编译ARM时GCC错误

Question

I am getting the following error while trying to compile some code for an ARM Cortex-M4 using

gcc -mcpu=cortex-m4 arm.c  

`-mcpu=' is deprecated. Use `-mtune=' or '-march=' instead.
arm.c:1: error: bad value (cortex-m4) for -mtune= switch

I was following GCC 4.7.1 ARM options . Not sure whether I am missing some critical option. Any kickstart for using GCC for ARM will also be really helpful.

Answer 1

As starblue implied in a comment, that error is because you're using a native compiler built for compiling for x86 CPUs, rather than a cross-compiler for compiling to ARM.

GCC only supports a single general architecture type in any given compiler binary -- so, although the same copy of GCC can compile for both 32-bit and 64-bit x86 machines, you can't compile to both x86 and ARM with the same copy of GCC -- you need an ARM-specific GCC.

(As auselen suggests, getting a pre-built one will save you quite a lot of work, even if you're only using it as a starting point to get things set up. You need to have GCC, binutils, and a C library as a minimum, and those are all separate open-source projects that the pre-built versions have already done the work of combining. I'll recommend Sourcery CodeBench Lite since that's the one my company makes and I do think it's a fairly good one.)

Answer 2

As the error message says -mcpu is deprecated, and you should use the other options stated. However " deprectated " simply means that its use may not continue to be supported; it will still work.

ARM Cortex-M4 is ARM Architecture V7E-M, so you should use -march=armv7-m (the documentation does not specifically list armv7e-m , but that may have been added since the documentation was last updated. The E is essentially the difference between M3 and M4 - the DSP instructions, so the compiler will not generate code that takes advantage of these instructions. Using ARM's Cortex-M DSP library is probably the best way to use these instructions to benefit your application. If your part has an FPU, then other options will be needed enable code generation for that.

Answer 3

Like others already pointed out, you are using a compiler for your host machine, and you need a compiler for generating code for your target processor instead (a cross compiler). Like @Brooks suggested, you can use a pre-built toolchain, but if you want to roll out your own cross-compiler, libc and binutils, there is a nice tool called Crosstool-NG . It greatly simplifies the process of building a cross-compiler optimized to generate code for a specific processor, so you're not stuck with a generic prebuilt toolchain, which usually builds code for a family of compatible processors (eg you could tune the toolchain for generating ASM for your specific target, or floating point code for a hardware FPU which is specific to your processor, instead of using only software floating point routines, which are default to most pre-built toolchains).