Red Hat ENTERPRISE LINUX 4 Manual

Also see for ENTERPRISE LINUX 4 - DEVELOPER TOOLS GUIDE: Installation guide Installation guide Tuning guide Installation guide Manual

Contents

Chapter 4. GCC Command Options 93In addition, each of these target machine types can have its own special options, starting with -m,to choose among various hardware models or configurations--for example, 68010 vs 68020, float-ing coprocessor or none. A single installed version of the compiler can compile for any model orconfiguration, according to the options specified.Some configurations of the compiler also support additional special options, usually for compatibilitywith other compilers on the same platform.These options are defined by the macro TARGET_SWITCHES in the machine description. The defaultfor the options is also defined by that macro, which enables you to change the defaults.4.17.1. IBM RS/6000 and PowerPC OptionsThese -m options are defined for the IBM RS/6000 and PowerPC:-mpower-mno-power-mpower2-mno-power2-mpowerpc-mno-powerpc-mpowerpc-gpopt-mno-powerpc-gpopt-mpowerpc-gfxopt-mno-powerpc-gfxopt-mpowerpc64-mno-powerpc64GCC supports two related instruction set architectures for the RS/6000 and PowerPC. ThePOWER instruction set are those instructions supported by the rios chip set used in the originalRS/6000 systems and the PowerPC instruction set is the architecture of the Motorola MPC5xx,MPC6xx, MPC8xx microprocessors, and the IBM 4xx microprocessors.Neither architecture is a subset of the other. However there is a large common subset of in-structions supported by both. An MQ register is included in processors supporting the POWERarchitecture.You use these options to specify which instructions are available on the processor you areusing. The default value of these options is determined when configuring GCC. Specifyingthe -mcpu=cpu_type overrides the specification of these options. We recommend you use the-mcpu=cpu_type option rather than the options listed above.The -mpower option allows GCC to generate instructions that are found only in the POWERarchitecture and to use the MQ register. Specifying -mpower2 implies -power and also allowsGCC to generate instructions that are present in the POWER2 architecture but not the originalPOWER architecture.The -mpowerpc option allows GCC to generate instructions that are found only in the 32-bit sub-set of the PowerPC architecture. Specifying -mpowerpc-gpopt implies -mpowerpc and alsoallows GCC to use the optional PowerPC architecture instructions in the General Purpose group,including floating-point square root. Specifying -mpowerpc-gfxopt implies -mpowerpc andalso allows GCC to use the optional PowerPC architecture instructions in the Graphics group,including floating-point select.The -mpowerpc64 option allows GCC to generate the additional 64-bit instructions that arefound in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities.GCC defaults to -mno-powerpc64.If you specify both -mno-power and -mno-powerpc, GCC will use only the instructions inthe common subset of both architectures plus some special AIX common-mode calls, and will