DLL Programmer's Guide for TNS/E Systems

DLLs on a TNS/E System

DLL Programmer’s Guide for TNS/E Systems—527252-006

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You invoke the linker by a single command, eld, and control it by items you enter in its

command stream, which comprises the options, file names, and parameters that

modify the eld command.

Later, the loader brings together programs with their required libraries in structures like

that shown in Figure 1-2 on page 1-4. To enable the linker to find the required libraries

when it links a loadfile, the loadfile’s programmer must enter in the command stream

the names of libraries that can provide symbols that this loadfile needs. From these

names, the linker creates in the loadfile a libList, which lists the names and certain

attributes of each of these libraries. A library that is listed in a loadfile’s libList is said to

be directly referenced by that loadfile.

In simple compile-and-link operations, the compiler runs the linker automatically. When

it does this, the compiler tells the linker the names of certain standard libraries. If those

are the only libraries required, you need do nothing more. But if you require other

libraries, you can command the compiler to pass them to the linker, or, you can run the

linker yourself. In the latter case you must provide to the linker with the required library

names, including the ones the compiler would have automatically done for you.

The linker can run on a TNS/E machine in either the Guardian or OSS environment.

It can also run on Win32 support machines, usually in an ETK environment. In this

document, these support machines are called auxiliary systems. The object file

produced can only be run on TNS/E systems.

Once a program and its DLLs have been processed by the PIC linker, they can be

loaded for execution by a special library program (the run-time linker rld) that works

with the operating system. This combined facility of rld and the operating system that

loads programs and libraries into virtual memory for execution is called, in this

document, the loader.

FastLoad

Required libraries are not statically linked with the program. Instead, at load time, the

program and its DLLs are brought into virtual memory, and the loader resolves

references among them. The loader does not alter the stored file image of the loadfile;

rather, it changes only the loaded memory image of the loadfile’s tables and other

initialized data. So this load-time adjustment might be repeated every time a program

and its DLLs are loaded, although the FastLoad facility loads a preset loadfile without

having to rebind it.

Automatic Update

If rld has to rebind a loadfile and the loadfile import control is localized, it will update

the preset bindings in the loadfile with the cooperation of the NonStop operating

system. This is called automatic update. rld and the operating system only

automatically update loadfiles at process creation time. If a loadfile is loaded via a call

to dlopen(), the loadfile is not automatically updated.