Unable to build Botan for Android on Windows

Question

I cannot understand how to build Botan for android, according on the instruction here:

$ export CXX=/opt/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android28-clang++

$ ./configure.py --os=android --cc=clang --cpu=arm64

i cannot understand how to use this commands on Windows, also reading previous issues did not help me, can you tell me how did you build this library on windows step-by-step, just your command examples?

I used --cc-bin option of configure.py to specify the path to the compiler, it is considered a solution for windows, but what i have is:

D:\Programming\Libraries\botanAndroid\botan-master>python configure.py --cc-bin=D:\Android\android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\bin\armv7a-linux-androideabi28-clang++ --os=android --cc=clang --cpu=armv7
INFO: configure.py invoked with options "--cc-bin=D:\Android\android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\bin\armv7a-linux-androideabi28-clang++ --os=android --cc=clang --cpu=armv7"
INFO: Configuring to build Botan 2.14.0 (revision unknown)
INFO: Running under 3.7.2 (tags/v3.7.2:9a3ffc0492, Dec 23 2018, 22:20:52) [MSC v.1916 32 bit (Intel)]
INFO: Autodetected platform information: OS="Windows" machine="AMD64" proc="Intel64 Family 6 Model 142 Stepping 10, GenuineIntel"
INFO: Canonicalized CPU target armv7 to arm32
WARNING: Could not execute ['D:\Android\android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\bin\armv7a-linux-androideabi28-clang++', '-E', 'src\build-data\detect_version.cpp']: [WinError 193] %1 is not an application of Win32
WARNING: Tried to get clang version, but output '0.0' does not match expected version format
WARNING: Could not execute ['D:\Android\android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\bin\armv7a-linux-androideabi28-clang++', '-E', '-fstack-protector', '-pthread', 'src\build-data\detect_arch.cpp']: [WinError 193] %1 is not an application of Win32
WARNING: Unable to detect target architecture via compiler macro checks
INFO: Target is clang:0.0-android-arm32
INFO: Assuming target arm32 is little endian
INFO: Skipping (dependency failure): asio certstor_sqlite3 rdrand sessions_sqlite3
INFO: Skipping (incompatible CPU): aes_armv8 aes_ni aes_power8 chacha_avx2 clmul_cpu clmul_ssse3 idea_sse2 p9_darn rdrand_rng rdseed serpent_avx2 sha1_armv8 sha1_sse2 sha1_x86 sha2_32_armv8 sha2_32_bmi2 sha2_32_x86 sha2_64_bmi2 sha3_bmi2 shacal2_avx2 shacal2_x86 simd_avx2 sm4_armv8 threefish_512_avx2
INFO: Skipping (incompatible OS): certstor_system_macos certstor_system_windows commoncrypto getentropy proc_walk win32_stats
INFO: Skipping (no enabled compression schemes): compression
INFO: Skipping (requires external dependency): boost bzip2 lzma openssl sqlite3 tpm zlib
INFO: Loading modules: adler32 aead aes aes_vperm aont argon2 aria asn1 auto_rng base base32 base58 base64 bcrypt bcrypt_pbkdf bigint blake2 block blowfish camellia cascade cast128 cast256 cbc cbc_mac ccm cecpq1 certstor_flatfile certstor_sql certstor_system cfb chacha chacha20poly1305 chacha_rng chacha_simd32 checksum cmac comb4p cpuid crc24 crc32 cryptobox ctr curve25519 des dev_random dh dl_algo dl_group dlies dsa dyn_load eax ec_group ecc_key ecdh ecdsa ecgdsa ecies eckcdsa ed25519 elgamal eme_oaep eme_pkcs1 eme_raw emsa1 emsa_pkcs1 emsa_pssr emsa_raw emsa_x931 entropy fd_unix ffi filters fpe_fe1 gcm gmac gost_28147 gost_3410 gost_3411 hash hash_id hex hkdf hmac hmac_drbg hotp http_util idea iso9796 kasumi kdf kdf1 kdf1_iso18033 kdf2 keccak keypair lion locking_allocator mac mce mceies md4 md5 mdx_hash mem_pool mgf1 misty1 mode_pad modes mp newhope nist_keywrap noekeon noekeon_simd numbertheory ocb ofb par_hash passhash9 pbes2 pbkdf pbkdf1 pbkdf2 pem pgp_s2k pk_pad pkcs11 poly1305 poly_dbl prf_tls prf_x942 psk_db pubkey rc4 rfc3394 rfc6979 rmd160 rng roughtime rsa salsa20 scrypt seed serpent serpent_simd sessions_sql sha1 sha2_32 sha2_64 sha3 shacal2 shacal2_simd shake shake_cipher simd siphash siv skein sm2 sm3 sm4 socket sodium sp800_108 sp800_56a sp800_56c srp6 stateful_rng stream streebog system_rng thread_utils threefish_512 tiger tls tls_10 tls_cbc tss twofish utils uuid whirlpool x509 x919_mac xmss xtea xts
INFO: Using hardlink to link files into build dir (use --link-method to change)
INFO: Botan 2.14.0 (revision unknown) (unreleased undated) build setup is complete

Now i'm currently using VisualStudio 2017 native tool command prompt, or calling vcvarsall.bat, to set up the environment.

Answer 1

It seems Botan support for building Android binaries on Windows hosts is limited. You will have to use dark magic to make this work.

The build process consists of two phases, the configuration phase and the make phase.

The Android-specific instructions in the documentation you linked do not cover the whole build process, only the configuration phase. For the make phase, you then have to follow the Windows-specific instructions (link).

Configuration phase:

You will need the following binaries, adjust the paths to your machine:

• clang++ (note the .cmd at the end): C:\Development\android-ndk-r19c-windows-x86_64\android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\bin\armv7a-linux-androideabi28-clang++.cmd

• ar: C:\Development\android-ndk-r19c-windows-x86_64\android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\bin\arm-linux-androideabi-ar.exe

In the Botan folder, run the configure command:

python.exe .\configure.py --cc-bin=C:\Development\android-ndk-r19c-windows-x86_64\android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\bin\armv7a-linux-androideabi28-clang++.cmd --ar-command=C:\Development\android-ndk-r19c-windows-x86_64\android-ndk-r19c\toolchains\llvm\prebuilt\windows-x86_64\bin\arm-linux-androideabi-ar.exe --os=android --cpu=armv7 --verbose

Make phase

The configuration phase generates a Makefile in the Botan folder. You will have to make some adjustments to this file:

• In the line all: libs cli tests docs remove docs

  Reason: Additional tools are needed for building the documentation files. If you really need the documentation, you could also try to install these tools, but I have not tested this.

• Replace the occurrences of ln -fs with copy.

  Reason: On Linux ln -fs would create a symbolic link from the second file in the parameter list to the first. This command is not available, so changing it to copying the first file to the second seems like a pragmatic work-around to me. You could also change it to the appropriate command for creating a link on Windows, but then you might have to adjust it again when deploying to your Android target.

• In the lines starting with LIBOBJS =, CLIOBJS = and TESTOBJS =, replace all occurrences of \ with /. In the whole file, replace occurrences of .\ with ./. Reason: Using the Windows-style path separator \ seems to cause problems in some places.

• Find the block with # Executable targets and # Library targets. Insert @<< ... << around the parameter lists (known as the nmake inline file feature, based on this answer), to make it look like this:

# Executable targets
$(CLI): $(LIBRARIES) $(CLIOBJS)
  $(EXE_LINK_CMD) @<<
$(ABI_FLAGS) $(CLIOBJS) $(EXE_LINKS_TO) $(LDFLAGS) -o $@
<<

$(TEST): $(LIBRARIES) $(TESTOBJS)
  $(EXE_LINK_CMD) @<<
$(ABI_FLAGS) $(TESTOBJS) $(EXE_LINKS_TO) $(LDFLAGS) -o $@
<<

# Library targets
./libbotan-2.a: $(LIBOBJS)
  $(AR) @<<
$(AR_OPTIONS) $@ $(LIBOBJS)
<<

./libbotan-2.so.13: $(LIBOBJS)
  $(CXX) @<<
-shared -fPIC -Wl,-soname,libbotan-2.so.13  $(ABI_FLAGS) $(LDFLAGS) $(LIBOBJS) $(LIB_LINKS_TO) -o $@
<<

Reason: Without this change, I got an error about the parameter list being too long.

You will need nmake (part of Visual Studio). On my machine it is installed in C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.25.28610\bin\Hostx64\x64\nmake.exe

In the Botan folder, run nmake.exe. Afterwards, your Botan folder should contain the binaries botan, botan-test and libraries libbotan-2....