Redefining an Interface

One scenario is the consumption of an ISV specific interface into a public standard interface.

From the previous libfoo.so.1 example, assume that in Release X+2, the version definition SUNW_1.1 is subdivided into two standard releases, STAND_A and STAND_B. To preserve compatibility, the SUNW_1.1 version definition must be maintained. In this example, this version definition is expressed as inheriting the two standard definitions.

$ pvs -dsv libfoo.so.1
        libfoo.so.1:
                _end;
                _GLOBAL_OFFSET_TABLE_;
                _DYNAMIC;
                _edata;
                _PROCEDURE_LINKAGE_TABLE_;
                _etext;
        SUNW_1.1:           {STAND_A, STAND_B}:
                SUNW_1.1;
        SUNW_1.2:           {SUNW_1.1}:
                bar;
        STAND_A:
                foo1;
                STAND_A;
        STAND_B:
                foo2;
                STAND_B;

If the only requirement of application prog is the interface symbol foo1, the application will have a single dependency on the version definition STAND_A. This precludes running prog on a system where libfoo.so.1 is less than Release X+2. The version definition STAND_A did not exist in previous releases, even though the interface foo1 did.

The application prog can be built to align its requirement with previous releases by creating a dependency on SUNW_1.1.

$ cat mapfile
$mapfile_version 2
DEPEND_VERSIONS libfoo.so {
        ALLOW = SUNW_1.1;
        REQURE = SUNW_1.1;
};
$ cat prog
extern void foo1();

main()
{
        foo1();
}
$ cc -M mapfile -o prog prog.c -L. -R. -lfoo
$ pvs -r prog
        libfoo.so.1 (SUNW_1.1);

This explicit dependency is sufficient to encapsulate the true dependency requirements. This dependency satisfies compatibility with older releases.