of function ‘sigignore’
[-Wimplicit-function-declaration] sigignore(SIGTERM);
The program must be compiled like this: gcc -o foo.o foo.c.
Thanks
Man sigignore tells you to use #define _XOPEN_SOURCE 500 to enable sigignore. More on X/Open can be found here
The function you want to call has been marked as obsolete 15 years ago. The normal way to discourage people from using those functions (without actually breaking programs) is to have the implementation of the function left in the standard library, but remove the declaration from header files (or at least make it hard to enable).
Use sigaction or sigprocmask (depending on what you actually want to accomplish).
Given this code :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/shm.h>
#include <semaphore.h>
#include <pthread.h>
#define BUF_SIZE 256
int main()
{
key_t key;
char *virtualaddr;
sem_t *get, *put;
int shmid;
const char* messageOne = "Hello world , I'm child number 1\n";
const char* messageTwo = "Hello world , I'm child number 2\n";
char buf[BUF_SIZE];
key = ftok("anyfile",'R');
shmid = shmget(key,1024,0644|IPC_CREAT);
...
...
shmctl (shmid, IPC_RMID, NULL);
exit(EXIT_SUCCESS);
}
I get from eclipse undefined reference to sem_open .
I've check with this post since this question is very similar to mine , but didn't understand exactly where is my mistake ,
Can you please explain where do I need to fix it / add another compilation command (if this is indeed the case) ?
Much appreciated
You need to include -lpthread when compiling. This is used by the linker, to link your binary against the library.
The other answers already cover how to do this on the command line.
To do this in Eclipse, you need to follow the directions here:
In the project properties, go to : C/C++ Build --> Settings. Then
"Tool Settings", select "Libraries" under "Linker". You can add all
your project libraries there (without the "-l"). Also in the lower
part, you can add custom path to search libraries
When linking, you have to add the flag -pthread or -lrt to the command line. It's right there in the manual page.
As it is written in the first answer in the question you linked, you nedd to compile it in this way:
gcc source.c -lpthread
-lrt or -pthread will do the same.
I got the following error on compiling a c code I wrote. I understand that the problem is in the header file. Can anyone please tell me which all header files are needed to define these functions.
sign.c: In function ‘main’:
sign.c:78: warning: assignment makes pointer from integer without a cast
/tmp/ccnsSeHy.o: In function `sign_data_evp':
sign.c:(.text+0x68): undefined reference to `check_ssl_rv'
sign.c:(.text+0xd5): undefined reference to `check_ssl_rv'
sign.c:(.text+0x13e): undefined reference to `check_ssl_rv'
/tmp/ccnsSeHy.o: In function `main':
sign.c:(.text+0x1ca): undefined reference to `initialize'
sign.c:(.text+0x1d6): undefined reference to `select_engine'
sign.c:(.text+0x20a): undefined reference to `sign_data'
sign.c:(.text+0x216): undefined reference to `clean_engine'
sign.c:(.text+0x21b): undefined reference to `clean_up'
collect2: ld returned 1 exit status
The header files that I have used so far is:
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <netdb.h>
#include <unistd.h>
#ifdef __VMS
#include <socket.h>
#include <inet.h>
#include <in.h>
#else
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#endif
#include <openssl/crypto.h>
#include <openssl/ssl.h>
#include <openssl/err.h>
Operating platform: Linux
Thanks in advance.
You understand it wrong. It does not complain about unknown function prototype, it complains during the linking. So you probably forgot to link with some library or some object file.
try with this
gcc sslprogname.c -o sslprogname -Wl,-Bstatic -lssl -Wl,-Bdynamic -lssl3 -lcrypto.It worked for me