Re: Building for Android

[Aris Adamantiadis <aris@xxxxxxxxxxxx>]

Hi Matteo,

You did a great work compiling libssh for android. I have no idea what's
causing the crash, it would greatly help if you could provide us with a
stacktrace. Running libssh in verbose mode and capturing the output
would also help figuring out what works .

Aris

On 20/11/15 18:46, Matteo wrote:
> After several attempts, I could get a successful build.
> However, when I test it, it segfaults.
>
> In the following, I will try to explain what I did.
> I will try to be brief but, if there is any interest, I can provide
> more detailed instructions (or even a script that automates the whole
> process).
>
> 0) The build environment is as follows:
> - Ubuntu 15.04 64 bit with 3.19.0-33 kernel
> - cmake 3.0.2 and gcc 4.9.2 (both from repos)
> - Android NDK r9d
> - OpenSSL 1.0.2d
> - libSSH 0.7.2
> - Qt 5.4 and QtCreator 3.3.0
> - Target platform arm-linux-androideabi-4.8 API 19
> - Target device Samsung Galaxy S5 klte
>
> 1) First, we need to build the dependencies.
> zlib is already part of the NDK, so we only need to cross-compile OpenSSL.
> This is easily accomplished by following the instructions found here:
> https://wiki.openssl.org/index.php/Android
> After installation I symlinked libcrypto.so, libssl.so and the include
> files inside the NDK "usr" folder (so that they can easily be linked
> against).
>
> 2) Following Daniel Kroker's advice, I added the taka-no-me toolchain
> into the libSSH folder.
> Before I could complete the build, however, I had to solve following
> problems.
>
> 3) My version of cmake has a bug that was fixed in 3.1 an later versions.
> This prevents it to correctly detect OpenSSL 1.0.2 (it is reported to
> work with earlier versions, though).
> To fix it, I manually applied this patch:
> https://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=c5d9a8283cfac15b4a5a07f18d5eb10c1f388505
>
> 4) The cmake configuration of libSSH contains a TRY_RUN() step.
> As far as I could understand, this is supposed to run a dummy test to
> check if a certain feature works correctly.
> This is obviously not possible in cross-compilation mode: fortunately,
> the error issued by cmake contains an explanation on how to fix it.
> In the libSSH folder one needs to create a file (named e.g.
> "TryRunResults.cmake") with following content:
>         set( THREADS_PTHREAD_ARG 0
>              CACHE STRING "Result from TRY_RUN" FORCE)
>
> 5) The build still fails with error "implicit declaration of function
> 'getpwuid_r'"
> This function is supposed to return informations about the current
> user, like username and home directory.
> This has no equivalent on android, so I needed to change these two
> functions in the file "misc.c":
>    char *ssh_get_user_home_dir(void)
>    char *ssh_get_local_username(void)
> For my tests, I resigned to return hard-coded values, but more work is
> required for a general solution.
>
> 6) Now the build completes successfully. These are the command issued:
> cd /path/to/downloaded/libSSH/
> mkdir build
> cd build
>         cmake \
>             -C ../TryRunResults.cmake \
>             -DCMAKE_INSTALL_PREFIX=/opt/libssh-android \
>             -DWITH_INTERNAL_DOC=OFF \
>             -DWITH_STATIC_LIB=ON \
>             -DWITH_TESTING=OFF \
>             -DWITH_SERVER=OFF \
>             -DWITH_EXAMPLES=OFF \
>             -DCMAKE_BUILD_TYPE=Release \
>             -DCMAKE_TOOLCHAIN_FILE=../android.toolchain.cmake \
>             -DANDROID_NDK="$ANDROID_NDK_ROOT" \
>             -DANDROID_NATIVE_API_LEVEL=android-19 \
>             -DANDROID_TOOLCHAIN_NAME=arm-linux-androideabi-4.8 \
>             -DANDROID_ABI="armeabi-v7a with NEON" \
>         ..
>         cmake --build .
>
> 7) Before deployment, there are two more obstacles.
> First, the Android NDK doesnt provide OpenSSL, but the library is
> installed in Android and loaded by default (taking precedence over
> libraries packaged in the APK).
> This means that we have to rename the libcrypto.so and libssl.so to
> something else, and repeat the linking step. However, see below.
> (this problem is documented here:
> https://mta.openssl.org/pipermail/openssl-users/2015-April/001183.html)
> Second, Android does not support loading of versioned libraries
> (meaning that e.g. libssh.so is a symlink to libssh.so.4.4.0).
> This means that we have to configure OpenSSL and libSSH to produce
> non-versioned files, and relink. However, see below.
> (this problem is documented here:
> https://bugreports.qt.io/browse/QTCREATORBUG-11062)
> The link above also provided a solution (hack?) for both problems,
> which I implemented with following BASH code:
>     local subs=()
>     subs+=(-e
> 's/libcrypto.so.1.0.0/libcryptm.so\x00\x00\x00\x00\x00\x00/g')
>     subs+=(-e 's/libcrypto.so/libcryptm.so/g')
>     subs+=(-e 's/libssl.so.1.0.0/libssm.so\x00\x00\x00\x00\x00\x00/g')
>     subs+=(-e 's/libssl.so/libssm.so/g')
>     subs+=(-e 's/libssh.so.4.4.0/libssh.so\x00\x00\x00\x00\x00\x00/g')
>     subs+=(-e 's/libssh.so.4/libssh.so\x00\x00/g')
>     sed "${subs[@]}" "/opt/openssl/android-19/lib/libcrypto.so" >
> "/home/matteo/deploy/libcryptm.so"
>     sed "${subs[@]}" "/opt/openssl/android-19/lib/libssl.so" >
> "/home/matteo/deploy/libssm.so"
>     sed "${subs[@]}" "/opt/libssh-android/lib/libssh.so" >
> "/home/matteo/deploy/libssh.so"
>     chmod a+x /home/matteo/deploy/*
>
> 8) I prepared a very simple test project in Qt.
> Starting from the widget-based template for android, I added a
> function that, when clicking on a QPushButton, attempts to connect to
> a ssh server in my LAN.
> void MainWindow::test()
> {
>     ssh::Session session;
>     session.setOption(SSH_OPTIONS_TIMEOUT, 20);
>     session.setOption(SSH_OPTIONS_HOST, "192.168.0.13");
>     session.setOption(SSH_OPTIONS_USER, "root");
>     session.setOption(SSH_OPTIONS_PORT, 2222);
>
>     session.connect();
> }
>
> This works if "session.connect();" is commented out, but the program
> crashes otherwise, with error:
> F/libc    (22871): Fatal signal 11 (SIGSEGV), code 1, fault addr
> 0x10100 in tid 23039 (QtThread)
> Note that the very same code works in "desktop mode".
>
> Right now I am out of ideas on how to debug this, so if someone can
> give an hint, I would much appreciate it.
> As I said above, I can provide more details and code upon request.
>
> Thanks in advance
> Matteo
>
> On 11/19/2015 09:28 AM, Daniel Kroker wrote:
>> Hi,
>>
>> its not so easy to build libssh for android. you need the android
>> toolchain look at
>> https://github.com/taka-no-me/android-cmake/blob/master/android.toolchain.cmake
>>
>> Am 19.11.2015 um 02:35 schrieb Matteo:
>>> Hi all,
>>>
>>> My project depends on libssh and I am trying to port it to Android.
>>>
>>> After some research in the Internet, it appears that I have to
>>> cross-compile libssh by using the Android NDK.
>>> However, I could not find any good sources of information about the
>>> topic.
>>>
>>> Could somebody please provide a starting point for me?
>>>
>>> Thank you in advance.
>>> Mat
>>>
>>>
>>
>