Re: Building for Android

[Matteo <matpen@xxxxxxx>]

Hi Aris,

Yes, I get the very same behavior in the Android emulator (ARMv7, didn't
try x86 yet).

App crashes if ssh_set_log_callback() is commented out, but works otherwise.
This does not change if verbosity is set to -1 (or to 0).

Please find the apk under the link below, let me know if you want the
source code, too.
https://app.box.com/s/q9aivh4etopcbhjbabqs6d53t2qyazwm
Matteo


On 11/21/2015 10:24 AM, Aris Adamantiadis wrote:
> 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
>>>>>>
>>>>>>
>
>

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