Develop Reference

'sizeof(off_t) != 8' when compiling libfuse for android

I'm trying to compile libfuse with NDK, my environment:
Win10(64bit) + NDK(r14b,64bit) + libfuse(3.1.0)
Error occurs in fuse_common.h, it checks size of off_t:
$ ndk-build
[armeabi-v7a] Compile thumb : fuse <= buffer.c
In file included from jni/../../libfuse/lib/buffer.c:15:
In file included from jni/../../libfuse/lib/fuse_i.h:9:
In file included from jni/../../libfuse/include\fuse.h:19:
jni/../../libfuse/include/fuse_common.h:745:13: error: bit-field
'_fuse_off_t_must_be_64bit' has negative width (-1)
{ unsigned _fuse_off_t_must_be_64bit:((sizeof(off_t) == 8) ? 1 : -1); };
^
1 error generated.
make: *** [obj/local/armeabi-v7a/objs/fuse/__/__/libfuse/lib/buffer.o] Error 1
here's the check in fuse_common.h:
struct _fuse_off_t_must_be_64bit_dummy_struct \
{ unsigned _fuse_off_t_must_be_64bit:((sizeof(off_t) == 8) ? 1 : -1); };
I searched on google, there's _FILE_OFFSET_BITS=64 definition, which can be used to change the size of off_t, I have this defined my 'Android.mk' file:
LOCAL_CFLAGS := \
....
-D_FILE_OFFSET_BITS=64 \
....
And even add this line at the beginning of fuse_common.h
#define _FILE_OFFSET_BITS 64
Still not working, how to fix it?

Update to NDK r15c. _FILE_OFFSET_BITS=64 works from there on out.
Note that most off64_t system calls weren't available until android-21. If your minSdkVersion is set below that and you use _FILE_OFFSET_BITS=64, many functions will not be available.

NOTE Provided solution is much like workaround, see #Dan's answer for reliable and official way to get 64-bit off_t.
On Android off_t is always 32-bit length, and there is no preprocessor macro that controls its size. (Though it is true only for NDK development since modern bionic allow to configure off_t size at compile time). And because of this you cannot compile your library directly.
But I guess there is some way to workaround it. Android NDK offers non-POSIX extended type - off64_t, and also it provides a complementary set of library functions that accept it instead of off_t. They are distinguished by 64 suffix, i.e. lseek64(), mmap64(). So to make things work you may try to add global configuration header to your project:
/* let off_t to be a 64-bit length */
typedef off64_t off_t;
/* use appropriate versions of system functions */
/* list here only functions that have off_t parameters and are used by your library */
#define mmap mmap64
#define lseek lseek64
And of course keep in mind that compiled code now is linked against *64() functions instead of regular ones and any public interfaces expect off64_t instead of off_t.

Android NDK seekg broken?

I am using the following code:
fileIn.seekg(12,std::ios::beg);
uint16_t data;
fileIn>>data;
LOG_D("app","file data=%u",data);
But what actually happens is it logs the value of offset I pass in seekg like in the given case it Logs
file data=12
If i use
fileIn.seekg(8,std::ios::beg);
then it prints "file data=8"
in general it prints
file data=x for fileIn.seekg(x,std::ios::beg);
its very mysterious to me ! I am using android ndk r10d c++ with eclipse for ARM thumb target

Have you checked that anything was actually read from the stream? I'm guessing you're just printing out garbage data.

How to use CallStack (in CallStack.tpp) in a executable on android platform?

A question from https://stackoverflow.com/a/11467040/1442443
my final target is to dump user space stack.
I try to build a cpp file as below to a executable on android platform. Therefore, by calling tryToGetStack(), I can get call stack of my executable in run time.
#include <utils/CallStack.h>
namespace android
{
extern "C" void tryToGetStack()
{
CallStack stack;
stack.update();
stack.dump("");
}
}
and add lib setting to to Android.mak since CallStack.tpp is in libutils
LOCAL_SHARED_LIBRARIES += libutils
but I always get error with message:
error: undefined reference to 'android::CallStack::CallStack()'
error: undefined reference to 'android::CallStack::update(int, int)'
...
It seems the executable resolve the symbols at link time rather than load the .so file in runtime?
Do I missing something or there is some limit in Android build system?
I know it is a simple question, but I really need help...
update1
I try to add the code to another executable. The result is same... Does anyone knows the rule of android build system?
update2
There are some key words in my console "target StaticExecutable: ...", I think is is the answer.
http://en.wikipedia.org/wiki/Static_executable

my final target is to dump user space stack.
after google so many information from internet, I found there are 4 ways:
ptrace： http://en.wikipedia.org/wiki/Ptrace
It is really hard to use ptrace, and we need to stop the thread before using ptrace to attach
_unwind_backtrace: the way used by CallStack (CallStack class in CallStack.cpp)
example: http://git.stlinux.com/?p=stm/uclibc.git;a=blob;f=libubacktrace/sysdeps/sh/backtrace.c;h=18b91b1bb3fa26344a521927c631553a410fcf56;hb=d6a3d9ece5922a337800a8e2ed4db7e226f9ccb3
It is work with a drawback: if you use it as the thread is processing signal, it would dump signal stack rather than dump thread stack
The same problen: How to get fullstacktrace using _Unwind_Backtrace on SIGSEGV
backtrace: http://www.gnu.org/software/libc/manual/html_node/Backtraces.html
a GNU extension function, not be implemented in Bionic libc used by Android
reference: https://stackoverflow.com/a/8295238/1442443
reference: http://lists.puredata.info/pipermail/pd-list/2012-02/094258.html
a patch to dump user space thread stack: http://www.gossamer-threads.com/lists/linux/kernel/1525096
but only be implemented in X86 architecture... orz
I try to port it to android, no it only shows the first frame of stack since arm does not use frame pointer.
So... 2 is the answer.
However, I wonder if someone can resolve the problem : How to get fullstacktrace using _Unwind_Backtrace on SIGSEGV
update:
if you can use cross compiler to use glic to compile your code, maybe you can use 3. backtrace !
http://communities.mentor.com/community/cs/archives/arm-gnu/msg02514.html
update2
a good article
http://codingrelic.geekhold.com/2009/05/pre-mortem-backtracing.html

Since this is such an important question here is my answer that worked for me. My code is in C so it has to call a C++ function that can access android::CallStack.
stackdump.cpp:
#include < utils/CallStack.h >
extern "C" void dumpCallStack( char *label)
{
android::CallStack cs;
cs.update();
cs.dump(label);
}
my main code (foo.c):
void dumpCallStack(char *label);
...
dumpCallStack(\__FUNCTION__);

I have had the same problem once. And it is hard to interpret.
The syntax is of course correct and reasonable!
I have tried many methods but it did not work.
Finally, I got an idea that, the lib reference "LOCAL_SHARED_LIBRARIES += libutils" should be put into a makefile generating a dynamic library rather than into a makefile generating a static library. This is the final reason.
Reference:
http://yongbingchen.github.io/blog/2013/05/09/dump-stack-in-android-native-c-code/

I also received this error, but I added:
LOCAL_STATIC_LIBRARIES += libutils
before line of LOCAL_MODULE := xxx in vm/Android.m of three targets and added
LOCAL_SHARED_LIBRARIES += libcorkscrew
in vm/Android.mk
and libdex/Android.mk, and same for the dexlist/Android.mk, dexdump/Android.mk
After all these done, it works for me.

How to print log messages with in Android framework

I am trying to print log messages within core Android framework files. For example, I tried logging messages within MediaRecorderClient.cpp under frameworks\base\media\libmediaplayerservice\. I've tried LOGV, LOGE, LOGD, printf, and __android_log_print, without any success.
Which command should I use to print log messages?

Log should be used, but it will print to logcat not system print.
Example:
Log.d("filter", example text); // filter is any tag you want to use as filter
You can open logcat in eclipse from window-show view -> other -> android -> logcat

What kind of error do you receive? If it does not compile, make sure you've included <android/log.h>, also in Android.mk:
LOCAL_LDLIBS := -llog
If it compiles but does not produce any output, then, like #Warpzit has said, you have to look at logcat to see your messages.

It also seems that you can only pass a char* to the JNI LOG methods. So if you have numbers in your debug string, you have to put them into a char buffer (with sprintf).

/system/core/include/cutils/log.h defines the macros for logging in the Android Framework.
So you uncomment the line that says #define LOG_NDEBUG 0 at the top of the source file and it will enable VERBOSE logging. You will need to recompile that entire library and put it into your android system.img build.
I believe the macro calls are ALOGV, ALOGE and so on.
It is similar to this other answer:
How to get Verbose logging in logcat for a specific module

First declare string
Private String Tag = getClass().getsimplename();
and than in your method
Log.d(Tag,"This is my oncreate method");

Eclipse: Problems with JNI code debugging

Background
I'm writing application for android, using Eclipse in Windows. I'm implementing C code in JAVA and for that I'm using JNI. I have many functions and my problem is that I want to debug functions in JNI.
Question
Can I debug my code which is written in JNI in C language ?

Here is answer How to start logging for Android NDK !
Some weeks I was researching how I can write logs in Eclipse from Android NDK code. I found some examples in Internet and want to share it with you. Following steps below you can start logging on Eclipse.
Include log.h file into your Android NDK source file
#include <android/log.h>
Add the line below to your Android.mk make file.
LOCAL_LDLIBS := -llog
Now you can start logging, this two steps allows you to write logs in Eclipse from Android NDK. Write the line below in your Android NDK code and the log will bw appear in the Eclipse
__android_log_write(ANDROID_LOG_ERROR,"Tag","Message");
use following Flags to write logs in the column which you want.
typedef enum android_LogPriority {
ANDROID_LOG_UNKNOWN = 0,
ANDROID_LOG_DEFAULT, /* only for SetMinPriority() */
ANDROID_LOG_VERBOSE,
ANDROID_LOG_DEBUG,
ANDROID_LOG_INFO,
ANDROID_LOG_WARN,
ANDROID_LOG_ERROR,
ANDROID_LOG_FATAL,
ANDROID_LOG_SILENT, /* only for SetMinPriority(); must be last */
} android_LogPriority
For example if you want to write in Info column you must write
__android_log_write(ANDROID_LOG_INFO,"Tag","Message");
So, Good Luck !