DLL Programmer's Guide for TNS/E Systems

Essential DLL Facility Controls
DLL Programmer’s Guide for TNS/E Systems—527252-006
2-19
Unresolved Symbols at Load Time
The -RLD_first_L option is rarely necessary, because the public libraries have
unique names that should not overlap those supplied by the user or other agencies.
It is more efficient to have the public libraries first on the path search list at load time,
because the set of public libraries can be searched very quickly using a table in
memory.
Unresolved Symbols at Load Time
The loader always searches for every symbol definition that your loadfile must import.
Until it finds a library that offers a symbol definition that your loadfile needs, it considers
that symbol unresolved.
The loader’s search path can be as described under The Link-Time-Defined Search
Path of the Loader on page 2-17, but it might be more extensive, as described in
Finding Symbol Definitions on page 4-1. After looking in all the files specified for this
search and in the implicit system and millicode libraries, if the loader cannot resolve a
symbol reference, it will likely deem this an error; see the definition of set
RLD_unresolved under How to Set Run-Time Attributes of Your Loadfile on
page 5-6.
Also, you may want the linker to help you to find unresolved symbols prior to load time.
For this, see Making the Linker Look for Unresolved Symbols on page 5-3.
Simultaneously Using Different Versions of a DLL
By controlling the loader’s search path, you can allow two different versions of the
same DLL with the same name to be loaded and run in two different processes
simultaneously. This can be useful when testing a new version of a DLL with existing
application code that you do not want to modify. One way to substitute a test DLL for a
production DLL is to link the program and DLLs to allow load-time search-path
specifications, as described in Controlling the Loader’s Search Path at Load Time on
page 5-13.
Default Setting and Checking of File Attributes
The linker sets certain attributes of the loadfile being linked and performs certain
consistency checks. This subsection discusses those that you must know about. How
to set these and others to non-default values is covered in How to Set Run-Time
Attributes of Your Loadfile on page 5-6.
Floating-Point Type
Setting the Floating-Point Type of a Loadfile Being Linked
The floating-point type attribute of the loadfile being linked is determined in one of two
ways.