Android System Image Issues
===========================

This document contains a list of known issues in existing Android
system images that NDK developers should be aware of.

I. Android 1.5 System Issues:
-----------------------------

The following issues correspond to the official Android 1.5
system images:


No standard C++ library support:
--------------------------------

The Android 1.5 system does not use any C++ standard library, and does
not provide one to applicative native code. Instead, a very limited set
of headers are provided (see docs/STABLE-APIS.TXT) which correspond to
the C++ support code used to build the Android platform.

It is possible to hack existing C++ STL implementations to work on top
of this, but this is not supported yet. We recommend trying with uSTL
and STLport at this point if you really need this.


No support for C++ exceptions and RTTI:
---------------------------------------

The Android 1.5 system image lacks several features necessary to reliably
implement C++ exceptions and RTTI. C++ code that depends on these features
will simply not link or run appropriately on Android 1.5


C Library limitations:
----------------------

The C library doesn't try to implement every feature under the sun.
Most notably, pthread cancellation is not supported. A detailed overview
of the C library and its design is available in docs/system/libc/OVERVIEW.TXT


No SysV IPCs in C library:
--------------------------

Unix System V Inter-Process Communication APIs (e.g. semget()) are
intentionally not available from the C library, to avoid denial-of-service
issues. See docs/system/libc/SYSV-IPC.TXT for details.


C Library bug: getservbyname() returns port number in incorrect order:
----------------------------------------------------------------------

The Android 1.5 C library function getservbyname() returns the port number
corresponding to a given network service in incorrect order. The function
stores its result in a 'struct servent' structure, and the port number in
its 's_port' field.

The standard mandates that this value is stored in network order (and thus
should be converted to host order through ntohs()). However, the 1.5
implementation is buggy and returns the number.

This bug is fixed in later releases of the platform, and applications
should not depend on the wrong behaviour in the future. Avoid using this
function if possible; if this is not possible, try to use a small wrapper
like the following one:

static struct servent*
my_getservbyname(const char*  name, const char*  proto)
{
    static int       has_bug = -1;
    struct servent*  ret;

    if (has_bug < 0) {
        ret = getservbyname("http",NULL);
        has_bug = (ret == NULL || ret->s_port == 80);
    }

    ret = getservbyname(name, proto);
    if (has_bug)
        ret->s_port = htons(ret->s_port);
}

(the returned struct servent is thread-local and can be modified by the
 caller. It will be over-written on the next call to the function though).


Dynamic Linker limitations:
---------------------------

The Android dynamic linker in 1.5 has many important limitations:

- No support for LD_LIBRARY_PATH, LD_PRELOAD, RTLD_LOCAL and many
  other options.

- Static C++ constructors in executables are called twice due to a bug
  in the C library initialization sequence. However, static C++
  constructors in shared libraries are only called once.

- Static destructors are never called at the moment, either at program
  exit, or when dlclose() is called.

- dlerror() reporting is very limited and only provides a few generic
  error messages that make it difficult to know why a dynamic load/link
  operation failed. Most of the time, the culprit is a missing symbol.

- A bug prevents one application shared library from depending on another
  one. For example, if you build both libfoo.so and libbar.so for your
  application, and list libfoo.so as a dependency for libbar.so in
  bar/Android.mk (with LOCAL_SHARED_LIBRARIES := foo), then loading
  libbar.so will always fail, even if you have already loaded libfoo.so
  in your process.

