[cmake-developers] CMAKE_INSTALL_PREFIX vs CMAKE_SYSROOT ?

[Stephen Kelly]

Hi there,

Given a generic toolchain file like this:

 
 set(CMAKE_SYSTEM_NAME Linux)

 set(CMAKE_C_COMPILER "arm-linux-gnueabihf-gcc")
 set(CMAKE_CXX_COMPILER "arm-linux-gnueabihf-g++")

 set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
 set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)


I can invoke cmake like this:

 cmake .. -DCMAKE_TOOLCHAIN_FILE=../ArmToolchain.cmake \
  -DCMAKE_SYSROOT=/home/stephen/rpi/rasp-pi-rootfs/ \
  -DCMAKE_MAKE_PROGRAM=/usr/bin/make \
  -DCMAKE_INSTALL_PREFIX=/opt/myproject


Question: Should the installation be to 

 /opt/myproject 

on the host, or to 

 /home/stephen/rpi/rasp-pi-rootfs/opt/myproject

on the host?

For the Qt configure, the answer is the latter, and I think it makes sense. 
As CMAKE_SYSROOT is new, we can still change the behavior to that. I tend to 
think we should.

However, that leaves the question of how to install outside the sysroot. An 
option would be something like a new CMAKE_HOST_INSTALL_PREFIX:

 cmake .. -DCMAKE_TOOLCHAIN_FILE=../ArmToolchain.cmake \
  -DCMAKE_SYSROOT=/home/stephen/rpi/rasp-pi-rootfs/ \
  -DCMAKE_MAKE_PROGRAM=/usr/bin/make \
  -DCMAKE_HOST_INSTALL_PREFIX=/opt/myproject

which installs to 

 /opt/myproject

on the host.

This is the subject of a patch to Qt:

 https://codereview.qt-project.org/#change,59009

This is useful because I've done embedded development where I created an NFS 
mount in the host and mounted it in the target. Then I can make install on 
the host and can quickly and easily use the result on the target, which 
still has correct RPATH information etc.

Comments?

Thanks,

Steve.