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3.18.37 RISC-V Options

These command-line options are defined for RISC-V targets:

-mbranch-cost=n

Set the cost of branches to roughly n instructions.

-mplt
-mno-plt

When generating PIC code, do or don’t allow the use of PLTs. Ignored for non-PIC. The default is -mplt.

-mabi=ABI-string

Specify integer and floating-point calling convention. ABI-string contains two parts: the size of integer types and the registers used for floating-point types. For example ‘-march=rv64ifd -mabi=lp64d’ means that ‘long’ and pointers are 64-bit (implicitly defining ‘int’ to be 32-bit), and that floating-point values up to 64 bits wide are passed in F registers. Contrast this with ‘-march=rv64ifd -mabi=lp64f’, which still allows the compiler to generate code that uses the F and D extensions but only allows floating-point values up to 32 bits long to be passed in registers; or ‘-march=rv64ifd -mabi=lp64’, in which no floating-point arguments will be passed in registers.

The default for this argument is system dependent, users who want a specific calling convention should specify one explicitly. The valid calling conventions are: ‘ilp32’, ‘ilp32f’, ‘ilp32d’, ‘lp64’, ‘lp64f’, and ‘lp64d’. Some calling conventions are impossible to implement on some ISAs: for example, ‘-march=rv32if -mabi=ilp32d’ is invalid because the ABI requires 64-bit values be passed in F registers, but F registers are only 32 bits wide.

-mfdiv
-mno-fdiv

Do or don’t use hardware floating-point divide and square root instructions. This requires the F or D extensions for floating-point registers. The default is to use them if the specified architecture has these instructions.

-mdiv
-mno-div

Do or don’t use hardware instructions for integer division. This requires the M extension. The default is to use them if the specified architecture has these instructions.

-march=ISA-string

Generate code for given RISC-V ISA (e.g. ‘rv64im’). ISA strings must be lower-case. Examples include ‘rv64i’, ‘rv32g’, and ‘rv32imaf’.

-mtune=processor-string

Optimize the output for the given processor, specified by microarchitecture name.

-mpreferred-stack-boundary=num

Attempt to keep the stack boundary aligned to a 2 raised to num byte boundary. If -mpreferred-stack-boundary is not specified, the default is 4 (16 bytes or 128-bits).

Warning: If you use this switch, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules.

-msmall-data-limit=n

Put global and static data smaller than n bytes into a special section (on some targets).

-msave-restore
-mno-save-restore

Do or don’t use smaller but slower prologue and epilogue code that uses library function calls. The default is to use fast inline prologues and epilogues.

-mstrict-align
-mno-strict-align

Do not or do generate unaligned memory accesses. The default is set depending on whether the processor we are optimizing for supports fast unaligned access or not.

-mcmodel=medlow

Generate code for the medium-low code model. The program and its statically defined symbols must lie within a single 2 GiB address range and must lie between absolute addresses -2 GiB and +2 GiB. Programs can be statically or dynamically linked. This is the default code model.

-mcmodel=medany

Generate code for the medium-any code model. The program and its statically defined symbols must be within any single 2 GiB address range. Programs can be statically or dynamically linked.

-mexplicit-relocs
-mno-exlicit-relocs

Use or do not use assembler relocation operators when dealing with symbolic addresses. The alternative is to use assembler macros instead, which may limit optimization.


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