"./asm_offset: Exec format error" when building for arm64

[kexia01]

I want to build loader for arm64,
set(CMAKE_SYSTEM_PROCESSOR "aarch64") in loader/CMakeList.txt
and export CC/CXX.
export CC=aarch64-linux-gnu-gcc
export CXX=aarch64-linux-gnu-g++

Then, build as the following command:
mkdir build
cd build
../scripts/update_deps.py
cmake -C helper.cmake ..
cmake --build .

Log for cmake -C:
-- Check for working C compiler: /tools/gcc_aarch64/4.9_2014.07/bin/aarch64-linux-gnu-gcc
-- Check for working CXX compiler: /tools/gcc_aarch64/4.9_2014.07/bin/aarch64-linux-gnu-gcc
-- The ASM compiler identification is GNU
-- Found assembler: /tools/gcc_aarch64/4.9_2014.07/bin/aarch64-linux-gnu-gcc

Error for build:
k01@a01-lin:~/work/source/Vulkan-Loader/build$ cmake --build .
Scanning dependencies of target asm_offset
[ 5%] Building C object loader/CMakeFiles/asm_offset.dir/asm_offset.c.o
[ 10%] Linking C executable asm_offset
[ 10%] Built target asm_offset
Scanning dependencies of target loader_asm_gen_files
[ 15%] Generating gen_defines.asm
/bin/sh: 1: ./asm_offset: Exec format error
loader/CMakeFiles/loader_asm_gen_files.dir/build.make:79: recipe for target 'loader/gen_defines.asm' failed
make[2]: *** [loader/gen_defines.asm] Error 2
CMakeFiles/Makefile2:171: recipe for target 'loader/CMakeFiles/loader_asm_gen_files.dir/all' failed
make[1]: *** [loader/CMakeFiles/loader_asm_gen_files.dir/all] Error 2
Makefile:148: recipe for target 'all' failed
make: *** [all] Error 2

[kexia01]

If export asm:
export ASM=aarch64-linux-gnu-as

-- The ASM compiler identification is GNU
-- Found assembler: /tools/gcc_aarch64/4.9_2014.07/bin/aarch64-linux-gnu-as

Building error is the same.

[jyangsh]

looks the change is introduced by PR #731 . @esullivan-nvidia

[SupervisedThinking]

Is your buildsystem aarch64 too? If not you need to build a x86 asm_offset binary first & reuse it for the aarch64 build...

[Mindavi]

Running into this within nixpkgs as well. This is what the cmake boot/manual recommends doing: https://cmake.org/cmake/help/book/mastering-cmake/chapter/Cross%20Compiling%20With%20CMake.html#running-executables-built-in-the-project

Kinda makes me sad to have to deal with that, but I guess it's kinda inevitable since cmake doesn't support compiling for build and target system in one go.

NixOS/nixpkgs#170366 (comment)

Trying to cross-compile from x86_64 to aarch64.

Gonna try setting -DUSE_GAS=OFF, but I'm not sure what the implications are there. I saw some warnings about tail-call optimization being mandatory or so?

[charles-lunarg]

This appears to be the same as #249 as the issue is that cross-compilation is not support supported due to asm_offset needing to be run. /bin/sh: 1: ./asm_offset: Exec format error indicates that cmake tries to run the built executable but fails to do so, thus failing to generate the gen_defines.asm file and failing the build.

This is a bug, and I am working on a fix for cross compilation that is discussed further in the linked issue.