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Run-Time Library Reference Manual for OpenVMS Systems

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1.10.2 Obtaining 64-Bit Pointers to Memory

The HP C RTL has many functions that return pointers to newly allocated memory. In each of these functions, the application owns the memory pointed to and is responsible for freeing that memory.

Functions that allocate memory are:


Each of these functions have a 32-bit and a 64-bit implementation. When the /POINTER_SIZE qualifier is used, the following functions can also be called:

_malloc32 , _malloc64
_calloc32 , _calloc64
_realloc32 , _realloc64
_strdup32 , _strdup64

When /POINTER_SIZE=32 is specified, all malloc calls default to _malloc32 .

When /POINTER_SIZE=64 is specified, all malloc calls default to _malloc64 .

Regardless of whether the application calls a 32-bit or 64-bit memory allocation routine, there is still a single free function. This function accepts either pointer size.

Be aware that the memory allocation functions are the only ones that return pointers to 64-bit memory. All HP C RTL structure pointers returned to the calling application (such as a FILE, WINDOW, or DIR) are always 32-bit pointers. This allows both 32-bit and 64-bit callers to pass these structure pointers within the application.

1.10.3 HP C Header Files

The header files distributed with OpenVMS support 64-bit pointers. Each function prototype whose signature contains a pointer is constructed to indicate the size of the pointer accepted.

A 32-bit pointer can be passed as an argument to functions that accept either a 32-bit or 64-bit pointer for that argument.

A 64-bit pointer, however, cannot be passed as an argument to a function that accepts a 32-bit pointer. Attempts to do this are diagnosed by the compiler with a MAYLOSEDATA message. The diagnostic message IMPLICITFUNC means the compiler can do no additional pointer-size validation for calls to that function. If this function is an HP C RTL function, refer to the reference section of this manual for the name of the header file that defines that function.

You might find the following pointer-size compiler diagnostics useful:

    A function prototype was not found before using the specified function. The compiler and run-time system rely on prototype definitions to detect incorrect pointer-size usage. Failure to include the proper header files can lead to incorrect results and/or pointer truncation.
    A truncation is necessary to do this operation. The operation could be passing a 64-bit pointer to a function that does not support a 64-bit pointer in the given context. It could also be a function returning a 64-bit pointer to a calling application that is trying to store that return value in a 32-bit pointer.
    This message (when enabled) helps expose real MAYLOSEDATA messages that are being suppressed because of a cast operation. To enable this warning, compile with the qualifier /WARNINGS=ENABLE=MAYHIDELOSS.

1.10.4 Functions Affected

The HP C RTL accommodates applications that use only 32-bit pointers, only 64-bit pointers, or combinations of both. To use 64-bit memory, you must, at a minimum, recompile and relink an application. The amount of source code change required depends on the application itself, calls to other run-time libraries, and the combinations of pointer sizes used.

With respect to 64-bit pointer support, the functions in the HP C RTL fall into four categories:

  • Functions not impacted by choice of pointer size
  • Functions enhanced to accept either pointer size
  • Functions having a 32-bit and 64-bit implementation
  • Functions that accept only 32-bit pointers

From an application developer's perspective, the first two types of functions are the easiest to use in either a single- or mixed-pointer mode.

The third type requires no modifications when used in a single-pointer compilation, but might require source code changes when used in a mixed-pointer mode.

The fourth type requires careful attention whenever 64-bit pointers are used. No Pointer-Size Impact

The choice of pointer size has no impact on a function if its prototype contains no pointer-related parameters or return values. The mathematical functions are good examples of this.

Even some functions in this category that do have pointers in their prototype are not impacted by pointer size. For example, strerror has the prototype:

char * strerror (int error_number);

This function returns a pointer to a character string, but this string is allocated by the HP C RTL. As a result, to support both 32-bit and 64-bit applications, these types of pointers are guaranteed to fit in a 32-bit pointer. Functions Accepting Both Pointer Sizes

The Alpha architecture supports 64-bit pointers. The OpenVMS Alpha calling standard specifies that all arguments are actually passed as 64-bit values. Before OpenVMS Alpha Version 7.0, all 32-bit addresses passed to procedures were sign-extended into this 64-bit parameter. The called function declared the parameters as 32-bit addresses, which caused the compiler to generate 32-bit instructions (such as LDL) to manipulate these parameters.

Many functions in the HP C RTL are enhanced to receive the full 64-bit address. For example, consider strlen :

size_t strlen (const char *string);

The only pointer in this function is the character-string pointer. If the caller passes a 32-bit pointer, the function works with the sign-extended 64-bit address. If the caller passes a 64-bit address, the function works directly with that address.

The HP C RTL continues to have only a single entry point for functions in this category. There are no source-code changes required to add any of the four pointer-size options for functions of this type. The OpenVMS documentation refers to these functions as 64-bit friendly. Functions with Two Implementations

There are many reasons why a function might need one implementation for 32-bit pointers and another for 64-bit pointers. Some of these reasons include:

  • The pointer size of the return value is the same size as the pointer size of one of the arguments. If the argument is 32 bits, the return value is 32 bits. If the argument is 64 bits, the return value is 64 bits.
  • One of the arguments is a pointer to an object whose size is pointer-size sensitive. To know how many bytes are being pointed to, the function must know if the code was compiled in 32-bit or 64-bit pointer-size mode.
  • The function returns the address of dynamically allocated memory. The memory is allocated in 32-bit space when compiled for 32-bit pointers, and is allocated in 64-bit space when compiled for 64-bit pointers.

From the application developer's point of view, there are three function prototypes for each of these functions. The <string.h> header file contains many functions whose return value is dependent upon the pointer size used as the first argument to the function call. For example, consider the memset function. The header file defines three entry points for this function:

void * memset   (void *memory_pointer, int character, size_t size);
void *_memset32 (void *memory_pointer, int character, size_t size);
void *_memset64 (void *memory_pointer, int character, size_t size);

The first prototype is the function that your application would currently call if using this function. The compiler changes a call to memset into a call to either _memset32 when compiled with /POINTER_SIZE=32, or _memset64 when compiled with /POINTER_SIZE=64.

You can override this default behavior by directly calling either the 32-bit or the 64-bit form of the function. This accommodates applications using mixed-pointer sizes, regardless of the default pointer size specified with the /POINTER_SIZE qualifier.

If the application is compiled without specifying the /POINTER_SIZE qualifier, neither the 32-bit specific nor the 64-bit specific function prototypes are defined. In this case, the compiler automatically calls the 32-bit interface for all interfaces having dual implementations.

Table 1-6 shows the HP C RTL functions that have dual implementations to support 64-bit pointer size. When compiling with the /POINTER_SIZE qualifier, calls to the unmodified function names are changed to calls to the function interface that matches the pointer size specified on the qualifier.

Table 1-6 Functions with Dual Implementations
basename bsearch calloc catgets
ctermid cuserid dirname fgetname
fgets fgetws gcvt getcwd
getname getpwent getpwnam getpwnam_r
getpwuid getpwuid_r gets index
longname malloc mbsrtowcs memccpy
memchr memcpy memmove memset
mktemp mmap qsort readv
realloc rindex strcat strchr
strcpy strdup strncat strncpy
strpbrk strptime strrchr strsep
strstr strtod strtok strtok_r
strtol strtoll strtoq strtoul
strtoull strtouq tmpnam wcscat
wcschr wcscpy wcsncat wcsncpy
wcspbrk wcsrchr wcsrtombs wcsstr
wcstok wcstol wcstoul wcswcs
wmemchr wmemcpy wmemmove wmemset
writev glob globfree  

Table 1-7 shows the TCP/IP socket routines that have dual implementations to support 64-bit pointer size.

Table 1-7 Socket Routines with Dual Implementations
freeaddrinfo getaddrinfo
recvmsg sendmsg Functions Requiring Explicit use of 64-Bit Structures

Some functions require explicit use of 64-bit structures when compiling /POINTER_SIZE=LONG. This is necessary for functions that have recently had 64-bit support added to avoid unexpected runtime errors by inadvertently mixing 32-bit and 64-bit versions of structures.

Consider the following functions:

getaddrinfo        getpwnam
freeaddrinfo       getpwnam_r
getpwuid           getpwent
sendmsg            getpwent_r

These functions previously offered 32-bit support only, even when compiled with /POINTER_SIZE=LONG. In order to preserve the previous behavior of 32-bit pointer support in those functions even when compiled with /POINTER_SIZE=LONG, these seven functions do not follow the normal convention for 32-bit and 64-bit support as documented in the previous section.

The following variants of these functions, and the corresponding structures they use, have been added to the C RTL to provide 64-bit support:

Function                        Structure
--------                        ---------
__getaddrinfo32                 __addrinfo32
__getaddrinfo64                 __addrinfo64
__freeaddrinfo32                __addrinfo32
__freeaddrinfo64                __addrinfo64
__recvmsg32                     __msghdr32
__recvmsg64                     __msghdr64
__sendmsg32                     __msghdr32
__sendmsg64                     __msghdr64
__32_getpwnam                   __passwd32
__64_getpwnam                   __passwd64

_getpwnam_r32 __passwd32
_getpwnam_r64 __passwd64

__32_getpwuid                   __passwd32
__64_getpwuid                   __passwd64

_getpwuid_r32  __passwd32
_getpwuid_r64  __passwd64

__32_getpwent                   __passwd32
__64_getpwent                   __passwd64

When compiling the standard versions of these functions, the following behavior occurs:

  • With /POINTER_SIZE=32 specified, the compiler converts the call to the 32-bit version of the function. For example, getaddrinfo is converted to __getaddrinfo32 .
  • With /POINTER_SIZE=64 specified, the compiler converts the call to the 64-bit version of the function. For example, getaddrinfo is converted to __getaddrinfo64 .
  • When the /POINTER_SIZE qualifier is not specified, neither the 32-bit-specific nor the 64-bit-specific function prototypes are defined.

However, a similar conversion of the corresponding structures does not occur for these functions. This behavior is necessary because these structures existed before OpenVMS Version 7.3-2 as 32-bit versions only, even when compiled with /POINTER_SIZE=LONG. Implicitly changing the size of the structure could result in unexpected run-time errors.

When compiling programs that use the standard version of these functions for 64-bit support, you must use the 64-bit-specific definition of the related structure. With /POINTER_SIZE=64 specified, compiling a program with the standard function name and standard structure definition will result in compiler PTRMISMATCH warning messages.

For example, the following program uses the getaddrinfo and freeaddrinfo routines, along with the standard definition of the addrinfo structure. Compiling this program results in the warning messages shown:

$ type test.c
#include <netdb.h>

int main ()
    struct addrinfo *ai;

    getaddrinfo ("althea", 0, 0, &ai);
    freeaddrinfo (ai);
    return 0;

$ cc /pointer_size=64 TEST.C

    getaddrinfo ("althea", 0, 0, &ai);
%CC-W-PTRMISMATCH, In this statement, the referenced type of the pointer value
"&ai" is "long pointer to struct addrinfo", which is not compatible with "long
pointer to struct __addrinfo64".
at line number 7 in file TEST.C;1

    freeaddrinfo (ai);
%CC-W-PTRMISMATCH, In this statement, the referenced type of the pointer value
"ai" is "struct addrinfo", which is not compatible with "struct __addrinfo64".
at line number 8 in file TEST.C;1

When compiling for 64 bits, you need to use the 64-bit-specific version of the related structure. In the previous example, the declaration of the ai structure could be changed to the following:

struct __addrinfo64 *ai;

Or, to provide flexibility between 32-bit and 64-bit compilations, the ai structure could be declared as follows:

    struct __addrinfo64 *ai;
    struct __addrinfo32 *ai;
#endif Functions Restricted to 32-Bit Pointers

A few functions in the HP C RTL do not support 64-bit pointers. If you try to pass a 64-bit pointer to one of these functions, the compiler generates a %CC-W-MAYLOSEDATA warning. Applications compiled with /POINTER_SIZE=64 might need to be modified to avoid passing 64-bit pointers to these functions.

Table 1-8 shows the functions restricted to using 32-bit pointers. The HP C RTL offers no 64-bit support for these functions. You must ensure that only 32-bit pointers are used with these functions.

Table 1-8 Functions Restricted to 32-Bit Pointers
atexit frexp ioctl setbuf
execv getopt modf setstate
execve iconv putenv setvbuf
execvp initstate    

Table 1-9 shows functions that make callbacks to user-supplied functions as part of processing that function call. The callback procedures are not passed 64-bit pointers.

Table 1-9 Callbacks that Pass Only 32-Bit Pointers
decc$from_vms decc$to_vms
ftw tputs

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