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#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <dlfcn.h>
/*
* This is a minimal implementation of the ELF dlopen, dlclose, dlsym
* and dlerror routines based on HP's shl_load, shl_unload and
* shl_findsym. */
/*
* Reference Counting.
*
* Empirically it looks like the HP routines do not mainain a
* reference count, so I maintain one here.
*/
typedef struct lib_entry {
shl_t handle;
int count;
struct lib_entry *next;
} *LibEntry;
#define lib_entry_handle(e) ((e)->handle)
#define lib_entry_count(e) ((e)->count)
#define lib_entry_next(e) ((e)->next)
#define set_lib_entry_handle(e,v) ((e)->handle = (v))
#define set_lib_entry_count(e,v) ((e)->count = (v))
#define set_lib_entry_next(e,v) ((e)->next = (v))
#define increment_lib_entry_count(e) ((e)->count++)
#define decrement_lib_entry_count(e) ((e)->count--)
static LibEntry Entries = NULL;
static LibEntry find_lib_entry(shl_t handle)
{
LibEntry entry;
for (entry = Entries; entry != NULL; entry = lib_entry_next(entry))
if (lib_entry_handle(entry) == handle)
return entry;
return NULL;
}
static LibEntry new_lib_entry(shl_t handle)
{
LibEntry entry;
if ((entry = (LibEntry) malloc(sizeof(struct lib_entry))) != NULL) {
set_lib_entry_handle(entry, handle);
set_lib_entry_count(entry, 1);
set_lib_entry_next(entry, Entries);
Entries = entry;
}
return entry;
}
static void free_lib_entry(LibEntry entry)
{
if (entry == Entries)
Entries = lib_entry_next(entry);
else {
LibEntry last, next;
for (last = Entries, next = lib_entry_next(last);
next != NULL;
last = next, next = lib_entry_next(last)) {
if (entry == next) {
set_lib_entry_next(last, lib_entry_next(entry));
break;
}
}
}
free(entry);
}
/*
* Error Handling.
*/
#define ERRBUFSIZE 1000
static char errbuf[ERRBUFSIZE];
static int dlerrno = 0;
char *dlerror(void)
{
return dlerrno ? errbuf : NULL;
}
/*
* Opening and Closing Liraries.
*/
void *dlopen(const char *fname, int mode)
{
shl_t handle;
LibEntry entry = NULL;
dlerrno = 0;
if (fname == NULL)
handle = PROG_HANDLE;
else {
handle = shl_load(fname, mode, 0L);
if (handle != NULL) {
if ((entry = find_lib_entry(handle)) == NULL) {
if ((entry = new_lib_entry(handle)) == NULL) {
shl_unload(handle);
handle = NULL;
}
}
else
increment_lib_entry_count(entry);
}
if (handle == NULL) {
char *errstr;
dlerrno = errno;
errstr = strerror(errno);
if (errno == NULL) errstr = "???";
sprintf(errbuf, "can't open %s: %s", fname, errstr);
}
}
#ifdef DEBUG
printf("opening library %s, handle = %x, count = %d\n",
fname, handle, entry ? lib_entry_count(entry) : -1);
if (dlerrno) printf("%s\n", dlerror());
#endif
return (void *) handle;
}
int dlclose(void *handle)
{
LibEntry entry;
#ifdef DEBUG
entry = find_lib_entry(handle);
printf("closing library handle = %x, count = %d\n",
handle, entry ? lib_entry_count(entry) : -1);
#endif
dlerrno = 0;
if ((shl_t) handle == PROG_HANDLE)
return 0; /* ignore attempts to close main program */
else {
if ((entry = find_lib_entry((shl_t) handle)) != NULL) {
decrement_lib_entry_count(entry);
if (lib_entry_count(entry) > 0)
return 0;
else {
/* unload once reference count reaches zero */
free_lib_entry(entry);
if (shl_unload((shl_t) handle) == 0)
return 0;
}
}
/* if you get to here, an error has occurred */
dlerrno = 1;
sprintf(errbuf, "attempt to close library failed");
#ifdef DEBUG
printf("%s\n", dlerror());
#endif
return -1;
}
}
/*
* Symbol Lookup.
*/
void *dlsym(void *handle, const char *name)
{
void *f;
shl_t myhandle;
dlerrno = 0;
myhandle = (handle == NULL) ? PROG_HANDLE : (shl_t) handle;
if (shl_findsym(&myhandle, name, TYPE_PROCEDURE, &f) != 0) {
dlerrno = 1;
sprintf(errbuf, "symbol %s not found", name);
f = NULL;
}
return(f);
}
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