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Compiler Reference Guide

Preface Arm Compiler Tools Overview armclang Reference armclang Command-line Options Summary of armclang command-line options -C (armclang) -c (armclang) -D -E -e -fbare-metal-pie -fbracket-depth=N -fcommon, -fno-common -fdata-sections, -fno-data-sections -ffast-math, -fno-fast-math -ffixed-rN -ffp-mode -ffunction-sections, -fno-function-sections -fident, -fno-ident @file -fldm-stm, -fno-ldm-stm -fno-builtin -fno-inline-functions -flto, -fno-lto -fexceptions, -fno-exceptions -fomit-frame-pointer, -fno-omit-frame-pointer -fpic, -fno-pic -fropi, -fno-ropi -fropi-lowering, -fno-ropi-lowering -frwpi, -fno-rwpi -frwpi-lowering, -fno-rwpi-lowering -fsanitize -fshort-enums, -fno-short-enums -fshort-wchar, -fno-short-wchar -fstack-protector, -fstack-protector-all, -fstack- -fstrict-aliasing, -fno-strict-aliasing -fsysv, -fno-sysv -ftrapv -fvectorize, -fno-vectorize -fvisibility -fwrapv -g, -gdwarf-2, -gdwarf-3, -gdwarf-4 (armclang) -I -include -L -l -M, -MM -MD, -MMD -MF -MG -MP -MT -march -marm -masm -mbig-endian -mbranch-protection -mcmodel -mcmse -mcpu -mexecute-only -mfloat-abi -mfpu -mimplicit-it -mlittle-endian -mno-neg-immediates -moutline, -mno-outline -mpixolib -munaligned-access, -mno-unaligned-access -mthumb -nostdlib -nostdlibinc -o (armclang) -O (armclang) -pedantic -pedantic-errors -Rpass -S -save-temps -shared (armclang) -std --target -U -u (armclang) -v (armclang) --version (armclang) --version_number (armclang) --vsn (armclang) -W -Wl -Xlinker -x (armclang) -### Compiler-specific Keywords and Operators Compiler-specific keywords and operators __alignof__ __asm __declspec attributes __declspec(noinline) __declspec(noreturn) __declspec(nothrow) __inline __promise __unaligned Global named register variables Compiler-specific Function, Variable, and Type Att Function attributes __attribute__((always_inline)) function attribute __attribute__((cmse_nonsecure_call)) function attr __attribute__((cmse_nonsecure_entry)) function att __attribute__((const)) function attribute __attribute__((constructor(priority))) function at __attribute__((format_arg(string-index))) function __attribute__((interrupt("type"))) function attrib __attribute__((malloc)) function attribute __attribute__((naked)) function attribute __attribute__((noinline)) function attribute __attribute__((nonnull)) function attribute __attribute__((noreturn)) function attribute __attribute__((nothrow)) function attribute __attribute__((pcs("calling_convention"))) functio __attribute__((pure)) function attribute __attribute__((section("name"))) function attribut __attribute__((unused)) function attribute __attribute__((used)) function attribute __attribute__((value_in_regs)) function attribute __attribute__((visibility("visibility_type"))) fun __attribute__((weak)) function attribute __attribute__((weakref("target"))) function attrib Type attributes __attribute__((aligned)) type attribute __attribute__((packed)) type attribute __attribute__((transparent_union)) type attribute Variable attributes __attribute__((alias)) variable attribute __attribute__((aligned)) variable attribute __attribute__((deprecated)) variable attribute __attribute__((packed)) variable attribute __attribute__((section("name"))) variable attribut __attribute__((unused)) variable attribute __attribute__((used)) variable attribute __attribute__((visibility("visibility_type"))) var __attribute__((weak)) variable attribute __attribute__((weakref("target"))) variable attrib Compiler-specific Intrinsics __breakpoint intrinsic __current_pc intrinsic __current_sp intrinsic __disable_fiq intrinsic __disable_irq intrinsic __enable_fiq intrinsic __enable_irq intrinsic __force_stores intrinsic __memory_changed intrinsic __schedule_barrier intrinsic __semihost intrinsic __vfp_status intrinsic Compiler-specific Pragmas #pragma clang system_header #pragma clang diagnostic #pragma clang section #pragma once #pragma pack(...) #pragma unroll[(n)], #pragma unroll_completely #pragma weak symbol, #pragma weak symbol1 = symbol Other Compiler-specific Features ACLE support Predefined macros Inline functions Half-precision floating-point data types Half-precision floating-point number format Half-precision floating-point intrinsics Library support for _Float16 data type BFloat16 floating-point number format TT instruction intrinsics Non-secure function pointer intrinsics armclang Integrated Assembler Syntax of assembly files for integrated assembler Assembly expressions Alignment directives Data definition directives String definition directives Floating-point data definition directives Section directives Conditional assembly directives Macro directives Symbol binding directives Org directive AArch32 Target selection directives AArch64 Target selection directives Space-filling directives Type directive Integrated assembler support for the CSDB instruct armclang Inline Assembler Inline Assembly File-scope inline assembly Inline assembly statements within a function Assembly string Output and input operands Clobber list volatile Inline assembly constraint strings Constraint modifiers Constraint codes Constraint codes common to AArch32 state and AArch Constraint codes for AArch32 state Constraint codes for AArch64 state Using multiple alternative operand constraints Inline assembly template modifiers Template modifiers common to AArch32 state and AAr Template modifiers for AArch32 state Template modifiers for AArch64 state Forcing inline assembly operands into specific reg Symbol references and branches into and out of inl Duplication of labels in inline assembly statement armlink Reference fromelf Reference armar Reference armasm Legacy Assembler Reference Appendixes

-mfpu

B1.59 -mfpu

Specifies the target FPU architecture, that is the floating-point hardware available on the target.

Syntax

To view a list of all the supported FPU architectures, use:

-mfpu=list

Note:

-mfpu=list is rejected when targeting AArch64 state.

Alternatively, to specify a target FPU architecture, use:

-mfpu=name

Where name is one of the following:

none
Prevents the compiler from using hardware-based floating-point functions. If the compiler encounters floating-point types in the source code, it uses software-based floating-point library functions. This is similar to the -mfloat-abi=soft option.
vfpv3
Enable the Arm®v7 VFPv3 floating-point extension. Disable the Advanced SIMD extension.
vfpv3-d16
Enable the Armv7 VFPv3-D16 floating-point extension. Disable the Advanced SIMD extension.
vfpv3-fp16
Enable the Armv7 VFPv3 floating-point extension, including the optional half-precision extensions. Disable the Advanced SIMD extension.
vfpv3-d16-fp16
Enable the Armv7 VFPv3-D16 floating-point extension, including the optional half-precision extensions. Disable the Advanced SIMD extension.
vfpv3xd
Enable the Armv7 VFPv3XD floating-point extension. Disable the Advanced SIMD extension.
vfpv3xd-fp16
Enable the Armv7 VFPv3XD floating-point extension, including the optional half-precision extensions. Disable the Advanced SIMD extension.
neon
Enable the Armv7 VFPv3 floating-point extension and the Advanced SIMD extension.
neon-fp16
Enable the Armv7 VFPv3 floating-point extension, including the optional half-precision extensions, and the Advanced SIMD extension.
vfpv4
Enable the Armv7 VFPv4 floating-point extension. Disable the Advanced SIMD extension.
vfpv4-d16
Enable the Armv7 VFPv4-D16 floating-point extension. Disable the Advanced SIMD extension.
neon-vfpv4
Enable the Armv7 VFPv4 floating-point extension and the Advanced SIMD extension.
fpv4-sp-d16
Enable the Armv7 FPv4-SP-D16 floating-point extension.
fpv5-d16
Enable the Armv7 FPv5-D16 floating-point extension.
fpv5-sp-d16
Enable the Armv7 FPv5-SP-D16 floating-point extension.
fp-armv8
Enable the Armv8 floating-point extension. Disable the cryptographic extension and the Advanced SIMD extension.
neon-fp-armv8
Enable the Armv8 floating-point extension and the Advanced SIMD extensions. Disable the cryptographic extension.
crypto-neon-fp-armv8
Enable the Armv8 floating-point extension, the cryptographic extension, and the Advanced SIMD extension.

The -mfpu option overrides the default FPU option implied by the target architecture.

Note:

  • The -mfpu option is ignored with AArch64 targets, for example aarch64-arm-none-eabi. Use the -mcpu option to override the default FPU for aarch64-arm-none-eabi targets. For example, to prevent the use of floating-point instructions or floating-point registers for the aarch64-arm-none-eabi target use the -mcpu=name+nofp+nosimd option. Subsequent use of floating-point data types in this mode is unsupported.
  • In Armv7, the Advanced SIMD extension was called the Arm Neon™ Advanced SIMD extension.

Note:

There are no software floating-point libraries for targets in AArch64 state. When linking for targets in AArch64 state, armlink uses AArch64 libraries that contain Advanced SIMD and floating-point instructions and registers. The use of the AArch64 libraries applies even if you compile the source with -mcpu=<name>+nofp+nosimd to prevent the compiler from using Advanced SIMD and floating-point instructions and registers. Therefore, there is no guarantee that the linked image for targets in AArch64 state is entirely free of Advanced SIMD and floating-point instructions and registers.

You can prevent the use of Advanced SIMD and floating-point instructions and registers in images that are linked for targets in AArch64 state. Either re-implement the library functions or create your own library that does not use Advanced SIMD and floating-point instructions and registers.

Note:

In AArch32 state, if you specify -mfloat-abi=soft, then specifying the -mfpu option does not have an effect.

Default

The default FPU option depends on the target processor.

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