15 32-Bit and 64-Bit Applications in a 64-Bit System Environment #
SUSE® Linux Enterprise Server is available for several 64-bit platforms. This does not necessarily mean that all the applications included have already been ported to 64-bit platforms. SUSE Linux Enterprise Server supports the use of 32-bit applications in a 64-bit system environment. This chapter offers a brief overview of how this support is implemented on 64-bit SUSE Linux Enterprise Server platforms.
SUSE Linux Enterprise Server for the 64-bit platforms IBM POWER, IBM IBM Z and AMD64/Intel 64 is designed so that existing 32-bit applications run in the 64-bit environment “out-of-the-box.” The corresponding 32-bit platforms are ppc for POWER, and x86 for AMD64/Intel 64. This support means that you can continue to use your preferred 32-bit applications without waiting for a corresponding 64-bit port to become available. The current POWER system runs most applications in 32-bit mode, but you can run 64-bit applications.
SUSE Linux Enterprise Server does not support compiling 32-bit applications, it only offers runtime support for 32-bit binaries.
15.1 Runtime Support #
If an application is available both for 32-bit and 64-bit environments, parallel installation of both versions is bound to lead to problems. In such cases, decide on one of the two versions and install and use this.
An exception to this rule is PAM (pluggable authentication modules). SUSE Linux Enterprise Server uses PAM in the authentication process as a layer that mediates between user and application. On a 64-bit operating system that also runs 32-bit applications it is necessary to always install both versions of a PAM module.
To be executed correctly, every application requires a range of libraries. Unfortunately, the names for the 32-bit and 64-bit versions of these libraries are identical. They must be differentiated from each other in another way.
To retain compatibility with the 32-bit version, the libraries are stored at
the same place in the system as in the 32-bit environment. The 32-bit
version of libc.so.6 is located under
/lib/libc.so.6 in both the 32-bit and 64-bit
environments.
All 64-bit libraries and object files are located in directories called
lib64. The 64-bit object files that you would normally
expect to find under /lib and
/usr/lib are now found under
/lib64 and /usr/lib64. This means
that there is space for the 32-bit libraries under /lib
and /usr/lib, so the file name for both versions can
remain unchanged.
Subdirectories of 32-bit /lib directories which contain
data content that does not depend on the word size are not moved. This
scheme conforms to LSB (Linux Standards Base) and FHS (File System Hierarchy
Standard).
15.2 Kernel Specifications #
The 64-bit kernels for AMD64/Intel 64, IBM POWER and IBM IBM Z offer both a 64-bit and a 32-bit kernel ABI (application binary interface). The latter is identical with the ABI for the corresponding 32-bit kernel. This means that the 32-bit application can communicate with the 64-bit kernel in the same way as with the 32-bit kernel.
The 32-bit emulation of system calls for a 64-bit kernel does not support
all the APIs used by system programs. This depends on the platform. For this
reason, few applications, like lspci, must be
compiled on non-POWER platforms as 64-bit programs to
function properly. On IBM IBM Z, not all ioctls are available in the
32-bit kernel ABI.
A 64-bit kernel can only load 64-bit kernel modules that have been specially compiled for this kernel. It is not possible to use 32-bit kernel modules.
Some applications require separate kernel-loadable modules. If you intend to use such a 32-bit application in a 64-bit system environment, contact the provider of this application and SUSE to make sure that the 64-bit version of the kernel-loadable module and the 32-bit compiled version of the kernel API are available for this module.