DLL Programmer's Guide for TNS/R Systems

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Finding Symbol Definitions

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

4-7

The SearchList for a Localized Loadfile

The final searchList is shown at the bottom of Figure 4-4. This shows how to develop a

localized searchList for Program when A re-exports D and no other DLLs re-export.

The arrows point to the referenced libraries in the algorithm after the indicated loop

run.

Program will use C’s definition of xray, since C precedes D in the searchList. But,

assuming D is localized, D will use its own definition of xray.

If we change the conditions so that B re-exports F, then Program’s searchList becomes

Program, UL, A, B, C, D, F. If now D re-exports G, then Program’s searchList becomes

Program, UL, A, B, C, D, F, G. Then if User Library re-exports H, the searchList

becomes Program, UL, A, B, C, H, D, F, G. If E re-exports G, this has no effect on the

searchList, because E itself is not re-exported; hence, E does not appear on the

searchList.

Localized import gives the programmer tight control over how imported symbols are

resolved. It is consistent with previous conventions used on HP NonStop systems;

SRLs are inherently localized. Localized import facilitates (future) load-time

optimizations, because the linker's search list is the same as the loader's. Finally,

localized import will be necessary for security in future when PIC programs and DLLs

support license and privilege.

Figure 4-3. The Loadfiles of Figure 1-5, Now Showing the Use and Availability of

the Global Symbol xray.

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

VST042.vsd

User Library

(DLL)

Lib H

Imports xray

Exports xray