Clang++ /usr/bin/ld: unrecognised emulation mode: armelf_linux_eabi

I am developing a cross platform C++ project for Android with armv7-a architecture on Linux 64 bit as host machine. I use Android NDK r25c and stopped to build the final executable file by this output from my makefile:

clang++ --target=armv7a-linux-androideabi33 --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c Packet.cpp -o     ../bin/Packet.o     -std=c++17 
clang++ --target=armv7a-linux-androideabi33 --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c Client.cpp -o     ../bin/Client.o     -std=c++17
clang++ --target=armv7a-linux-androideabi33 --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c Server.cpp -o     ../bin/Server.o     -std=c++17
clang++ --target=armv7a-linux-androideabi33 --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c Shell.cpp -o      ../bin/Shell.o      -std=c++17
clang++ --target=armv7a-linux-androideabi33 --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c Filesystem.cpp -o ../bin/Filesystem.o -std=c++17
clang++ --target=armv7a-linux-androideabi33 --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c client_main.cpp -o ../bin/client_main.o -std=c++17
clang++ --target=armv7a-linux-androideabi33 --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c server_main.cpp -o ../bin/server_main.o -std=c++17
clang++ --target=armv7a-linux-androideabi33 --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -o ../bin/cmain.out ../bin/Filesystem.o ../bin/Shell.o ../bin/Packet.o ../bin/Client.o ../bin/client_main.o
/usr/bin/ld: unrecognised emulation mode: armelf_linux_eabi
Supported emulations: elf_x86_64 elf32_x86_64 elf_i386 elf_iamcu i386pep i386pe elf64bpf
clang-15: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [makefile:39: android] Error 1

All *.o files have been constructed and running file command on them gives:

> ELF 32-bit LSB relocatable, ARM, EABI5 version 1 (SYSV), not stripped

But the very last command to link all *.o files together and create the executable file fails.

Does anybody have any idea?

This is after my own solution (in case anyone is interested):

The installation of Android NDK was just downloading and extraction of the zip file. To set up the cross compiling toolchains, I would refer to the Solution that I made after a lot of trial and error because actually I could not find any assistance anywhere. The build environment was nothing but liunx terminal (no Android studio nor Gradle).

And this is my makefile:

export NDK_DIR     = /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64
export ANDROID_CXX = $(NDK_DIR)/bin/clang++
export TARGET      = --target=armv7a-linux-androideabi31 
export SYSROOT     = --sysroot=$(NDK_DIR)/sysroot
export CPP_VERSION = -std=c++17                          

android:
# compile single *.cpp files into separate *.o files
    $(ANDROID_CXX) $(TARGET) $(SYSROOT) -Iinclude -c Packet.cpp -o     ../bin/Packet.o     $(CPP_VERSION)
    $(ANDROID_CXX) $(TARGET) $(SYSROOT) -Iinclude -c Client.cpp -o     ../bin/Client.o     $(CPP_VERSION)
    $(ANDROID_CXX) $(TARGET) $(SYSROOT) -Iinclude -c Server.cpp -o     ../bin/Server.o     $(CPP_VERSION)
    $(ANDROID_CXX) $(TARGET) $(SYSROOT) -Iinclude -c Shell.cpp -o      ../bin/Shell.o      $(CPP_VERSION)
    $(ANDROID_CXX) $(TARGET) $(SYSROOT) -Iinclude -c Filesystem.cpp -o ../bin/Filesystem.o $(CPP_VERSION)

# compile two entry points for server and client and convert their *.cpp files into separate *.o files
    $(ANDROID_CXX) $(TARGET) $(SYSROOT) -Iinclude -c client_main.cpp -o ../bin/client_main.o $(CPP_VERSION)
    $(ANDROID_CXX) $(TARGET) $(SYSROOT) -Iinclude -c server_main.cpp -o ../bin/server_main.o $(CPP_VERSION)

# compile and link all object files into two separate *.out files (one for client and one for server)
    $(ANDROID_CXX) $(TARGET) $(SYSROOT) -o ../bin/cmain.out ../bin/Filesystem.o ../bin/Shell.o ../bin/Packet.o ../bin/Client.o ../bin/client_main.o
    $(ANDROID_CXX) $(TARGET) $(SYSROOT) -o ../bin/server_executable.out ../bin/Filesystem.o ../bin/Shell.o ../bin/Packet.o ../bin/Server.o ../bin/server_main.o

# remove single *.o files
    rm -f ../bin/Android/Packet.o    
    rm -f ../bin/Android/Client.o    
    rm -f ../bin/Android/Server.o    
    rm -f ../bin/Android/Shell.o     
    rm -f ../bin/Android/Filesystem.o
    rm -f ../bin/Android/client_main.o
    rm -f ../bin/Android/server_main.o

Answer:

The whole pain now is gone by simply making a symbolic link of clang-14 inside /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin directory.

Perhaps, if in future, someone else will face the same problem as me, here is the solution:

1. go to your toolchain's binary directory (e.g. mine is /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin)

2. there should be a text file called clang++. it is just a wrapper file pointing to clang-14 compiler binary fie which resides in the same path, if you look for it.

3. rename this text file to something else just for not losing it later (I did mv ./clang++ ./clang++1)

4. Now make a symbolic link for your compiler by ln -s ./clang-14 ./clang++.

5. now you can call this symbolic link from your makefile and this is the output:

   /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7a-linux-androideabi33  --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c Packet.cpp -o     ../bin/Packet.o     -std=c++17
   /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7a-linux-androideabi33  --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c Client.cpp -o     ../bin/Client.o     -std=c++17
   /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7a-linux-androideabi33  --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c Server.cpp -o     ../bin/Server.o     -std=c++17
   /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7a-linux-androideabi33  --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c Shell.cpp -o      ../bin/Shell.o      -std=c++17
   /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7a-linux-androideabi33  --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c Filesystem.cpp -o ../bin/Filesystem.o -std=c++17
   /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7a-linux-androideabi33  --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c client_main.cpp -o ../bin/client_main.o -std=c++17
   /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7a-linux-androideabi33  --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -Iinclude -c server_main.cpp -o ../bin/server_main.o -std=c++17
   /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7a-linux-androideabi33  --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -o ../bin/cmain.out ../bin/Filesystem.o ../bin/Shell.o ../bin/Packet.o ../bin/Client.o ../bin/client_main.o
   /usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7a-linux-androideabi33  --sysroot=/usr/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/sysroot -o ../bin/server_executable.out ../bin/Filesystem.o ../bin/Shell.o ../bin/Packet.o ../bin/Server.o ../bin/server_main.o