Identifying a Platform Capability

A platform capability of an object identifies the platform name of the systems that the object, or specific symbols within the object, can execute upon. Multiple platform capabilities can be defined. This identification is very specific, and takes precedence over any other capability types.

The platform name of a system can be displayed by the utility uname(1) with the -i option.

A platform capability requirement can be defined using the following mapfile syntax.

        $mapfile_version 2
        CAPABILITY {
                PLATFORM  = platform_name...;
                PLATFORM += platform_name...;
                PLATFORM -= platform_name...;
        };

The PLATFORM attribute is qualified with one or more platform names. The “+=” form of assignment augments the platform capabilities specified by the input objects, while the “=” form overrides them. The “-=" form of assignment is used to exclude platform capabilities from the output object. The following SPARC example identifies the object foo.so.1 as being specific to the SUNW,SPARC-Enterprise platform.

$ cat mapfile
$mapfile_version 2
CAPABILITY {
        PLATFORM = 'SUNW,SPARC-Enterprise';
};
$ cc -o foo.so.1 -G -K pic -Mmapfile foo.c -lc
$ elfdump -H foo.so.1

Capabilities Section:  .SUNW_cap

 Object Capabilities:
     index  tag               value
       [0]  CA_SUNW_PLAT     SUNW,SPARC-Enterprise

Relocatable objects can define platform capabilities. These capabilities are gathered together to define the final capability requirements of the object being built.

The platform capability of an object can be controlled explicitly from a mapfile by using the “=” form of assignment to override any platform capabilities that might be provided from any input relocatable objects. An empty PLATFORM attribute used with the “=” form of assignment effectively removes any platform capabilities requirement from the object being built.

A platform capability requirement defined in a dynamic object is validated by the runtime linker against the platform name of the system. The object is only used if one of the platform names recorded in the object match the platform name of the system.

Targeting code to a specific platform can be useful in some instances, however the development of a hardware capabilities family can provide greater flexibility, and is recommended. Hardware capabilities families can provide for optimized code to be exercised on a broader range of systems.