dlsym.3c (2010 09)

dlsym(3C) dlsym(3C)

this "real"

malloc() could be another user-deﬁned interface that added its own value and then used

RTLD_NEXT to ﬁnd the system malloc()

EXAMPLES

The following example shows how you can use

dlopen() and dlsym() to access either function or data

objects. For simplicity, error checking has been omitted.

void *handle;

int i, *iptr;

int (*fptr)(int);

/* open the needed object */

handle = dlopen("/usr/mydir/mylib.sl", RTLD_LAZY);

/* find address of function and data objects */

fptr = (int (*)(int))dlsym(handle, "some_function");

iptr = (int *)dlsym(handle, "int_object");

/* invoke function, passing value of integer as a parameter */

i = (*fptr)(*iptr);

The next example shows how one can use

dlsym() with RTLD_NEXT to add functionality to an existing

interface. Again, error checking has been omitted.

extern void record_malloc(void *, size_t);

void *

malloc(size_t sz)

{

void *ptr;

void *(*real_malloc)(size_t);

real_malloc = (void * (*) (size_t))

dlsym(RTLD_NEXT, "malloc");

ptr = (*real_malloc)(sz);

record_malloc(ptr, sz);

return ptr;

}