Re: Building for Android

[Aris Adamantiadis <aris@xxxxxxxxxxxx>]

Hi Matteo,

This is really strange. All _ssh_log is doing is preparing a buffer,
it's not even the function that's writing on stderr. Does it still
happen if you set the verbosity to -1 (absolutely silent) ?

Can you reproduce the issue in the android emulator? if so, could you
share the APK ?

Thanks,

Aris

On 21/11/15 03:24, Matteo wrote:
> Hi Aris,
>
> Thank you for your interest, and for a great library.
>
> I have good news: it seems to work now.
> And the funny thing is, it seems to have something to do with logging.
>
> Quick recap here, but feel free to ask for more informations:
> The problem is that, unfortunately, my device is not rooted, and thus
> access to logs and stacktraces is limited.
> So, while trying to find an efficient way to log library events, I
> stumbled upon the ssh_set_log_callback() function.
> That seemed perfect in this case, as I can redirect the log messages to
> screen and to a "private" log file that the app has access to.
>
> So I quickly implemented it into the tester program and... to my
> surprise, no crash anymore!
> I could successfully establish a connection, as confirmed also by the
> server logs.
>
> Here the working code:
> void callback(int priority, const char *function, const char *buffer,
> void *userdata)
> {
>     //this function can be empty, does not make any difference
> }
>
> 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);
>
>     //added these lines for logging
>     session.setOption(SSH_OPTIONS_LOG_VERBOSITY, 2);
>     ssh_set_log_level(SSH_LOG_FUNCTIONS);
>     ssh_set_log_callback(callback); //commenting out this line causes
> the crash
>
>     session.connect();
> }
>
> My guess is that libSSH is logging to some facility that, on Android,
> the app does not have access to.
> Please find attached an excerpt from the Android logcat with a stacktrace.
> The log starts with a "touch event" corresponding to pushing the button
> connected to MainWindow::test(), and ends with the app crashing.
> From the stacktrace, one can see that the last called function seems to
> be _ssh_log().
>
> Tomorrow I will try to slowly expand the test to a more complete use case.
>
> Regards
> Matteo
>
> On 11/20/2015 07:34 PM, Aris Adamantiadis wrote:
>> 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
>>>>>
>>>>>