[CMake] RPATH cross-compile issue with CHECK_*_EXISTS

Mon Feb 6 20:46:39 EST 2017

I have a PR that asks the linker (via the compiler) what its implicit
search directories are instead.

It is the right way to do it IMHO, but I need to find time to finish it
unfortunately.

On Feb 6, 2017 11:16 PM, "Jörg Krause" <joerg.krause at embedded.rocks> wrote:

> On Mon, 2017-02-06 at 22:22 +0100, Jörg Krause wrote:
> > Hi,
> >
> > On Sun, 2017-02-05 at 23:03 +0100, Jörg Krause wrote:
> > > Hi,
> > >
> > > when using CHECK_{SYMBOL,FUNCTION}_EXISTS in a cross-compilation
> > > environment, CMake passes the host rpath to the linker:
> > >
> > > """ CMakeOutput.log
> > >
> > > /home/joerg/host/usr/bin/i586-linux-gcc
> > > --sysroot=/home/joerg/host/usr/i586-buildroot-linux-musl/sysroot
> > > -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64
> > > -Os   -
> > > DNDEBUG    CMakeFiles/cmTC_cb8f6.dir/CheckSymbolExists.c.o  -o
> > > cmTC_cb8f6 -Wl,-rpath,/usr/lib32 -rdynamic
> > > /home/joerg/host/usr/i586-
> > > buildroot-linux-musl/sysroot/usr/lib32/libmbedtls.so
> > > /home/joerg/host/usr/i586-buildroot-linux-
> > > musl/sysroot/usr/lib32/libmbedx509.so /home/joerg/host/usr/i586-
> > > buildroot-linux-musl/sysroot/usr/lib32/libmbedcrypto.so
> > >
> > > """
> > >
> > > This leads to a linker error if mbedtls is linked with zlib, as the
> > > linker tries to link with the host zlib and does not find the host
> > > libc:
> > >
> > > """ CMakeError.txt
> > >
> > > /home/joerg/host/usr/i586-buildroot-linux-musl/bin/ld: warning:
> > > libc.so.6, needed by /usr/lib32/libz.so.1, not found (try using
> > > -rpath
> > > or -rpath-link)
> > > /usr/lib32/libz.so.1: undefined reference to `strcpy at GLIBC_2.0'
> > > /usr/lib32/libz.so.1: undefined reference to `free at GLIBC_2.0'
> > > /usr/lib32/libz.so.1: undefined reference to `fseeko64 at GLIBC_2.1
> > > [..]
> > >
> > > """
> > >
> > > I did not find any solution which allows me to remove the rpath
> > > from
> > > the check. Setting CMAKE_SKIP_RPATH does not change the build
> > > behaviour of the check_symbol_exists macro.
> > >
> > > From my understanding, the rpath flag should not be used when the
> > > sysroot flag is passed to the linker, right?
> > >
> > > For reference, I added a minimal example which uses Buildroot for
> > > cross-compilation.
> > >
> > > """ CMakeLists.txt
> > >
> > > cmake_minimum_required(VERSION 2.8.12)
> > >
> > > project(test)
> > >
> > > list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
> > >
> > > find_package(MbedTLS)
> > > if(MBEDTLS_FOUND)
> > >     message(STATUS "Using mbedTLS")
> > > endif()
> > >
> > > """
> > >
> > > """ FindMbedTLS.cmake
> > >
> > > include(CheckSymbolExists)
> > >
> > > find_path(MBEDTLS_INCLUDE_DIRS
> > >     NAMES mbedtls/ssl.h
> > >     PATH_SUFFIXES include
> > > )
> > >
> > > find_library(MBEDTLS_LIBRARY NAMES mbedtls)
> > > find_library(MBEDX509_LIBRARY NAMES mbedx509)
> > > find_library(MBEDCRYPTO_LIBRARY NAMES mbedcrypto)
> > >
> > > if(MBEDTLS_LIBRARY AND MBEDX509_LIBRARY AND MBEDCRYPTO_LIBRARY)
> > >     set(CMAKE_REQUIRED_INCLUDES ${MBEDTLS_INCLUDE_DIRS})
> > >     set(CMAKE_REQUIRED_LIBRARIES ${MBEDTLS_LIBRARY}
> > > ${MBEDX509_LIBRARY} ${MBEDCRYPTO_LIBRARY})
> > >     check_symbol_exists(mbedtls_ssl_init "mbedtls/ssl.h"
> > > MBEDTLS_V2)
> > > endif()
> > >
> > > """
> > >
> > > """ toolchainfile.cmake
> > >
> > > string(REPLACE "/usr/share/buildroot" "" RELOCATED_HOST_DIR
> > > ${CMAKE_CURRENT_LIST_DIR})
> > >
> > > set(CMAKE_SYSTEM_NAME Linux)
> > > set(CMAKE_SYSTEM_PROCESSOR i586)
> > >
> > > set(CMAKE_C_FLAGS_DEBUG "" CACHE STRING "Debug CFLAGS")
> > > set(CMAKE_CXX_FLAGS_DEBUG "" CACHE STRING "Debug CXXFLAGS")
> > > set(CMAKE_C_FLAGS_RELEASE " -DNDEBUG" CACHE STRING "Release
> > > CFLAGS")
> > > set(CMAKE_CXX_FLAGS_RELEASE " -DNDEBUG" CACHE STRING "Release
> > > CXXFLAGS")
> > >
> > > # Build type from the Buildroot configuration
> > > set(CMAKE_BUILD_TYPE Release CACHE STRING "Buildroot build
> > > configuration")
> > >
> > > # Buildroot defaults flags.
> > > set(CMAKE_C_FLAGS "-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE
> > > -D_FILE_OFFSET_BITS=64 -Os" CACHE STRING "Buildroot CFLAGS")
> > > set(CMAKE_CXX_FLAGS "-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE
> > > -D_FILE_OFFSET_BITS=64 -Os" CACHE STRING "Buildroot CXXFLAGS")
> > > set(CMAKE_EXE_LINKER_FLAGS "" CACHE STRING "Buildroot LDFLAGS for
> > > executables")
> > >
> > > set(CMAKE_INSTALL_SO_NO_EXE 0)
> > >
> > > set(CMAKE_PROGRAM_PATH "${RELOCATED_HOST_DIR}/usr/bin")
> > > set(CMAKE_SYSROOT "${RELOCATED_HOST_DIR}/usr/i586-buildroot-linux-
> > > musl/sysroot")
> > > set(CMAKE_FIND_ROOT_PATH "${RELOCATED_HOST_DIR}/usr/i586-buildroot-
> > > linux-musl/sysroot")
> > > set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
> > > set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
> > > set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
> > > set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
> > > set(ENV{PKG_CONFIG_SYSROOT_DIR} "${RELOCATED_HOST_DIR}/usr/i586-
> > > buildroot-linux-musl/sysroot")
> > >
> > > # This toolchain file can be used both inside and outside
> > > Buildroot.
> > > set(CMAKE_C_COMPILER "${RELOCATED_HOST_DIR}/usr/bin/i586-linux-
> > > gcc")
> > > set(CMAKE_CXX_COMPILER "${RELOCATED_HOST_DIR}/usr/bin/i586-linux-
> > > g++")
> > >
> > > """
> > >
> > > What do I miss?
> >
> > Note, that this project was build using CMake 3.7.2 on Debian. When
> > using CMake 3.6.3, CMake does correctly not add rpath to the cross-
> > linker and the check_symbol_exists() succeeds.
>
> I did a git bisect. The behaviour was introduced in commit
> 896ad251de49f167f4ce3cbbcf9a6cce85a16681 [1].
>
> My suggestion is to set FIND_LIBRARY_USE_LIB32_PATHS and
> FIND_LIBRARY_USE_LIB64_PATHS to FALSE when cross-compiling on Linux.
>
> [1] https://gitlab.kitware.com/cmake/cmake/commit/896ad251de49f167f4ce3
> cbbcf9a6cce85a16681
>
> Best regards,
> Jörg Krause
> --
>
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