Adding 64-bit pointer support to a 32-bit run-time library

Abstract

has extended the address space accessible to applications beyond the traditional 32-bit address space. This new address space is referred to as 64-bit virtual memory and requires a 64-bit pointer for memory access. The operating system has an additional set of new memory allocation routines that allows programs to allocate and release 64-bit memory. In OpenVMS Alpha version 7.0, this set of routines is the only mechanism available to acquire 64-bit memory. For application programs to take advantage of these new OpenVMS programming interfaces, high-level programming languages such as C had to support 64-bit pointers. Both the C compiler and the C runtime library required changes to provide this support. The compiler needed to understand both 32-bit and 64-bit pointers, and the run-time library needed to accept and return such pointers. The compiler has a new qualifier called /pointer_size, which sets the default pointer size for the compilation to either 32 bits or 64 bits. Also added to the compiler are pragmas (directives) that can be used within the source code to change the active pointer size. An application program is not required to compile each module using the same /pointer_size qualifier; some modules may use 32-bit pointers while others use 64-bit pointers. Benson, Noel, and Peterson describe these compiler enhancements. The DEC C User’s Guide for OpenVMS Systems documents the qualifier and the pragmas. The C run-time library added 64-bit pointer support either by modifying the existing interface to a function or by adding a second interface to the same function. Public header files define the C run-time library interfaces. These header files contain the publicly accessible function prototypes and structure definitions. The library documentation and header files are shipped with the C compiler; the C run-time library ships with the operating system. This paper discusses all phases of the enhancements to the C run-time library, from project concepts through the analysis, the design, and finally the implementation. The DEC C Runtime Library Reference Manual for OpenVMS Systems contains user documentation regarding the changes.