So, I'm messing around with some interposing code on OSX (gcc 4.2.1) and I'm trying to get the following to work:
When I call ./login using the DYLD_INSERT_LIBRARIES=my.dylib, it should override the default login implementation and use my custom implementation. Granted this is a contrived example, but its just to help me understand the point.
My source:
cat libinterposers.c
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include "login.h"
typedef struct interpose_s
{
void *new_func;
void *orig_func;
} interpose_t;
int my_open(const char *, int, mode_t);
int my_close(int);
int my_login();
static const interpose_t interposers[] __attribute__ ((section("__DATA, __interpose"))) =
{
{ (void *)my_open, (void *)open },
{ (void *)my_close, (void *)close },
{ (void *)my_login, (void *)login },
};
int my_login()
{
printf("--> my_login()\n");
return 1;
}
int my_open(const char *path, int flags, mode_t mode)
{
int ret = open(path, flags, mode);
printf("--> %d = open(%s, %x, %x)\n", ret, path, flags, mode);
return ret;
}
int my_close(int d)
{
int ret = close(d);
printf("--> %d = close(%d)\n", ret, d);
return ret;
}
cat login.c
#include <stdio.h>
#include "login.h"
int login()
{
return -1;
}
int main()
{
if (login() == 1)
{
printf("login successful\n");
}
else
{
printf("login failed\n");
}
}
And finally, login.h
int login();
Now when I execute with something like "cat /dev/null" it works fine ...
DYLD_INSERT_LIBRARIES=/tmp/libinterposers.dylib cat /dev/null
--> 3 = open(/dev/null, 0, 0)
--> 0 = close(3
However, when I run with my ./login example
DYLD_INSERT_LIBRARIES=/tmp/libinterposers.dylib ./login
login failed
As you can see, it just prints login failed, my custom "my_login" function never runs ... any ideas? Thanks in advance!
