DLL Programmer's Guide for TNS/R Systems

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DLLs on a TNS/R System

DLL Programmer’s Guide for TNS/R Systems—522203-002

1-8

Finding the Needed libraries

The system automatically arranges loadfiles in virtual memory so there is no address

overlap and interference.

Finding the Needed libraries

A loadfile must be loaded with all the libraries that it directly references, that is, the

libraries in its libList. However, loading only the directly referenced libraries might not

be enough, because some of these libraries might directly reference still other libraries.

Therefore these other libraries must also be loaded, and they might further require still

other libraries. Proceeding in this way can lead to an arbitrarily long succession of

required libraries, all of which must be loaded to run the given loadfile.

The loader generates a list of all the libraries that must be loaded in order to run a

given loadfile by starting from the libList of that loadfile and proceeding through the

libLists of all the required libraries. This generated list is that loadfile’s loadList, and

the loader orders it in the sequence that these libraries are to be loaded, as discussed

in The SearchList for a Globalized Loadfile on page 4-8. Subsequently, the loader uses

the loadList to effect the loading operation.

Among the libraries on its loadList, the loadfile directly references those libraries on its

own libList, while the rest are indirectly referenced libraries. Figure 1-4, below, shows a

more detailed view of what Figure 1-2 on page 1-4 suggests. Figure 1-4 illustrates how

the program directly references libraries A, B, and C, which were specified to the linker

by the programmer and consequently appear in Program’s libList. Also, A directly

references D and E; B directly references F; and C directly references F. The

programmers of A, B, and C stated these requirements for these libraries when each

was linked. Likewise, D and E both directly reference G. Finally, neither F nor G

reference any other libraries.

For the loadfiles in Figure 1-4:

Figure 1-4. Loadfiles and Their libLists (to create the structure in Figure 1-2)

Program

DLL A

DLL B

DLL C

DLL D

DLL E

Lib G

Lib F

Lib A

Lib B

Lib C

Lib F

Lib D

Lib E

Lib F

Lib G

Code

and

Data

libList

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