I am attempting to build a (very simple) Python extension from C code and have run into a snag in the compilation.
(For the record: my C skills are very out-of-date and my code is probably awful.)
As directed in the docs and on another site I found, I created a C file that exposes the functionality I need built into a Python module:
#include "strcrypto.h"
#include <stdlib.h>
#define CRYPTO_POOLNUMBER 15
int main() {
return 0;
}
char* encryptString(char* string) {
COMM* comm;
char* encrypted_string = malloc(sizeof(char) * 4096);
int res;
comm = init_client(CRYPTO_PORT);
if (comm == NULL) {
return NULL;
}
res = StrEncrypt(comm, string, encrypted_string, CRYPTO_POOLNUMBER);
end_client(comm);
if (res != 1) {
return NULL;
}
else {
return encrypted_string;
}
}
char* decrypt(char* string) {
COMM* comm;
char* decrypted_string = malloc(sizeof(char) * 4096);
int res;
comm = init_client(CRYPTO_PORT);
if (comm == NULL) {
return NULL;
}
res = StrDecrypt(comm, string, decrypted_string);
end_client(comm);
if (res != 1) {
return NULL;
}
else {
return decrypted_string;
}
}
char* randomToken(char* string) {
COMM* comm;
char* token = malloc(sizeof(char) * 4096);
int res;
comm = init_client(CRYPTO_PORT);
if (comm == NULL) {
return NULL;
}
res = getPBToken(comm, string, token);
end_client(comm);
if (res != 1) {
return NULL;
}
else {
return token;
}
}
char* fixedToken(char* string) {
COMM* comm;
char* token = malloc(sizeof(char) * 4096);
int res;
comm = init_client(CRYPTO_PORT);
if (comm == NULL) {
return NULL;
}
res = getFixedToken(comm, string, token);
end_client(comm);
if (res != 1) {
return NULL;
}
else {
return token;
}
}
I also created the C file that wraps the methods for Python:
#include <Python.h>
static PyObject* crypto_encrypt(PyObject* self, PyObject* args) {
char* original_string;
char* encrypted_string;
PyObject* return_value;
if (!PyArg_ParseTuple(args, "s", &original_string)) {
return NULL; // Could not parse string or no string was passed.
}
encrypted_string = encryptString(original_string);
if (encrypted_string == NULL) {
return NULL;
}
else {
return_value = PyString_FromString(encrypted_string);
free(encrypted_string);
return return_value;
}
}
static PyObject* crypto_decrypt(PyObject* self, PyObject* args) {
char* original_string;
char* decrypted_string;
PyObject* return_value;
if (!PyArg_ParseTuple(args, "s", &original_string)) {
return NULL; // Could not parse string or no string was passed.
}
decrypted_string = decryptString(original_string);
if (decrypted_string == NULL) {
return NULL;
}
else {
return_value = PyString_FromString(decrypted_string);
free(decrypted_string);
return return_value;
}
}
static PyObject* crypto_fixedToken(PyObject* self, PyObject* args) {
char* original_string;
char* token;
PyObject* return_value;
if (!PyArg_ParseTuple(args, "s", &original_string)) {
return NULL; // Could not parse string or no string was passed.
}
token = fixedToken(original_string);
if (token == NULL) {
return NULL;
}
else {
return_value = PyString_FromString(token);
free(token);
return return_value;
}
}
static PyObject* crypto_randomToken(PyObject* self, PyObject* args) {
char* original_string;
char* token;
PyObject* return_value;
if (!PyArg_ParseTuple(args, "s", &original_string)) {
return NULL; // Could not parse string or no string was passed.
}
token = randomToken(original_string);
if (token == NULL) {
return NULL;
}
else {
return_value = PyString_FromString(token);
free(token);
return return_value;
}
}
static PyMethodDef CryptoMethods[] = {
{ "encrypt", crypto_encrypt, METH_VARARGS, "Encrypt text using a Crypto server." },
{ "decrypt", crypto_decrypt, METH_VARARGS, "Decrypt text encrypted using a Crypto server." },
{ "getFixedToken", crypto_fixedToken, METH_VARARGS, "Return a fixed PKCS5 token from Crypto." },
{ "getRandomToken", crypto_randomToken, METH_VARARGS, "Return a random PKCS5 token from Crypto." },
{ NULL, NULL, 0, NULL }
};
PyMODINIT_FUNC initcrypto(void) {
(void) Py_InitModule("crypto", CryptoMethods);
}
Finally, I created a setup.py file that creates the extension and calls setup() on the extension:
from distutils.core import setup, Extension
ext = Extension("crypto",
["cryptomodule.c", "crypto.c"],
libraries = ["strcrypto",],
library_dirs = ["/usr/local/lib",]
)
setup(name = "crypto", ext_modules = [ext,])
The library "strcrypto" is actually "libstrcrypto.a" and was provided to me; it wasn't something I wrote. Unfortunately, that is also what appears to be causing the error when I go to install the file:
running install
running build
running build_ext
building 'crypto' extension
x86_64-linux-gnu-gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.7 -c cryptomodule.c -o build/temp.linux-x86_64-2.7/cryptomodule.o
cryptomodule.c: In function ‘crypto_encrypt’:
cryptomodule.c:15:5: warning: implicit declaration of function ‘encryptString’ [-Wimplicit-function-declaration]
encrypted_string = encryptString(original_string);
^
cryptomodule.c:15:22: warning: assignment makes pointer from integer without a cast [enabled by default]
encrypted_string = encryptString(original_string);
^
cryptomodule.c: In function ‘crypto_decrypt’:
cryptomodule.c:36:5: warning: implicit declaration of function ‘decryptString’ [-Wimplicit-function-declaration]
decrypted_string = decryptString(original_string);
^
cryptomodule.c:36:22: warning: assignment makes pointer from integer without a cast [enabled by default]
decrypted_string = decryptString(original_string);
^
cryptomodule.c: In function ‘crypto_fixedToken’:
cryptomodule.c:57:5: warning: implicit declaration of function ‘fixedToken’ [-Wimplicit-function-declaration]
token = fixedToken(original_string);
^
cryptomodule.c:57:11: warning: assignment makes pointer from integer without a cast [enabled by default]
token = fixedToken(original_string);
^
cryptomodule.c: In function ‘crypto_randomToken’:
cryptomodule.c:78:5: warning: implicit declaration of function ‘randomToken’ [-Wimplicit-function-declaration]
token = randomToken(original_string);
^
cryptomodule.c:78:11: warning: assignment makes pointer from integer without a cast [enabled by default]
token = randomToken(original_string);
^
x86_64-linux-gnu-gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.7 -c crypto.c -o build/temp.linux-x86_64-2.7/crypto.o
crypto.c:6:5: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
int main() {
^
x86_64-linux-gnu-gcc -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-Bsymbolic-functions -Wl,-z,relro -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -D_FORTIFY_SOURCE=2 -g -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security build/temp.linux-x86_64-2.7/cryptomodule.o build/temp.linux-x86_64-2.7/crypto.o -L/usr/local/lib -lstrcrypto -o build/lib.linux-x86_64-2.7/crypto.so
/usr/bin/ld: /usr/local/lib/libstrcrypto.a(strcrypto.o): relocation R_X86_64_32 against `.rodata.str1.1' can not be used when making a shared object; recompile with -fPIC
/usr/local/lib/libstrcrypto.a: error adding symbols: Bad value
collect2: error: ld returned 1 exit status
error: command 'x86_64-linux-gnu-gcc' failed with exit status 1
I don't know what that error means, because as you can see, the gcc calls are indeed using -fPIC.
Can someone please point out what I'm doing wrong here? Thanks in advance.
The Python extension you are building is a shared library. The code in a shared library
must be compiled to be position independent. This is done by compiling with -fPIC.
Your problem is that your libstrcrypto.a is not compiled with -fPIC and therefore cannot be used inside a shared library. You have several alternatives:
libstrcrypto.a that is compiled with -fPIC.libstrcrypto.a.