Linker and Libraries Guide

Creating a Weak Version Definition

Internal changes to an object that do not require the introduction of a new interface definition can be defined by creating a weak version definition. Examples of such changes are bug fixes or performance improvements. Such a version definition is empty. The version definition has no global interface symbols associated with the definition.

For example, suppose the data file data.c, used in the previous examples, is updated to provide more detailed string definitions.

$ cat data.c
const char * _foo1 = "string used by function foo1()\n";
const char * _foo2 = "string used by function foo2()\n";

A weak version definition can be introduced to identify this change.

$ cat mapfile
SUNW_1.1 {                   # Release X

SUNW_1.2 {                   # Release X+1
} SUNW_1.1;

SUNW_1.2.1 { } SUNW_1.2;     # Release X+2

$ cc -o -M mapfile -G foo.o data.o
$ pvs -dv;
        SUNW_1.2:                {SUNW_1.1};
        SUNW_1.2.1 [WEAK]:       {SUNW_1.2};

The empty version definition is signified by the weak label. These weak version definitions enable applications to verify the existence of a particular implementation detail. An application can bind to the version definition that is associated with an implementation detail that the application requires. The section Binding to a Version Definition illustrates how these definitions can be used in more detail.