S/390 And Zseries Options - Red Hat ENTERPRISE LINUX 4 Manual

Chapter 4. GCC Command Options

4.17.5. S/390 and zSeries Options

These are the options defined for the S/390 and zSeries architecture.
-m
-mhard-float
-msoft-float
Use (do not use) the hardware floating-point instructions and registers for floating-point
operations. When
floating-point operations. When
floating-point instructions. This is the default.
-mbackchain
-mno-backchain
-mkernel-backchain
In order to provide a backchain the address of the caller's frame is stored within the callee's
stack frame. A backchain may be needed to allow debugging using tools that do not under-
stand DWARF-2 call frame information. For
all which is the default. If one of the other options is present the backchain pointer is placed
either on top of the stack frame (
Beside the different backchain location
breaking the ABI. This option is intended to be used for code which internally needs a backchain
but has to get by with a limited stack size e.g. the linux kernel. Internal unwinding code not using
DWARF-2 info has to be able to locate the return address of a function. That will be eased be the
fact that the return address of a function is placed two words below the backchain pointer.
-msmall-exec
-mno-small-exec
Generate (or do not generate) code using the
works reliably if the total executable size does not exceed 64k. The default is to use the
instruction instead, which does not have this limitation.
-m64
-m31
When is specified, generate code compliant to the GNU/Linux for S/390 ABI. When
-m31
is specified, generate code compliant to the GNU/Linux for zSeries ABI. This allows GCC
-m64
in particular to generate 64-bit instructions. For the
targets default to
s390x
-mzarch
-mesa
When
-mzarch
When is specified, generate code using the instructions available on ESA/390. Note that
-mesa
is not possible with
-mesa
ABI, the default is
the default is
-mzarch
-mmvcle
-mno-mvcle
Generate (or do not generate) code using the
is specified, use a
-mno-mvcle
is specified, functions in
-msoft-float
-mhard-float
-mkernel-backchain
.
-m64
is specified, generate code using the instructions available on z/Architecture.
. When generating code compliant to the GNU/Linux for S/390
-m64
. When generating code compliant to the GNU/Linux for zSeries ABI,
-mesa
.
loop instead. This is the default.
mvc
is specified, the compiler generates IEEE
-mno-backchain
) or on the bottom (
-mkernel-backchain
instruction to do subroutine calls. This only
bras
targets, the default is
s390
instruction to perform block moves. When
mvcle
will be used to perform
libgcc.a
no backchain is maintained at
-mbackchain
also changes stack frame layout
-m31
111
).
basr
, while the