3.17.10 MIPS Options

-EB

Generate big-endian code.

-EL

Generate little-endian code. This is the default for mips*el-*-* configurations.

-march=arch

Generate code that will run on arch, which can be the name of a generic MIPS ISA, or the name of a particular processor. The ISA names are: mips1, mips2, mips3, mips4, mips32, mips32r2, and mips64. The processor names are: 4kc, 4kp, 5kc, 20kc, m4k, r2000, r3000, r3900, r4000, r4400, r4600, r4650, r6000, r8000, rm7000, rm9000, orion, sb1, vr4100, vr4111, vr4120, vr4300, vr5000, vr5400 and vr5500. The special value from-abi selects the most compatible architecture for the selected ABI (that is, mips1 for 32-bit ABIs and mips3 for 64-bit ABIs).

In processor names, a final 000 can be abbreviated as k (for example, -march=r2k). Prefixes are optional, and vr may be written r.

GCC defines two macros based on the value of this option. The first is _MIPS_ARCH, which gives the name of target architecture, as a string. The second has the form _MIPS_ARCH_foo, where foo is the capitalized value of _MIPS_ARCH. For example, -march=r2000 will set _MIPS_ARCH to "r2000" and define the macro _MIPS_ARCH_R2000.

Note that the _MIPS_ARCH macro uses the processor names given above. In other words, it will have the full prefix and will not abbreviate 000 as k. In the case of from-abi, the macro names the resolved architecture (either "mips1" or "mips3"). It names the default architecture when no -march option is given.

-mtune=arch

Optimize for arch. Among other things, this option controls the way instructions are scheduled, and the perceived cost of arithmetic operations. The list of arch values is the same as for -march.

When this option is not used, GCC will optimize for the processor specified by -march. By using -march and -mtune together, it is possible to generate code that will run on a family of processors, but optimize the code for one particular member of that family.

-mtune defines the macros _MIPS_TUNE and _MIPS_TUNE_foo, which work in the same way as the -march ones described above.

-mips1

Equivalent to -march=mips1.

-mips2

Equivalent to -march=mips2.

-mips3

Equivalent to -march=mips3.

-mips4

Equivalent to -march=mips4.

-mips32

Equivalent to -march=mips32.

-mips32r2

Equivalent to -march=mips32r2.

-mips64

Equivalent to -march=mips64.

-mips16

-mno-mips16

Use (do not use) the MIPS16 ISA.

-mabi=32

-mabi=o64

-mabi=n32

-mabi=64

-mabi=eabi

Generate code for the given ABI.

Note that the EABI has a 32-bit and a 64-bit variant. GCC normally generates 64-bit code when you select a 64-bit architecture, but you can use -mgp32 to get 32-bit code instead.

-mabicalls

-mno-abicalls

Generate (do not generate) SVR4-style position-independent code. -mabicalls is the default for SVR4-based systems.

-mxgot

-mno-xgot

Lift (do not lift) the usual restrictions on the size of the global offset table.

GCC normally uses a single instruction to load values from the GOT. While this is relatively efficient, it will only work if the GOT is smaller than about 64k. Anything larger will cause the linker to report an error such as:

          relocation truncated to fit: R_MIPS_GOT16 foobar
     

If this happens, you should recompile your code with -mxgot. It should then work with very large GOTs, although it will also be less efficient, since it will take three instructions to fetch the value of a global symbol.

Note that some linkers can create multiple GOTs. If you have such a linker, you should only need to use -mxgot when a single object file accesses more than 64k's worth of GOT entries. Very few do.

These options have no effect unless GCC is generating position independent code.

-membedded-pic

-mno-embedded-pic

Generate (do not generate) position-independent code suitable for some embedded systems. All calls are made using PC relative addresses, and all data is addressed using the $gp register. No more than 65536 bytes of global data may be used. This requires GNU as and GNU ld, which do most of the work.

-mgp32

Assume that general-purpose registers are 32 bits wide.

-mgp64

Assume that general-purpose registers are 64 bits wide.

-mfp32

Assume that floating-point registers are 32 bits wide.

-mfp64

Assume that floating-point registers are 64 bits wide.

-mhard-float

Use floating-point coprocessor instructions.

-msoft-float

Do not use floating-point coprocessor instructions. Implement floating-point calculations using library calls instead.

-msingle-float

Assume that the floating-point coprocessor only supports single-precision operations.

-mdouble-float

Assume that the floating-point coprocessor supports double-precision operations. This is the default.

-mint64

Force int and long types to be 64 bits wide. See -mlong32 for an explanation of the default and the way that the pointer size is determined.

-mlong64

Force long types to be 64 bits wide. See -mlong32 for an explanation of the default and the way that the pointer size is determined.

-mlong32

Force long, int, and pointer types to be 32 bits wide.

The default size of ints, longs and pointers depends on the ABI. All the supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as does the 64-bit EABI; the others use 32-bit longs. Pointers are the same size as longs, or the same size as integer registers, whichever is smaller.

-G num

Put global and static items less than or equal to num bytes into the small data or bss section instead of the normal data or bss section. This allows the data to be accessed using a single instruction.

All modules should be compiled with the same -G num value.

-membedded-data

-mno-embedded-data

Allocate variables to the read-only data section first if possible, then next in the small data section if possible, otherwise in data. This gives slightly slower code than the default, but reduces the amount of RAM required when executing, and thus may be preferred for some embedded systems.

-muninit-const-in-rodata

-mno-uninit-const-in-rodata

Put uninitialized const variables in the read-only data section. This option is only meaningful in conjunction with -membedded-data.

-msplit-addresses

-mno-split-addresses

Enable (disable) use of the %hi() and %lo() assembler relocation operators. This option has been superceded by -mexplicit-relocs but is retained for backwards compatibility.

-mexplicit-relocs

-mno-explicit-relocs

Use (do not use) assembler relocation operators when dealing with symbolic addresses. The alternative, selected by -mno-explicit-relocs, is to use assembler macros instead.

-mexplicit-relocs is usually the default if GCC was configured to use an assembler that supports relocation operators. However, there are two exceptions:

• GCC is not yet able to generate explicit relocations for the combination of -mabi=64 and -mno-abicalls. This will be addressed in a future release.
• The combination of -mabicalls and -fno-unit-at-a-time implies -mno-explicit-relocs unless explicitly overridden. This is because, when generating abicalls, the choice of relocation depends on whether a symbol is local or global. In some rare cases, GCC will not be able to decide this until the whole compilation unit has been read.

-mrnames

-mno-rnames

Generate (do not generate) code that refers to registers using their software names. The default is -mno-rnames, which tells GCC to use hardware names like $4 instead of software names like a0. The only assembler known to support -rnames is the Algorithmics assembler.

-mcheck-zero-division

-mno-check-zero-division

Trap (do not trap) on integer division by zero. The default is -mcheck-zero-division.

-mmemcpy

-mno-memcpy

Force (do not force) the use of memcpy() for non-trivial block moves. The default is -mno-memcpy, which allows GCC to inline most constant-sized copies.

-mlong-calls

-mno-long-calls

Disable (do not disable) use of the jal instruction. Calling functions using jal is more efficient but requires the caller and callee to be in the same 256 megabyte segment.

This option has no effect on abicalls code. The default is -mno-long-calls.

-mmad

-mno-mad

Enable (disable) use of the mad, madu and mul instructions, as provided by the R4650 ISA.

-mfused-madd

-mno-fused-madd

Enable (disable) use of the floating point multiply-accumulate instructions, when they are available. The default is -mfused-madd.

When multiply-accumulate instructions are used, the intermediate product is calculated to infinite precision and is not subject to the FCSR Flush to Zero bit. This may be undesirable in some circumstances.

-nocpp

Tell the MIPS assembler to not run its preprocessor over user assembler files (with a .s suffix) when assembling them.

-mfix-sb1

-mno-fix-sb1

Work around certain SB-1 CPU core errata. (This flag currently works around the SB-1 revision 2 “F1” and “F2” floating point errata.)

-mflush-func=func

-mno-flush-func

Specifies the function to call to flush the I and D caches, or to not call any such function. If called, the function must take the same arguments as the common _flush_func(), that is, the address of the memory range for which the cache is being flushed, the size of the memory range, and the number 3 (to flush both caches). The default depends on the target GCC was configured for, but commonly is either _flush_func or __cpu_flush.

-mbranch-likely

-mno-branch-likely

Enable or disable use of Branch Likely instructions, regardless of the default for the selected architecture. By default, Branch Likely instructions may be generated if they are supported by the selected architecture. An exception is for the MIPS32 and MIPS64 architectures and processors which implement those architectures; for those, Branch Likely instructions will not be generated by default because the MIPS32 and MIPS64 architectures specifically deprecate their use.