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-mthumb

Requests that the compiler targets the T32 or Thumb® instruction sets.

Most ARMv7-A (and earlier) processors support two instruction sets: the ARM instruction set, and the Thumb instruction set. ARMv8-A AArch32 continues to support these two instruction sets, but they are renamed as A32 and T32 respectively. ARMv8-A additionally introduces the A64 instruction set, used in the AArch64 execution state.

Different architectures support different instruction sets:

  • ARMv8-A processors in AArch64 state execute A64 instructions.
  • ARMv8-A processors in AArch32 state, in addition to ARMv7 and earlier A- and R- profile processors execute A32 (formerly ARM) and T32 (formerly Thumb) instructions.
  • M-profile processors execute T32 (formerly Thumb) instructions.

The -mthumb option targets the T32 (formerly Thumb) instruction set.

Note

The -mthumb option is not valid with AArch64 targets, for example --target=aarch64-arm-none-eabi. The compiler ignores the -mthumb option and generates a warning with AArch64 targets.

Default

The default for all targets that support ARM or A32 instructions is -marm.

Example

armclang -c --target=arm-arm-none-eabi -march=armv8-a -mthumb test.c

Related reference

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