Applies to openSUSE Leap 15

8 32-Bit and 64-Bit Applications in a 64-Bit System Environment

openSUSE® Leap is available for 64-bit platforms. This does not necessarily mean that all the applications included have already been ported to 64-bit platforms. openSUSE Leap 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 openSUSE Leap platforms. It explains how 32-bit applications are executed and how 32-bit applications should be compiled to enable them to run both in 32-bit and 64-bit system environments. Additionally, find information about the kernel API and an explanation of how 32-bit applications can run under a 64-bit kernel.

openSUSE Leap for the 64-bit platforms amd64 and Intel 64 is designed so that existing 32-bit applications run in the 64-bit environment out-of-the-box. 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.

8.1 Runtime Support

Important
Important: Conflicts Between Application Versions

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). openSUSE Leap 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).

8.2 Software Development

All 64-bit architectures support the development of 64-bit objects. The level of support for 32-bit compiling depends on the architecture. These are the various implementation options for the toolchain from GCC (GNU Compiler Collection) and binutils, which include the assembler as and the linker ld:

Both 32-bit and 64-bit objects can be generated with a biarch development toolchain. A biarch development toolchain allows generation of 32-bit and 64-bit objects. The compilation of 64-bit objects is the default on almost all platforms. 32-bit objects can be generated if special flags are used. This special flag is -m32 for GCC. The flags for the binutils are architecture-dependent, but GCC transfers the correct flags to linkers and assemblers. A biarch development toolchain currently exists for amd64 (supports development for x86 and amd64 instructions), for IBM Z and for POWER. 32-bit objects are normally created on the POWER platform. The -m64 flag must be used to generate 64-bit objects.

All header files must be written in an architecture-independent form. The installed 32-bit and 64-bit libraries must have an API (application programming interface) that matches the installed header files. The normal openSUSE Leap environment is designed according to this principle. In the case of manually updated libraries, resolve these issues yourself.

8.3 Software Compilation on Biarch Platforms

To develop binaries for the other architecture on a biarch architecture, the respective libraries for the second architecture must additionally be installed. These packages are called rpmname-32bit. You also need the respective headers and libraries from the rpmname-devel packages and the development libraries for the second architecture from rpmname-devel-32bit.

For example, to compile a program that uses libaio on a system with a 32-bit second architecture (AMD64/Intel 64), you need the following RPMs:

libaio-32bit

32-bit runtime package

libaio-devel-32bit

Headers and libraries for 32-bit development

libaio

64-bit runtime package

libaio-devel

64-bit development headers and libraries

Most open source programs use an autoconf-based program configuration. To use autoconf for configuring a program for the second architecture, overwrite the normal compiler and linker settings of autoconf by running the configure script with additional environment variables.

The following example refers to an AMD64/Intel 64 system with x86 as the second architecture.

  1. Use the 32-bit compiler:

    CC="gcc -m32"
  2. Instruct the linker to process 32-bit objects (always use gcc as the linker front-end):

    LD="gcc -m32"
  3. Set the assembler to generate 32-bit objects:

    AS="gcc -c -m32"
  4. Specify linker flags, such as the location of 32-bit libraries, for example:

    LDFLAGS="-L/usr/lib"
  5. Specify the location for the 32-bit object code libraries:

    --libdir=/usr/lib
  6. Specify the location for the 32-bit X libraries:

    --x-libraries=/usr/lib

Not all of these variables are needed for every program. Adapt them to the respective program.

An example configure call to compile a native 32-bit application on AMD64/Intel 64 could appear as follows:

CC="gcc -m32"
LDFLAGS="-L/usr/lib;"
./configure --prefix=/usr --libdir=/usr/lib --x-libraries=/usr/lib
make
make install

8.4 Kernel Specifications

The 64-bit kernels for AMD64/Intel 64 offer both a 64-bit and a 32-bit kernel ABI (application binary interface). The latter is identical to 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.

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.

Tip
Tip: Kernel-loadable 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.

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