Cannot cross-compiling code using clang++ - arm

Question

Command:
I am trying to cross compile a simple C++ program using clang++. I'm using Linaro gcc tool-chain to obtain the library and other includes required.
${root}/bin/clang++ --target=arm-linux-gnueabihf --rtlib=compiler-rt --stdlib=libc++ -nostdinc++ -I${root}/include/c++/v1 -Wl,-L${root}/lib --sysroot ${sysroot} --gcc-toolchain=/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf -rpath ${root}/lib TestCodeX86toARM.cpp -o Test -v
The value of root and sysroot is as follows:
root=/path/to/clang/install_dir
sysroot=/path/to/linarogcc/arm-linux-gnueabihf/libc
TestCodeX86toARM.cpp is just a hello world code
output:
clang version 10.0.0
Target: arm-unknown-linux-gnueabihf
Thread model: posix
InstalledDir: /home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/bin
Found candidate GCC installation: /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/lib/gcc/arm-linux-gnueabihf/7.5.0
Selected GCC installation: /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/lib/gcc/arm-linux-gnueabihf/7.5.0
Candidate multilib: .;#m32
Selected multilib: .;#m32
"/home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/bin/clang-10" -cc1 -triple armv6kz-unknown-linux-gnueabihf -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name TestCodeX86toARM.cpp -mrelocation-model static -mthread-model posix -mframe-pointer=all -fmath-errno -fno-rounding-math -masm-verbose -mconstructor-aliases -target-cpu arm1176jzf-s -target-feature +strict-align -target-abi aapcs-linux -mfloat-abi hard -fallow-half-arguments-and-returns -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v -nostdinc++ -resource-dir /home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/lib/clang/10.0.0 -I /home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/include/c++/v1 -isysroot /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc -internal-isystem /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/usr/local/include -internal-isystem /home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/lib/clang/10.0.0/include -internal-externc-isystem /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/include -internal-externc-isystem /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/usr/include -fdeprecated-macro -fdebug-compilation-dir /home/user/Tejas/CrossCopileTestCode -ferror-limit 19 -fmessage-length 0 -fno-signed-char -fgnuc-version=4.2.1 -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -faddrsig -o /tmp/TestCodeX86toARM-438a38.o -x c++ TestCodeX86toARM.cpp
clang -cc1 version 10.0.0 based upon LLVM 10.0.0 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/usr/local/include"
ignoring nonexistent directory "/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/include"
#include "..." search starts here:
#include <...> search starts here:
/home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/include/c++/v1
/home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/lib/clang/10.0.0/include
/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/usr/include
End of search list.
"/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/lib/gcc/arm-linux-gnueabihf/7.5.0/../../../../arm-linux-gnueabihf/bin/ld" --sysroot=/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc -EL -z relro -X --hash-style=gnu --eh-frame-hdr -m armelf_linux_eabi -dynamic-linker /lib/ld-linux-armhf.so.3 -o Test /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/usr/lib/../lib/crt1.o /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/usr/lib/../lib/crti.o /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/lib/gcc/arm-linux-gnueabihf/7.5.0/crtbegin.o -L/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/lib/gcc/arm-linux-gnueabihf/7.5.0 -L/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/lib/gcc/arm-linux-gnueabihf/7.5.0/../../../../arm-linux-gnueabihf/lib/../lib -L/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/lib/../lib -L/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/usr/lib/../lib -L/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/lib/gcc/arm-linux-gnueabihf/7.5.0/../../../../arm-linux-gnueabihf/lib -L/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/lib -L/home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/usr/lib -L/home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/lib -rpath /home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/lib /tmp/TestCodeX86toARM-438a38.o -lc++ -lm /home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/lib/clang/10.0.0/lib/linux/libclang_rt.builtins-armhf.a -lc /home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/lib/clang/10.0.0/lib/linux/libclang_rt.builtins-armhf.a /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/lib/gcc/arm-linux-gnueabihf/7.5.0/crtend.o /home/user/Tejas/LLVM/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/usr/lib/../lib/crtn.o
/home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/lib/libc++.so.1: file not recognized: File format not recognized
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

Your linker is trying to link against libc++. However clang cant find this library in your arm tool-chain ( probably your arm tool-chain is providing libstdc++). So the only libc++ found by the linker is /home/user/Tejas/clang+llvm-10.0.0-x86_64-linux-gnu-ubuntu-18.04/lib/libc++.so.1 which is probably an x86 library ( you can confirm that with objdump or readelf).
Try to replace --stdlib=libc++ by --stdlib=libstdc++ in your command line.