[question] Force cross compilation

[upsilona]

Hello everyone,
I have a question regarding the cross compilation detection in conan. Reading the code I saw we assume cross compilation is enabled if os and / or arch is different between host and build. I managed to embed a Linux SDK for several targets archs into a conan package of my own. However I face compilation issues for x86 / x86_64 because of missing compilation flags, due to conan not detecting my cross compilation scenario. I was wondering if we shouldn't add an environment variable to force cross compilation, for instance CONAN_CROSS_COMPILATION.
NB : The code I build using my SDK is not intended to run on the build machine. I updated my conan settings to ensure all the dependencies get build using my SDK, avoiding contamination.
Regards

[ericLemanissier]

isn't this covered by the skip_x64_x86=True argument of tools.cross_building() ?

[SSE4]

I think it doesn't scale on recipe basis. perhaps, global override via conf or env var is required?
my guess is you may have an ARM Linux laptop and cross-compile for ARM board such as raspberry pi.
in this case conan won't detect cross-building (as both os and arch are the same), but actually it is.
same for x86 Linux desktop compiling for x86 board such as hackboard.
I think it's worth opening an issue for the conan client itself: https://github.com/conan-io/conan/issues/new/choose
(please try to desribe as much details as possible)

[jgsogo]

I'm moving this issue to Conan client repository. Right now cross-compilation is detected, but it might be worth being able to force it with some input.

[steinerthomas]

Hi,
what's the status? Will there be a flag for forcing cross building in the future?

I'm facing an issue "cross-building" from x86_64 Debian10 (build server, default profile) to x86_64 Debian12 (target) when building the benchmark library:

$conan create recipes/benchmark/all benchmark/1.8.2@ -u -tf None -pr debian6412 -pr:b default -s:b build_type=RelWithDebInfo -s build_type=RelWithDebInfo

ERROR:

-- Performing Test HAVE_POSIX_REGEX -- compiled but failed to run
CMake Error at CMakeLists.txt:299 (message):
  Failed to determine the source files for the regular expression backend

Full log

Exporting package recipe
benchmark/1.8.2 exports: File 'conandata.yml' found. Exporting it...
benchmark/1.8.2 exports: Copied 1 '.yml' file: conandata.yml
benchmark/1.8.2: The stored package has not changed
benchmark/1.8.2: Using the exported files summary hash as the recipe revision: 33859562c342e2d8e0a17918c1190fa2
benchmark/1.8.2: Exported revision: 33859562c342e2d8e0a17918c1190fa2
Configuration (profile_host):
[settings]
arch=x86_64
build_type=RelWithDebInfo
compiler=gcc
compiler.cppstd=20
compiler.libcxx=libstdc++11
compiler.version=12
os=Linux
[options]
[build_requires]
[env]
AR=x86_64-debian6412-linux-gnu-ar
AS=x86_64-debian6412-linux-gnu-as
CC=x86_64-debian6412-linux-gnu-gcc
CHOST=x86_64-debian6412-linux-gnu
CONAN_CMAKE_FIND_ROOT_PATH=/opt/x-tools/x86_64-debian6412-linux-gnu/x86_64-debian6412-linux-gnu/sysroot
CONAN_CMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY
CONAN_CMAKE_FIND_ROOT_PATH_MODE_LIBRARY=ONLY
CONAN_CMAKE_FIND_ROOT_PATH_MODE_PROGRAM=NEVER
CONAN_CMAKE_TOOLCHAIN_FILE=/opt/x-tools/x86_64-debian6412-linux-gnu/toolchain.cmake
CXX=x86_64-debian6412-linux-gnu-g++
LD=x86_64-debian6412-linux-gnu-ld
PATH=[/opt/x-tools/x86_64-debian6412-linux-gnu/bin]
RANLIB=x86_64-debian6412-linux-gnu-ranlib
STRIP=x86_64-debian6412-linux-gnu-strip
Configuration (profile_build):
[settings]
arch=x86_64
arch_build=x86_64
build_type=RelWithDebInfo
compiler=gcc
compiler.cppstd=17
compiler.libcxx=libstdc++11
compiler.version=8
os=Linux
os_build=Linux
[options]
[build_requires]
[env]

benchmark/1.8.2: Forced build from source
Version ranges solved
    cmake/* versions found in 'cc-conan-local' remote
    Version range '>=3.16.3 <4' required by 'benchmark/1.8.2' resolved to 'cmake/3.27.1' in remote 'cc-conan-local'

Installing package: benchmark/1.8.2
Requirements
    benchmark/1.8.2 from 'cc-conan-local' - Cache
Packages
    benchmark/1.8.2:e7f09c57b624b2100ef636844c070bdce803af28 - Build
Build requirements
    cmake/3.27.1 from 'cc-conan-local' - Cache
Build requirements packages
    cmake/3.27.1:4db1be536558d833e52e862fd84d64d75c2b3656 - Cache

Installing (downloading, building) binaries...
cmake/3.27.1: Already installed!
cmake/3.27.1: Appending PATH environment variable: /home/thomas/.conan/data/cmake/3.27.1/_/_/package/4db1be536558d833e52e862fd84d64d75c2b3656/bin
benchmark/1.8.2: Applying build-requirement: cmake/3.27.1
benchmark/1.8.2: WARN: Build folder is dirty, removing it: /home/thomas/.conan/data/benchmark/1.8.2/_/_/build/e7f09c57b624b2100ef636844c070bdce803af28
benchmark/1.8.2: Copying sources to build folder
benchmark/1.8.2: Building your package in /home/thomas/.conan/data/benchmark/1.8.2/_/_/build/e7f09c57b624b2100ef636844c070bdce803af28
benchmark/1.8.2: Generator txt created conanbuildinfo.txt
benchmark/1.8.2: Calling generate()
benchmark/1.8.2: Preset 'relwithdebinfo' added to CMakePresets.json. Invoke it manually using 'cmake --preset relwithdebinfo'
benchmark/1.8.2: If your CMake version is not compatible with CMakePresets (<3.19) call cmake like: 'cmake <path> -G "Unix Makefiles" -DCMAKE_TOOLCHAIN_FILE=/home/thomas/.conan/data/benchmark/1.8.2/_/_/build/e7f09c57b624b2100ef636844c070bdce803af28/build/RelWithDebInfo/generators/conan_toolchain.cmake -DCMAKE_POLICY_DEFAULT_CMP0091=NEW -DCMAKE_BUILD_TYPE=RelWithDebInfo'
benchmark/1.8.2: Aggregating env generators
benchmark/1.8.2: Calling build()
benchmark/1.8.2: CMake command: cmake -G "Unix Makefiles" -DCMAKE_TOOLCHAIN_FILE="/home/thomas/.conan/data/benchmark/1.8.2/_/_/build/e7f09c57b624b2100ef636844c070bdce803af28/build/RelWithDebInfo/generators/conan_toolchain.cmake" -DCMAKE_INSTALL_PREFIX="/home/thomas/.conan/data/benchmark/1.8.2/_/_/package/e7f09c57b624b2100ef636844c070bdce803af28" -DCMAKE_POLICY_DEFAULT_CMP0091="NEW" -DCMAKE_BUILD_TYPE="RelWithDebInfo" "/home/thomas/.conan/data/benchmark/1.8.2/_/_/build/e7f09c57b624b2100ef636844c070bdce803af28/src"
-- Using Conan toolchain: /home/thomas/.conan/data/benchmark/1.8.2/_/_/build/e7f09c57b624b2100ef636844c070bdce803af28/build/RelWithDebInfo/generators/conan_toolchain.cmake
-- Conan toolchain: Setting CMAKE_POSITION_INDEPENDENT_CODE=ON (options.fPIC)
-- Conan toolchain: C++ Standard 20 with extensions OFF
-- Conan toolchain: Setting BUILD_SHARED_LIBS = OFF
-- The CXX compiler identification is GNU 12.3.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /opt/x-tools/x86_64-debian6412-linux-gnu/bin/x86_64-debian6412-linux-gnu-g++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Failed to find LLVM FileCheck
-- Found Git: /usr/bin/git (found version "2.20.1")
-- git version: v0.0.0 normalized to 0.0.0
-- Google Benchmark version: 1.8.2
-- Looking for shm_open in rt
-- Looking for shm_open in rt - found
-- Performing Test HAVE_CXX_FLAG_WALL
-- Performing Test HAVE_CXX_FLAG_WALL - Success
-- Performing Test HAVE_CXX_FLAG_WEXTRA
-- Performing Test HAVE_CXX_FLAG_WEXTRA - Success
-- Performing Test HAVE_CXX_FLAG_WSHADOW
-- Performing Test HAVE_CXX_FLAG_WSHADOW - Success
-- Performing Test HAVE_CXX_FLAG_WFLOAT_EQUAL
-- Performing Test HAVE_CXX_FLAG_WFLOAT_EQUAL - Success
-- Performing Test HAVE_CXX_FLAG_WOLD_STYLE_CAST
-- Performing Test HAVE_CXX_FLAG_WOLD_STYLE_CAST - Success
-- Performing Test HAVE_CXX_FLAG_WSUGGEST_OVERRIDE
-- Performing Test HAVE_CXX_FLAG_WSUGGEST_OVERRIDE - Success
-- Performing Test HAVE_CXX_FLAG_PEDANTIC
-- Performing Test HAVE_CXX_FLAG_PEDANTIC - Success
-- Performing Test HAVE_CXX_FLAG_PEDANTIC_ERRORS
-- Performing Test HAVE_CXX_FLAG_PEDANTIC_ERRORS - Success
-- Performing Test HAVE_CXX_FLAG_WSHORTEN_64_TO_32
-- Performing Test HAVE_CXX_FLAG_WSHORTEN_64_TO_32 - Failed
-- Performing Test HAVE_CXX_FLAG_FSTRICT_ALIASING
-- Performing Test HAVE_CXX_FLAG_FSTRICT_ALIASING - Success
-- Performing Test HAVE_CXX_FLAG_WNO_DEPRECATED_DECLARATIONS
-- Performing Test HAVE_CXX_FLAG_WNO_DEPRECATED_DECLARATIONS - Success
-- Performing Test HAVE_CXX_FLAG_WSTRICT_ALIASING
-- Performing Test HAVE_CXX_FLAG_WSTRICT_ALIASING - Success
-- Performing Test HAVE_CXX_FLAG_WD654
-- Performing Test HAVE_CXX_FLAG_WD654 - Failed
-- Performing Test HAVE_CXX_FLAG_WTHREAD_SAFETY
-- Performing Test HAVE_CXX_FLAG_WTHREAD_SAFETY - Failed
-- Performing Test HAVE_CXX_FLAG_COVERAGE
-- Performing Test HAVE_CXX_FLAG_COVERAGE - Success
-- Compiling and running to test HAVE_STD_REGEX
-- Performing Test HAVE_STD_REGEX -- compiled but failed to run
-- Compiling and running to test HAVE_GNU_POSIX_REGEX
-- Performing Test HAVE_GNU_POSIX_REGEX -- failed to compile
-- Compiling and running to test HAVE_POSIX_REGEX
-- Performing Test HAVE_POSIX_REGEX -- compiled but failed to run
CMake Error at CMakeLists.txt:299 (message):
  Failed to determine the source files for the regular expression backend


-- Configuring incomplete, errors occurred!
benchmark/1.8.2:
benchmark/1.8.2: ERROR: Package 'e7f09c57b624b2100ef636844c070bdce803af28' build failed
benchmark/1.8.2: WARN: Build folder /home/thomas/.conan/data/benchmark/1.8.2/_/_/build/e7f09c57b624b2100ef636844c070bdce803af28/build/RelWithDebInfo
ERROR: benchmark/1.8.2: Error in build() method, line 89
        cmake.configure()
        ConanException: Error 1 while executing cmake -G "Unix Makefiles" -DCMAKE_TOOLCHAIN_FILE="/home/thomas/.conan/data/benchmark/1.8.2/_/_/build/e7f09c57b624b2100ef636844c070bdce803af28/build/RelWithDebInfo/generators/conan_toolchain.cmake" -DCMAKE_INSTALL_PREFIX="/home/thomas/.conan/data/benchmark/1.8.2/_/_/package/e7f09c57b624b2100ef636844c070bdce803af28" -DCMAKE_POLICY_DEFAULT_CMP0091="NEW" -DCMAKE_BUILD_TYPE="RelWithDebInfo" "/home/thomas/.conan/data/benchmark/1.8.2/_/_/build/e7f09c57b624b2100ef636844c070bdce803af28/src"

My current workaround is to remove the cross_building check in the recipe.
conan-io/conan-center-index@246b029
Is there a better way?
I think it would also work to update my build server to Debian12.
UPDATE: I now use a Debian12 build-container, it compiles as expected.