Overview

If you only want to run code on one particular processor, you can target that specific processor. Performance is optimized, but code is only guaranteed to run on that processor.

If you want your code to run on a wide range of processors, you can target an architecture. The code runs on any processor implementation of the target architecture, but performance might be impacted.

The options for specifying a target are as follows:

1. Specify the execution state using the --target option.

   The execution state can be AArch64 or AArch32 depending on the processor.

2. Target one of the following:

   • an architecture using the -march option.
   • a specific processor using the -mcpu option.
3. (AArch32 targets only) Specify the floating-point hardware available using the -mfpu option, or omit to use the default for the target.
4. (AArch32 targets only) For processors that support both A32 (formerly ARM) and T32 (formerly Thumb) instruction sets, specify the instruction set using -marm or -mthumb, or omit to default to -marm.

Specifying the target execution state

To specify a target execution state with armclang, use the --target command-line option:

--target=arch-vendor-os-abi

Supported targets are as follows:

aarch64-arm-none-eabi

Generates A64 instructions for AArch64 state. Implies -march=armv8-a unless -mcpu is specified.

arm-arm-none-eabi

Generates A32/T32 instructions for AArch32 state. Must be used in conjunction with -march (to target an architecture) or -mcpu (to target a processor).

Specifying the target architecture

Targeting an architecture with --target and -march generates generic code that runs on any processor with that architecture.

Use the -march=list option to see all supported architectures.

Specifying a particular processor

Targeting a processor with --target and -mcpu optimizes code for the specified processor.

Use the -mcpu=list option to see all supported processors.

You can specify feature modifiers with -mcpu and -march. For example -mcpu=cortex-a57+nocrypto.

Specifying the floating-point hardware available on the target

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

Specifying the instruction set

Different architectures support different instruction sets:

• Armv8‑A processors in AArch64 state execute A64 instructions.
• Armv8‑A processors in AArch32 state, as well as Armv7 and earlier A- and R- profile processors execute A32 and T32 instructions.
• M-profile processors execute T32 instructions.

To specify the target instruction set, use the following command-line options:

• -marm targets the A32 instruction set. This is the default for all targets that support A32 instructions.
• -mthumb targets the T32 instruction set. This is the default for all targets that only support T32 instructions.

Command-line examples

The following examples show how to compile for different combinations of architecture, processor, and instruction set: