cmake : Set environment variables from a script

Question

I have a script that sets all variables needed for the cross-compilation. Here is just part of it :

export CONFIG_SITE=~/workspace/eldk-5.4/powerpc/site-config-powerpc-linux
export CC="powerpc-linux-gcc  -m32 -mhard-float --sysroot=~/workspace/eldk-5.4/powerpc/sysroots/powerpc-linux"
export CXX="powerpc-linux-g++  -m32 -mhard-float --sysroot=~/workspace/eldk-5.4/powerpc/sysroots/powerpc-linux"
export CPP="powerpc-linux-gcc -E  -m32 -mhard-float --sysroot=~/workspace/eldk-5.4/powerpc/sysroots/powerpc-linux"
export AS="powerpc-linux-as "
export LD="powerpc-linux-ld  --sysroot=~/workspace/eldk-5.4/powerpc/sysroots/powerpc-linux"
export GDB=powerpc-linux-gdb

If I do source environment-setup-powerpc-linux, all environment variables are imported into the current shell session, and I can compile my example.

Is it possible to import these variables in cmake? If yes, how?

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A bit more details :

1. I am using ELDK v 5.4, and it's install script generates a script which sets all environment variables
2. I found this tutorial, which explains how to manually set for cross-compilation, but not how to use the script, which sets everything
3. if I call the script before setting cmake, all works fine, and I can cross-compile, but I'd like that cmake calls the script

Answer 1

Reading through the cmake quick start, you can specify variable on a command line:

cmake -DVARIABLE1=value1 -DVARIABLE2=value2 ...

Otherwise, set command in the cmake script is probably what you want, see the reference manual. To set the environment variable PATH, do:

set(ENV{PATH} "/home/martink")

To set normal variable, do:

set(variable "value")

Not sure which ones you have to set, probably the environment ones.

That said, setting environment variable prior to calling cmake is often the easiest solution to solve the problem, as in this case: https://stackoverflow.com/a/15053460/684229

Answer 2

The only way to set a compiler and flags to do cross-compilation reliably with CMake is with a toolchain-file as done in the tutorial you have found.

When we faced the same issue you have (a toolkit which produces a script so set the compile-environment) we changed the toolkit in a way that it produces a toolchain-file along with the script.

In reality a cmake-toolchain-file does not change that often. The basic flags used for the target are fixed quite early in a project - normally. And with CMake's CMAKE_BUILD_TYPE you can switch between Debug and Release compilations without changing the toolchain-file.

If you have different targets to support, create different toolchain and use the out-of-source-build with CMake.

EDIT: One thing you could do is to invoke cmake with the -D-argument setting the variables you want to and having sourced your script before:

source environment-setup-powerpc-linux
cmake -DCMAKE_C_COMPILER=$CC -DCMAKE_CXX_COMPILER=$CXX etc

The result will be identical as to having used a toolchain-file.