1 <html><body><pre>Android System Image Issues 2 =========================== 3 4 This document contains a list of known issues in existing Android 5 system images that NDK developers should be aware of. 6 7 I. Android 1.5 System Issues: 8 ----------------------------- 9 10 The following issues correspond to the official Android 1.5 11 system images: 12 13 14 C++ Runtime Support: 15 -------------------- 16 17 The Android C++ system runtime only provides very little support for 18 C++ features (i.e. RTTI, exceptions and Standard Library). However, 19 the NDK provides more advanced runtimes that can be linked into your 20 application, if you need them. 21 22 See docs/CPLUSPLUS-SUPPORT.html for more details. 23 24 25 C Library limitations: 26 ---------------------- 27 28 The C library doesn't try to implement every feature under the sun. 29 Most notably, pthread cancellation is not supported. A detailed overview 30 of the C library and its design is available in docs/system/libc/OVERVIEW.html 31 32 33 No SysV IPCs in C library: 34 -------------------------- 35 36 Unix System V Inter-Process Communication APIs (e.g. semget()) are 37 intentionally not available from the C library, to avoid denial-of-service 38 issues. See docs/system/libc/SYSV-IPC.html for details. 39 40 41 C Library bug: getservbyname() returns port number in incorrect order: 42 ---------------------------------------------------------------------- 43 44 The Android 1.5 C library function getservbyname() returns the port number 45 corresponding to a given network service in incorrect order. The function 46 stores its result in a 'struct servent' structure, and the port number in 47 its 's_port' field. 48 49 The standard mandates that this value is stored in network order (and thus 50 should be converted to host order through ntohs()). However, the 1.5 51 implementation is buggy and returns the number. 52 53 This bug is fixed in later releases of the platform, and applications 54 should not depend on the wrong behaviour in the future. Avoid using this 55 function if possible; if this is not possible, try to use a small wrapper 56 like the following one: 57 58 static struct servent* 59 my_getservbyname(const char* name, const char* proto) 60 { 61 static int has_bug = -1; 62 struct servent* ret; 63 64 if (has_bug < 0) { 65 ret = getservbyname("http",NULL); 66 has_bug = (ret == NULL || ret->s_port == 80); 67 } 68 69 ret = getservbyname(name, proto); 70 if (has_bug) 71 ret->s_port = htons(ret->s_port); 72 } 73 74 (the returned struct servent is thread-local and can be modified by the 75 caller. It will be over-written on the next call to the function though). 76 77 78 Dynamic Linker limitations: 79 --------------------------- 80 81 The Android dynamic linker in 1.5 has many important limitations: 82 83 - No support for LD_LIBRARY_PATH, LD_PRELOAD, RTLD_LOCAL and many 84 other options. 85 86 - Static C++ constructors in executables are called twice due to a bug 87 in the C library initialization sequence. However, static C++ 88 constructors in shared libraries are only called once. 89 90 - Static destructors are never called at the moment, either at program 91 exit, or when dlclose() is called. 92 93 - dlerror() reporting is very limited and only provides a few generic 94 error messages that make it difficult to know why a dynamic load/link 95 operation failed. Most of the time, the culprit is a missing symbol. 96 97 - A bug prevents one application shared library from depending on another 98 one. For example, if you build both libfoo.so and libbar.so for your 99 application, and list libfoo.so as a dependency for libbar.so in 100 bar/Android.mk (with LOCAL_SHARED_LIBRARIES := foo), then loading 101 libbar.so will always fail, even if you have already loaded libfoo.so 102 in your process. 103 104 </pre></body></html> 105
