Guardian Native C Library Calls Reference Manual (G06.28+, H06.05+)

dlopen(3) Guardian Native C Library Calls Reference Manual

For Guardian programs, the class MAP DEFINE =_RLDVERBOSE performs the equivalent

action. For example:

ADD DEFINE =_RLDVERBOSE, CLASS MAP, FILE #4

Disposing of Unresolved Symbols

Users can specify an option to the ld or eld linker to control disposition of unresolved symbols in

a loadﬁle. The option is stored in the loadﬁle and determines whether rld or dlopen() generates

warnings or errors when it encounters unresolved procedure references in the loadﬁle.

For unresolved data symbols, dlopen( ) always reports an error.

For unresolved procedure symbols, the options are:

• Report errors; this is the default option set by the ld or eld linker

• Report warnings to the home terminal for references to unresolved procedures, but report

no errors (if RTLD_VERBOSE(1) is used, no warnings are reported)

• Report no errors or warnings, despite references to unresolved procedures

If any procedure symbol is unresolved when a loadﬁle is loaded, that symbol is bound to a func-

tion named UNRESOLVED_PROCEDURE_CALLED_(). The system (implicit) library

includes a default internal implementation of UNRESOLVED_PROCEDURE_CALLED_();

when called, it generates a nondeferrable SIGILL signal. The run-time loader searches for

UNRESOLVED_PROCEDURE_CALLED_() using the import controls speciﬁed in the

loadﬁle, just as it searches for any other symbol; therefore, a user’sdeﬁnition for the function

takes precedence over the internal deﬁnition.

NOTES

The rld dynamic loader is an unprivileged interface; it cannot be invoked from a program or

DLL that is licensed or has callable functions, or from a program with a priv entry point. Process

creation fails if such a ﬁle refers to dlopen( ), dlsym( ), dlclose(), dlerror(),ordlresultcode().

Depending upon the circumstances, process-creation error/detail value combinations of 77,11 or

78,7 can result.

RETURN VALUES

Upon successful completion, the dlopen( ) function returns a library handle valid for use with

other DLL functions. This handle is an arbitrary token, not an address; it cannot be assigned to a

pointer and dereferenced.

dlopen() returns a 0 (zero) if the ﬁle designated by object_pathname:

• Could not be found

• Could not be opened for execution

• Is not a DLL or an unlicensed public SRL

or if an error occurred during the loading or adjustment of the ﬁle’s symbolic references. The

dlerror() or dlresultcode() function should be called immediately to determine the problem.

ERRORS

The dlopen() function does not set the errno variable. Error information is available through the

dlerror() or dlresultcode() function.

Unresolved symbols can cause dlopen( ) to generate warnings or errors, depending on the user-

speciﬁed option for treating unresolved symbols. Warnings and errors are reported to the home

terminal.

If the option saved in the object ﬁle speciﬁes that unresolved symbols generate errors, dlopen()

returns 0 (zero) without loading any libraries; otherwise, dlopen() returns a valid library handle.

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