RX Options#
These command-line options are defined for RX targets:
- -m64bit-doubles, -m32bit-doubles#
Make the
double
data type be 64 bits (-m64bit-doubles
) or 32 bits (-m32bit-doubles
) in size. The default is-m32bit-doubles
.Note
RX floating-point hardware only works on 32-bit values, which is why the default is
-m32bit-doubles
.
- -fpu, -nofpu#
Enables (
-fpu
) or disables (-nofpu
) the use of RX floating-point hardware. The default is enabled for the RX600 series and disabled for the RX200 series.Floating-point instructions are only generated for 32-bit floating-point values, however, so the FPU hardware is not used for doubles if the
-m64bit-doubles
option is used.Note
If the
-fpu
option is enabled then-funsafe-math-optimizations
is also enabled automatically. This is because the RX FPU instructions are themselves unsafe.
- -mcpu=name#
Selects the type of RX CPU to be targeted. Currently three types are supported, the generic
RX600
andRX200
series hardware and the specificRX610
CPU. The default isRX600
.The only difference between
RX600
andRX610
is that theRX610
does not support theMVTIPL
instruction.The
RX200
series does not have a hardware floating-point unit and so-nofpu
is enabled by default when this type is selected.
- -mbig-endian-data, -mlittle-endian-data#
Store data (but not code) in the big-endian format. The default is
-mlittle-endian-data
, i.e. to store data in the little-endian format.
- -msmall-data-limit=N#
Specifies the maximum size in bytes of global and static variables which can be placed into the small data area. Using the small data area can lead to smaller and faster code, but the size of area is limited and it is up to the programmer to ensure that the area does not overflow. Also when the small data area is used one of the RX’s registers (usually
r13
) is reserved for use pointing to this area, so it is no longer available for use by the compiler. This could result in slower and/or larger code if variables are pushed onto the stack instead of being held in this register.Note
Common variables (variables that have not been initialized) and constants are not placed into the small data area as they are assigned to other sections in the output executable.
The default value is zero, which disables this feature. Note, this feature is not enabled by default with higher optimization levels (
-O2
etc) because of the potentially detrimental effects of reserving a register. It is up to the programmer to experiment and discover whether this feature is of benefit to their program. See the description of the-mpid
option for a description of how the actual register to hold the small data area pointer is chosen.
- -msim, -mno-sim#
Use the simulator runtime. The default is to use the libgloss board-specific runtime.
- -mas100-syntax, -mno-as100-syntax#
When generating assembler output use a syntax that is compatible with Renesas’s AS100 assembler. This syntax can also be handled by the GAS assembler, but it has some restrictions so it is not generated by default.
- -mmax-constant-size=N#
Specifies the maximum size, in bytes, of a constant that can be used as an operand in a RX instruction. Although the RX instruction set does allow constants of up to 4 bytes in length to be used in instructions, a longer value equates to a longer instruction. Thus in some circumstances it can be beneficial to restrict the size of constants that are used in instructions. Constants that are too big are instead placed into a constant pool and referenced via register indirection.
The value
N
can be between 0 and 4. A value of 0 (the default) or 4 means that constants of any size are allowed.
- -mrelax#
Enable linker relaxation. Linker relaxation is a process whereby the linker attempts to reduce the size of a program by finding shorter versions of various instructions. Disabled by default.
- -mint-register=N#
Specify the number of registers to reserve for fast interrupt handler functions. The value
N
can be between 0 and 4. A value of 1 means that registerr13
is reserved for the exclusive use of fast interrupt handlers. A value of 2 reservesr13
andr12
. A value of 3 reservesr13
,r12
andr11
, and a value of 4 reservesr13
throughr10
. A value of 0, the default, does not reserve any registers.
- -msave-acc-in-interrupts#
Specifies that interrupt handler functions should preserve the accumulator register. This is only necessary if normal code might use the accumulator register, for example because it performs 64-bit multiplications. The default is to ignore the accumulator as this makes the interrupt handlers faster.
- -mpid, -mno-pid#
Enables the generation of position independent data. When enabled any access to constant data is done via an offset from a base address held in a register. This allows the location of constant data to be determined at run time without requiring the executable to be relocated, which is a benefit to embedded applications with tight memory constraints. Data that can be modified is not affected by this option.
Note, using this feature reserves a register, usually
r13
, for the constant data base address. This can result in slower and/or larger code, especially in complicated functions.The actual register chosen to hold the constant data base address depends upon whether the
-msmall-data-limit
and/or the-mint-register
command-line options are enabled. Starting with registerr13
and proceeding downwards, registers are allocated first to satisfy the requirements of-mint-register
, then-mpid
and finally-msmall-data-limit
. Thus it is possible for the small data area register to ber8
if both-mint-register=4
and-mpid
are specified on the command line.By default this feature is not enabled. The default can be restored via the
-mno-pid
command-line option.
- -mno-warn-multiple-fast-interrupts, -mwarn-multiple-fast-interrupts#
Prevents GCC from issuing a warning message if it finds more than one fast interrupt handler when it is compiling a file. The default is to issue a warning for each extra fast interrupt handler found, as the RX only supports one such interrupt.
- -mallow-string-insns, -mno-allow-string-insns#
Enables or disables the use of the string manipulation instructions
SMOVF
,SCMPU
,SMOVB
,SMOVU
,SUNTIL
SWHILE
and also theRMPA
instruction. These instructions may prefetch data, which is not safe to do if accessing an I/O register. (See section 12.2.7 of the RX62N Group User’s Manual for more information).The default is to allow these instructions, but it is not possible for GCC to reliably detect all circumstances where a string instruction might be used to access an I/O register, so their use cannot be disabled automatically. Instead it is reliant upon the programmer to use the
-mno-allow-string-insns
option if their program accesses I/O space.When the instructions are enabled GCC defines the C preprocessor symbol
__RX_ALLOW_STRING_INSNS__
, otherwise it defines the symbol__RX_DISALLOW_STRING_INSNS__
.
- -mjsr, -mno-jsr#
Use only (or not only)
JSR
instructions to access functions. This option can be used when code size exceeds the range ofBSR
instructions. Note that-mno-jsr
does not mean to not useJSR
but instead means that any type of branch may be used.
Note
The generic GCC command-line option -ffixed-reg
has special significance to the RX port when used with the
interrupt
function attribute. This attribute indicates a
function intended to process fast interrupts. GCC ensures
that it only uses the registers r10
, r11
, r12
and/or r13
and only provided that the normal use of the
corresponding registers have been restricted via the
-ffixed-reg
or -mint-register
command-line
options.