AIX Version 4.3 Differences Guide

3.2.4.2 Parameter Passing Examples
For example, assume a device driver’s shipped header file has struct A, and a
device driver supports an ioctl call whose arg parameter is the address of struct
A:
struct A {
int aaa;
char *bbb;
char c;
int *ddd;
}
For a 32-bit application using struct A as the arg parameter of an ioctl, the device
driver can recast the arg parameter as struct A. However, if the device driver
determines the caller is a 64-bit application (through a call to the IS64U kernel
macro), then the device driver will have to recast struct A to a new struct A64
defined as:
struct A64 {
int aaa;
ptr64 bbb;
char c;
ptr64 ddd;
}
The code segment of the device driver for this ioctl is similar to this:
.
.
.
if (IS64U) {
/* The caller is a 64-bit application */
x = (struct A64 *) arg;
.
.
.
} else {
/* The caller is a 32-bit application */
x = (struct A *) arg;
.
.
.
}
The following naming conventions are used to create the device driver’s 64-bit
equivalent structure:
• The 64-bit equivalent structure used by the device driver is included in the
same shipped header file.
• It has a comment indicating that this is used for device drivers only and not
applications.
• The name of the 64-bit equivalent structure is that of the original structure but
with a 64 appended (for example, for sc_iocmd, it will be sc_iocmd64).
For the device driver to manipulate the 64-bit addresses, new 64-bit kernel
services are provided. These kernel services support 32-bit unremapped
addresses as well as 32-bit remapped addresses and 64-bit addresses. Thus all
50 AIX Version 4.3 Differences Guide