AIX Version 4.3 Differences Guide

and an execution environment. The 64-bit XCOFF magic number implies a 64-bit
PowerPC processor and 64-bit execution mode on that processor.
The magic number keeps the linkage editor from binding 64-bit programs with
32-bit programs and keeps the loader from trying to execute 64-bit programs on
32-bit hardware.
The magic number is defined in the header file /usr/include/filehdr.h and has the
name U803XTOCMAGIC with the value 0757.
3.2.4 Device Drivers
AIX 4.3 supports 64-bit applications on 64-bit PowerPC hosts in addition to
maintaining support for 32-bit applications on all other supported hosts. Thus, on
64-bit hosts, both 32-bit and 64-bit applications can run simultaneously. To
minimize the impact of adding 64-bit support, the kernel continues to run in 32-bit
mode but provides interfaces to 64-bit applications by remapping the 64-bit
application space address into a 32-bit address for the kernel. Thus, the following
is true for device drivers in general and I/O drivers specifically:
• 32-bit versions of device drivers will operate correctly without change on AIX
Version 4.3 in support of 32-bit applications.
• 64-bit applications require modification of only the entry points (such as
ioctl()s) for proper operation.
The 4/8/8 model requires two primary changes for an I/O device driver:
• Providing ioctl support for 64-bit applications.
• Ensuring that structures describing fixed sized entities are size-invariant
between both 32-bit and 64-bit applications.
3.2.4.1 Changes to ioctl()
The third argument of an ioctl call is referred to as the arg parameter. For some
ioctls, the arg parameter can be a pointer. For AIX 4.3, the kernel guarantees that
the arg parameter received by a device driver is always a 32-bit value. For 64-bit
applications, the kernel will remap the address to a 32-bit address. Often, the arg
parameter is a pointer to a data structure that may contain additional pointers.
The kernel has no knowledge of this and, as a result, it is the device driver's
responsibility to interpret these correctly. Device drivers that support 64-bit
embedded pointers need to notify the kernel of this by setting the DEV_64BIT
define for the d_opts flag passed to the devswadd() call from the config entry
point of the device driver. For example a 64-bit-enabled SMP driver would use the
following code segment:
devsw_struct.d_opts = DEV_MPSAFE | DEV_64BIT;
devswadd(devno,&devsw_struct);
For device drivers that do not set the DEV_64BIT flag, all ioctls from 64-bit
applications will fail with an errno of EINVAL.
Since data structures with embedded pointers cannot remain size-invariant
between 32-bit and 64-bit applications, a 64-bit-enabled device driver will need to
maintain an internal-use-only 64-bit equivalent (recall the device driver will be
compiled for 32-bit mode) of all such structures that can be passed as arg
parameters. This can be accomplished by cloning the structure definition and
replacing all pointers with type ptr64 (defined in types.h as unsigned long long).
64-Bit Enablement 49