Cross Compiling

[freetoair]

Hi

How to compile for an ARM machine on a Linux host ?

[vvaltchev]

Hi @freetoair,
I converted this to a discussion, since it's not a bug.
tfblib is a fairly simple C library and can be cross-compiled like any other CMake project.
Check this out: https://cmake.org/cmake/help/book/mastering-cmake/chapter/Cross%20Compiling%20With%20CMake.html

In summary, you need to create a "toolchain file" for CMake and call cmake like this:

cmake -DCMAKE_TOOLCHAIN_FILE=otherToolchainFile.cmake

The bare minimum things a toolchain file needs is the paths for the compiler and potentially other basic tools. Here's an example from another project of mine:

      set(CMAKE_C_COMPILER ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-gcc)
      set(CMAKE_CXX_COMPILER ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-g++)
      set(CMAKE_ASM_COMPILER ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-gcc)
      set(CMAKE_OBJCOPY ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-objcopy)
      set(CMAKE_STRIP ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-strip)
      set(CMAKE_AR ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-ar)
      set(CMAKE_RANLIB ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-ranlib)

You can download and pre-built cross toolchain for many architectures here: https://toolchains.bootlin.com/
The host machine is assumed to be x86_64.

Vlad

[freetoair]

Hi, Vladislav

Yes, that's exactly what I did:

# the name of the target operating system
set(CMAKE_SYSTEM_NAME luckfoxpico)

# which compilers to use for C and C++
set(CMAKE_C_COMPILER   /home/luckfox-pico/tools/linux/toolchain/arm-rockchip830-linux-uclibcgnueabihf/bin/arm-rockchip830-linux-uclibcgnueabihf-gcc)
set(CMAKE_CXX_COMPILER /home/luckfox-pico/tools/linux/toolchain/arm-rockchip830-linux-uclibcgnueabihf/bin/arm-rockchip830-linux-uclibcgnueabihf-g++)

# where is the target environment located
set(CMAKE_FIND_ROOT_PATH   )

# adjust the default behavior of the FIND_XXX() commands:
# search programs in the host environment
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)

# search headers and libraries in the target environment
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

according to the instructions from the cmake website
compilation is successful, but I can't find the output files:
tfblib.h
etc...

[freetoair]

I compiled with make VERBOSE=1, so I'm pretty sure the proper tool was used !

[vvaltchev]

@freetoair You're setting a bunch of things that might have undesired effects and you're NOT setting AR and RANLIB, which you should set. Start setting the following:

set(GCC_TOOLCHAIN "/home/vlad/dev/tilck_toolchains/host_x86_64/gcc_12_3_0_riscv64_musl/bin")
set(ARCH_GCC_TC "riscv64")


set(CMAKE_C_COMPILER ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-gcc)
set(CMAKE_CXX_COMPILER ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-g++)
set(CMAKE_ASM_COMPILER ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-gcc)
set(CMAKE_AR ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-ar)
set(CMAKE_RANLIB ${GCC_TOOLCHAIN}/${ARCH_GCC_TC}-linux-ranlib)

I just tried exactly that with a RISCV64 toolchain from https://toolchains.bootlin.com/.

Full instructions:

0. enter in project's directory and create the toolchain.cmake file
1. mkdir build/
2. cd build/
3. cmake -DCMAKE_TOOLCHAIN_FILE=<yourJustCreatedToolchain.cmake> ..
4. make

You'll see libtfb.a in the build directory. That's the library, statically linked.

[freetoair]

HI Vladislav,

First, thank you for your effort and time to answer.
Everything is fine now, all the files appeared. Just one more question: Where should libtfb.a be in the file system?
When I try to run one of the examples I keep getting the message:

root@luckfox:~# ls
fb_tetris  libtfb.a
root@luckfox:~# ./fb_tetris
-bash: ./fb_tetris: No such file or directory
root@luckfox:~#

Problem may be in my embedded system for some reason. but I'm thinking if libtfb.a should be in PATH in .bashrc . Otherwise fb_tetris file has allowed execute mode.

[vvaltchev]

@freetoair, a static library is located nowhere on the target system. It is linked inside the executable. That's a very basic concept. The library file is visible in the build directory so that you can link it in your own application, outside of the "tfblib" project, but the examples like fb_tetris are already linked with it.

I hope you don't expect me to teach you everything there is to know about compiling & linking. It wouldn't be a fair ask. The amount of things to learn there is very significant. A good book about the topic is: "Linkers and Loaders" by John R. Levine. Another book is "Advanced C and C++ Compiling", to read after that one.

The error you see:

-bash: ./fb_tetris: No such file or directory

Is shown also when the binary is not compiled for the current architecture. "ARM" is not a specific target architecture, but a family of architectures instead. There are many flavors and versions of "ARM", even just the 32-bit version. On https://toolchains.bootlin.com/ they have:

• aarch64
• aarch64be
• armebv7-eabihf
• armv5-eabi
• armv6-eabihf
• armv7-eabihf
• armv7m

And that list is NOT exhaustive. For sure you didn't pick up the right architecture, but I'm not going to help any further than that. You'd need to learn how to debug what's wrong by yourself. I know it's not easy, but that was the very best I could do for you.

Vlad