HP-UX Reference (11i v3 07/02) - 3 Library Functions A-M (vol 6)

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dlopen_pa(3C) dlopen_pa(3C)

(HP 9000 Systems Only)

#include <stdio.h>

#include <dl.h>

main(int argc, char **argv) {

char * str;

shl_t shl;

void (*fptr)(void);

char *strpath[267];

sprintf(strpath, %s%s", SHLIB_PATH= ,argv[1]);

putenv(strpath);

dld_getenv();

shl = shl_load( a.sl", BIND_IMMEDIATE | DYNAMIC_PATH, 0);

if(!shl) {

printf("shl_load failed\n");

exit(-1);

}}

If the value of ﬁle is 0

, dlopen() provides a handle on a "global symbol object". This object provides

access to the symbols from an ordered set of objects consisting of the original

a.out, all of the objects that

were loaded at program startup along with the

a.out, and all objects loaded using a

dlopen() opera-

tion along with the

RTLD_GLOBAL ﬂag. As the latter set of objects can change during execution, the set

identiﬁed by handle can also change dynamically.

Only a single copy of an object ﬁle is brought into the address space, even if

dlopen() is invoked multiple

times in reference to the ﬁle, and even if different path names are used to reference the ﬁle.

When a shared object is brought into the address space of a process, it may contain references to symbols

whose addresses are not known until the object is loaded. These references must be relocated before the

symbols can be accessed. The mode parameter governs when these relocations take place and may have

the following values:

RTLD_TEXT_PRIVATE

Under this mode, the shared library loaded has its text segment mapped private.

This can be useful for debugging.

RTLD_LAZY Under this mode, only references to data symbols are relocated when the object is

loaded. References to functions are not relocated until a given function is invoked for

the ﬁrst time. This mode should result in better performance, since a process may not

reference all of the functions in any given shared object.

RTLD_NOW Under this mode, all necessary relocations are performed when the object is ﬁrst

loaded. This may result in some wasted effort, if relocations are performed for func-

tions that are never referenced, but is useful for applications that need to know as

soon as an object is loaded that all symbols referenced during execution are available.

Any object loaded by dlopen() that requires relocations against global symbols can reference the symbols

in the original a.out, any objects loaded at program startup, from the object itself as well as any other

object included in the same dlopen() invocation, and any objects that were loaded in any dlopen()

invocation that speciﬁed the RTLD_GLOBAL ﬂag. To determine the scope of visibility for the symbols

loaded with a dlopen() invocation, the mode parameter should be bitwise or’ed with one of the following

values:

RTLD_GLOBAL The object’s symbols are made available for the relocation processing of any other

object. In addition, symbol lookup using dlopen(0,mode) and an associated

dlsym() allows objects loaded with RTLD_GLOBAL to be searched.

RTLD_LOCAL The object’s symbols are made available for relocation processing only to objects

loaded in the same dlopen() invocation.

If neither RTLD_GLOBAL nor RTLD_LOCAL are speciﬁed, the default is RTLD_LOCAL .

If a ﬁle is speciﬁed in multiple dlopen() invocations, mode is interpreted at each invocation. Note, how-

ever, that once RTLD_NOW has been speciﬁed, all relocations will have been completed, rendering any

further RTLD_NOW operations redundant and any further RTLD_LAZY operations irrelevant. Similarly

note that once RTLD_GLOBAL has been speciﬁed, the object will maintain the RTLD_GLOBAL status

regardless of any previous or future speciﬁcation of RTLD_LOCAL , so long as the object remains in the

address space (see dlclose(3C)).

312 Hewlett-Packard Company − 2 − HP-UX 11i Version 3: February 2007