S/390 and zSeries Options

These are the -m options defined for the S/390 and zSeries architecture.

-mhard-float

-msoft-float

Use (do not use) the hardware floating-point instructions and registers for floating-point operations. When -msoft-float is specified, functions in libgcc.a will be used to perform floating-point operations. When -mhard-float is specified, the compiler generates IEEE floating-point instructions. This is the default.

-mbackchain

-mno-backchain

Generate (or do not generate) code which maintains an explicit backchain within the stack frame that points to the caller's frame. This is currently needed to allow debugging. The default is to generate the backchain.

-msmall-exec

-mno-small-exec

Generate (or do not generate) code using the bras instruction to do subroutine calls. This only works reliably if the total executable size does not exceed 64k. The default is to use the basr instruction instead, which does not have this limitation.

-m64

-m31

When -m31 is specified, generate code compliant to the Linux for S/390 ABI. When -m64 is specified, generate code compliant to the Linux for zSeries ABI. This allows GCC in particular to generate 64-bit instructions. For the s390 targets, the default is -m31, while the s390x targets default to -m64.

-mzarch

-mesa

When -mzarch is specified, generate code using the instructions available on z/Architecture. When -mesa is specified, generate code using the instructions available on ESA/390. Note that -mesa is not possible with -m64. For the s390 targets, the default is -mesa, while the s390x targets default to -mzarch.

-mmvcle

-mno-mvcle

Generate (or do not generate) code using the mvcle instruction to perform block moves. When -mno-mvcle is specified, use a mvc loop instead. This is the default.

-mdebug

-mno-debug

Print (or do not print) additional debug information when compiling. The default is to not print debug information.

-march=arch

Generate code that will run on arch, which is the name of system representing a certain processor type. Possible values for cpu-type are g5, g6 and z900.

-mcpu=arch

Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of available instructions. The list of arch values is the same as for -march.