Develop Reference

Linux supports splice() and sendfile(), how about Android?

Does Android support splice() and sendfile()?

These are Linux kernel calls, so they do exist on Android.
The more interesting question is if Bionic libc provides wrappers as it does for most ordinarily used system calls, or if you will have to invoke them directly. Additionally, apart from being included in Bionic there is the question of the functionality being exported for general use in the NDK.
It appears that sendfile() has been there since the first NDK release.
splice() has not historically seemed to be part of the NDK (I did not check the latest), though it was added to the AOSP sources of Bionic libc in June 2014.
Incidentally grep -r on relevant parts of the NDK installation and/or an AOSP Bionic checkout is a quick way to look into things like this.

Ndk doesn't support splice(). When I was trying to compile dirtypipe exploit for android.

cmake vs waf: mainly for c++ windows/linux and android

After searching a lot and reading a lot of information, I cannot decide which tool I should use for compiling my code. My codebase is mainly c++. I use primarily linux as my development machine.
Based on opinions I read before, my final candidates are waf and cmake, but I cannot decide myself which one should be more appropiate.
My primary requirements are:
Must be able to compile software in windows/linux and android.
Must be ready to run tests.
Must be able to play nicely with other libraries that must be compiled with another build system but most likely will have to be compiled from source.
Must be able to add custom steps, like for example, generating some data from some files (mainly graphics) before compiling, all integrated in the build system.
Some strong preferences are:
Being ready to support MAC compilation.
Being able to cross-compile from linux as many platforms as I can (maybe windows/linux/android but cannot MAC?)
Being able to add support for iOS compilation if the need arises.
Would be nice if the invocation interface was similar to that of autotools, since it is the one many people know and it is well documented.
Some questions:
If I have some rare requirement, which build system would be more ready to be extended?
Are both currently well maintained? (I wonder about waf mainly).
Community: if I find a problem, both communities are big enough to support me, in your experience?
For now my feeling is that I favour waf a bit as a tool, but cmake seems to have been quite successful for whatever reason.

Don't know much about waf, but CMake fits your requirements pretty well. I do know waf is written in Python, my personal favourite programming language ATM.
My primary requirements are:
Must be able to compile software in windows/linux and android.
CMake does Windows and Linux very well but so does any other build system worth its salt.
Someone wrote some Android scripts for CMake. Can't find anything similar for waf (my Google-fu turns up nothing.)
Must be ready to run tests.
CMake has a sibling testing framework.
Must be able to play nicely with other libraries that must be compiled with another build system but most likely will have to be compiled from source.
CMake has good integration with pkg-config, and can link against arbitrary shared libraries.
Must be able to add custom steps, like for example, generating some data from some files (mainly graphics) before compiling, all integrated in the build system.
CMake can generate custom rules.
Some strong preferences are:
Being ready to support MAC compilation.
CMake supports Mac quite well. It will even make you an Xcode project if you want, but it can also do command line builds.
Being able to cross-compile from linux as many platforms as I can (maybe windows/linux/android but cannot MAC?)
Cross-compiling is supported in CMake. CMake will not be the primary source of pain with cross-compiling - literally everything else will.
Especially with regards to cross-compiling for Mac. It's possible, but not worth it to cross-compile for that platform, considering you need access to a Mac anyways to get the libraries and header files, you need to patch GCC and clang and LLVM, etc. The only sound reason I've heard for going through this much pain is running an automated build server. Anyways, if you get a working Linux -> Mac toolchain, you should be able to cross-compile with CMake as if it were any other Unix platform.
Being able to add support for iOS compilation if the need arises.
iOS cross-compilation can be done, but you need a Mac.
Would be nice if the invocation interface was similar to that of autotools, since it is the one many people know and it is well documented.
Write a configure script that just calls CMake (cmake .). Then your users can do a ./configure && make && make install on platforms where that makes sense. There's also CPack which lets you generate DEB, RPM, NSIS (Windows) and DMG (Mac) installers/packages.
Some questions:
If I have some rare requirement, which build system would be more ready to be extended?
CMake is very extensible. It can be extended to support new languages and target platforms. (Given that waf is written in Python, it's going to be pretty hackable too.)
Are both currently well maintained? (I wonder about waf mainly).
CMake is mature and well-maintained.
Community: if I find a problem, both communities are big enough to support me, in your experience?
The community and extensions available are what keeps me coming back to CMake, from things like bakefile, honestly.

WAF
is pure Python
becomes part of your project, i.e. no external dependency
supports many build tools
can be used to do all kind of automations, not just building
It works perfectly for Linux, Mac or Windows.
On Android, gradle is the chosen build tool of Google. To use that is
wise, because it is set up to work by Google. You can call waf from
gradle and vice-versa, though.
If you want to learn all the low level Android
SDK tools, you could also use
WAF directly.
The SDK has
javac for Android Runtime (formerly Dalvik), Android\'s JVM, and produces a .class file
jar can also be used for Android
d8 (formerly dx) produces .dex files, with Dalvik executable code
aapt2 can then produce the .apk
javac and jar are known to WAF. For dx and aapt2 you would need
to create your own tasks, which is very
easy.
You would best make a WAF tool and
share it. Tools are either part of WAF or there is
waftools.
There are also these Steinwurf
tools.
If you make Android native code using
NDK:
you use CLANG, which is known to WAF
Further on you mentioned requirements:
WAF has waf_unit_test
WAF can do gnu_cross compilation. The Gnu toolchain knowns many
targets. But for Android you would need to set things up yourself
using the SDK or NDK. For NDK you could use the Gnu toolchain.
You would do waf configure, waf build instead of configure,
make, but you could wrap a Configure or Makefile around waf to
have the same commands.
WAF is very easily extendible with Python
WAF is now on gitlab and
constantly worked on.
The community is surely smaller than for CMake. But it is Python.
You can look into it and find out for yourself. You can also
contribute and become part of the community.

Profiling android-ndk plain C/C++ executable

What is the best way to profile plain C/C++ android executables on a rooted android device?
android-ndk-profiler seems to support only ndk libraries linked to Java.
Any suggestions?
Thanks

I was faced with the same question recently. After looking into several alternatives I decided the best option (the one I made to work, at any rate) was to build Valgrind for Android.
This page describes how to build Valgrind for Android. See also my GitHub project for a slightly different build procedure, usage notes and prebuilt Android ARMv7 binaries.

Android NDK profiler work by GCC compiler trick so should work independent
of JNI
This link has the details
http://code.google.com/p/android-ndk-profiler/wiki/HowItWorks
As long as you can insert the startup and cleanup code into your C/C++ code it should work
You can find all the information you will need here
http://code.google.com/p/android-ndk-profiler/

Android-Ndk vs Cross-Compile? Both work, but what was the need of Android NDK then?

I can cross-compile any C/C++ application, statically link it Linux libraries and run it on Android. What was the need of an Android-ndk then? Android-ndk limits us to bionic which has a small subset of gnu libc. Isn't it a better idea to straightaway cross-compile applications and run them through Android shell? Is there any limitation to cross-compiling that I can't see? This URL : Can Linux apps be run in Android? answers my question to some extent but eventually leaves me confused and without clarity.

I think this is enough for Android-NDK
The Android NDK is a companion tool to the Android SDK that lets you build performance-critical portions of your apps in native code. It provides headers and libraries that allow you to build activities, handle user input, use hardware sensors, access application resources, and more, when programming in C or C++. If you write native code, your applications are still packaged into an .apk file and they still run inside of a virtual machine on the device. The fundamental Android application model does not change.
The NDK provides:
A set of tools and build files used to generate native code libraries
from C and C++ sources
A way to embed the corresponding native libraries into an application
package file (.apk) that can be deployed on Android devices
A set of native system headers and libraries that will be supported
in all future versions of the Android platform, starting from Android
1.5. Applications that use native activities must be run on Android 2.3 or later.
This thing you can not find in other cross-compilation with arm toolchain..

As mentioned in the link http://developer.android.com/sdk/ndk/index.html NDK is a companion for App development folk to create performance sensitive native code. NDK exposes some of the native implementation of Android which could not be found in the general Linux environments. Some of them include the Android/Bitmap, Android/nativeWindow etc. Using these Android natives applcation can speed up CPU intensive processes like some compression or decompression of images.
Even though the externally cross-compiled executables may run in the Android there no guarantee that versions of the standard library implementaions are the same. NDK provides a easier and Android compatible toolchain and other resources, using which is much easier to application developers than having to find a compatible cross-compiler for their usecase.

Is it possible to compile LLVM libraries to android/ARM

I'm fascinated by the Pure algebraic/functional language. The Pure interpreter uses the LLVM JIT compiler as its backend.
I would like to compile Pure so that it runs on Android(ARM). Pure has a dependency on the LLVM JIT. So I need to compile LLVM source for Pure to run.
Is it possible to compile LLVM source for Android (ARM) devices? There really seems to be no information about this on the web. Maybe my search terms are wrong. Searching for Android LLVM does not bring up many good hits either.

It now seems possible, the NDK now supports Clang which uses LLVM. So maybe it can be made to work with any LLVM language. AOSP should give us some insight on how they added Clang support. See the latest Android NDK for details on Clang support.
Android NDK, Revision 8c (November 2012)
Important changes:
Added the Clang 3.1 compiler to the NDK. The GNU Compiler Collection (GCC) 4.6 is still the default, so you must explicitly enable the Clang compiler option as follows:
For ndk-build, export NDK_TOOLCHAIN_VERSION=clang3.1 or add this environment variable setting to Application.mk.
For standalone builds, add --llvm-version=3.1 to make-standalone-toolchain.sh and replace CC and CXX in your makefile with /bin/clang and /bin/clang++. See STANDALONE-TOOLCHAIN.html for details.
Note: This feature is experimental. Please try it and report any issues.

While you can surely compile LLVM on ARM (it's pretty trivial - just ordinary configure + make system), you're still out of luck: JIT on ARM is still work-in-progress, so I'd not expect it working for everything non-trivial.

It seems like the Android NDK would help in this, as one of its usages per its FAQ page is to reuse C/C++ code.

I think we shuld see on mix of LLVM + Android NDK (C++).
I'm thinking about SmallTalk-like dymanic object system (*), and LLVM usage is very interesting for lazy dynamic compilation on Android devices.
First try you shuld build something like tiny Buildroot/OpenWrt Linux system (or build you own using CLFS or my scripts: https://github.com/ponyatov/L/tree/clock )
for ARM device like Raspberry Pi (it's my case for testing). If you got good results on this variant, later you can migrate to Android device itself. I think you'll need some C++/NDK glue code to adopt LLVM/Pure core vs Android runtime and GUI. (**)
(*) but with my own language syntax, lisp-like functional abilities to mutate all system internals, parser/compiler integrated framework, and maybe some basics of symbolic computer algebra
(**) is Android Pi alive ?

As far as I know you can't build LLVM for ARM devices just yet.