HP-UX Reference (11i v1 00/12) - 5 Miscellaneous Topics, 7 Device (Special) Files, 9 General Information, Index (vol 9)

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dld.sl(5) dld.sl(5)

dependents, et cetera.

Binding

The dynamic loader also resolves symbolic references between the executable and libraries. By default,

function calls are trapped via the linkage table and bound on ﬁrst reference. References to data symbols

and other absolute address references cannot be trapped. They are bound on the ﬁrst resolution of a func-

tion call that could potentially reference the object.

If the -B immediate option to ld is used, the loader binds all necessary references at startup time.

This increases the startup cost of a program, but ensures that no more binding operations will be required

later. Thus, better real-time response may result, and the risk of a later abort due to unresolved externals

is eliminated.

The fastbind tool can be used to improve the start-up time of programs that use shared libraries

(incomplete executables). The fastbind tool performs analysis on the shared library routines and data

used to bind the symbols and stores this information in the executable ﬁle. The dynamic loader will notice

that this information is available, and it will use this fastbind information to bind the symbols instead of the

standard search method. For more details refer to fastbind(1) and the +help option to ld(1) or the HP-UX

Linker and Libraries User’s Guide manual.

Breadth-ﬁrst Searching

This is only availableon PA64. By default, the dynamic loader will do breadth-ﬁrst searching when binding

symbols. If the incomplete executable was linked with

+compat or if a shl_load() is being executed,

then depth-ﬁrst searching is used. Breadth-ﬁrst searching speciﬁes that the dynamic loader will look for

symbols starting with the incomplete executable followed by all loaded shared libraries in a left to right

order until the symbol is found. For example, the incomplete executable is searched followed by all

libraries in its library load list. Then the dependent shared libraries of the ﬁrst library in the library load

list list is searched, followed by the dependent shared libraries of the second library in the list, et cetera.

Depth-ﬁrst Searching

This is the only search behavior on PA32 and is used on PA64 if doing a

shl_load() or if the incomplete

executable was linked with

+compat. The dynamic loader will search the incomplete executable followed

by the ﬁrst library in its library load list. The ﬁrst dependent library of this library is then searched, fol-

lowed by the ﬁrst dependent of this dependent, and so on. When there are no more dependents, the

siblings and their dependents are searched until eventually the second library in the program’s library load

list is searched, followed by the ﬁrst dependent of this library, et cetera.

Version Control

Since code from a shared library is mapped at run time from a separate shared library ﬁle, modiﬁcations to

a shared library may alter the behavior of existing executables. In some cases, this may cause programs to

operate incorrectly. Two means of version control is provided to solve this problem.

Intra-Library Versioning

This is available on PA32 only. Whenever an incompatible change is made to a library interface, both ver-

sions of the affected module or modules are included in the library. A mark indicating the date

(month/year) the change was made is recorded in the new module via the pragma HP_SHLIB_VERSION

in C, or the compiler directive SHLIB_VERSION

in Fortran and Pascal. This date applies to all symbols

deﬁned within the module. A high water mark giving the date of the latest incompatible change is recorded

in the shared library, and the high water mark for each library linked with the program is recorded in the

incomplete executable ﬁle. At run time, the dynamic loader checks the high water mark of each library and

loads the library only if it is at least as new as the high water mark recorded at link time. When binding

symbolic references, the loader chooses the latest version of a symbol that is not later than the high water

mark recorded at link time. These two checks help ensure that the version of each library interface used at

run time is the same as was expected at link time. Intra-library versioning may be removed in a future

release.

Library-level Versioning

The second way for users to version their libraries is by using a new naming convention, libname.n where

n is a numeral that is incremented with every new release of the library. When using the new naming

scheme, users must specify an internal name for the shared library by using the

+h internal_name

option to ld when building the shared library. This internal name is recorded in each incomplete execut-

able or shared library that links with the shared library.

HP-UX Release 11i: December 2000 − 3 − Section 5−−43

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