Full Generic System V ABI

_nameThis gives a system service name that follows the ANSI C conventionof reserving symbols beginning with an underscore, such as _ r e a d.Although many system services have two names, two exceptions exist to thissynonym convention. System V defines both e x i t and _ e x i t as different facilities.Consequently, the symbols e x i t and _ e x i t have no synonyms and refer todifferent services.Implementation of libsys RoutinesAll ABI-conforming systems must provide a l i b s y s entry point for all routineslisted as belonging to this library. However, only the routines necessary to providethe source-level programming interfaces required to be defined in the X/OpenCAE Specification, Issue 4.2 and defined in the System V Interface Definition, ThirdEdition sections BA_OS, BA_LIB, and KE_OS, as described in the introduction tothe System V ABI, must be implemented on a conforming system (see the ConformanceRule in chapter 1). For example, this means that the routinem e m c n t l(RT_OS) need not be fully implemented on an ABI-conforming system,though the entry point for this function must be present in the library.Routines not required for the System V Interface Definition, Third Edition sectionslisted above or X/Open CAE Specification, Issue 4.2 may or may not be implemented,at the discretion of the system implementor. Unimplemented routinesmust be represented in the library by a stub that when called causes failure andsets the global variable e r r n o to the value E N O S Y S.XXEEVendor ExtensionsBesides the services listed above, libsys may contain other symbols. An ABIconformingsystem vendor may add a symbol to the system library to providevendor-specific services. The ABI does not define these services, and programsusing these services are not ABI-conforming. Nonetheless, the ABI defines arecommended extension mechanism, providing a way to avoid conflict among theservices from multiple vendors.A symbol of the form _ $ v e n d o r .company provides an operating system entry forthe vendor named company. The system library does not have unadorned alternativesfor these names. Conventionally, a vendor uses the single name to providemultiple services, letting the first argument to _ $ v e n d o r .company select amongthe alternatives. As an example, the ‘‘XYZ Computer Company’’ might add_ $ v e n d o r . x y z to the system library.ESystem Library 6-9