This question was migrated from Android Enthusiasts Stack Exchange because it can be answered on Stack Overflow.
Migrated 13 days ago.
If I have an ELF binary written in C and compiled using an Android NDK, is there an API for logging messages so that they show up in logcat?
Yes. This can be done by including
#include <android/log.h>
and calling
int __android_log_print(
int prio,
const char *tag,
const char *fmt,
...
);
You can even set the default tag via
void __android_log_set_default_tag(
const char *tag
);
This way, you can pull NULL as the tag in __android_log_print.
You'll have to add -llog to your linker flags.
Related
I am new to the android studio, could you please help me, I tried multiple time to print Logcats on Android emulator but unable to see Logcats print.Is there any possibility to print on Android emulator console by using Native code prints and also How to print Logcats on android studio logcat window using normal C printf.
I tried this one,
#include <stdio.h>
#include <android/log.h>
#define LOGD(...) __android_log_print(int prio, const char *tag, const char *fmt, ...)
int main()
{
int a=23;
LOGD(ANDROID_LOG_DEBUG,"Print something %d",a);
return 0;
}
I compiled the gRPC Android example from here.
I want to run the program as executable from adb shell.
Added these lines to grpc-helloworld.cc:
#include <iostream>
int main() {
std::cout << "qwerty" << std::endl;
return 0;
}
And these lines to its CMakeLists.txt:
add_executable(avocado
src/main/cpp/grpc-helloworld.cc)
target_include_directories(avocado
PRIVATE ${HELLOWORLD_PROTO_HEADERS})
target_link_libraries(avocado
helloworld_proto_lib
android
${log-lib})
Then I pushed the generated executable and libs file and tried to run it:
LD_LIBRARY_PATH=. ./avocado
I got the following error:
[libprotobuf FATAL
/home/buga/grpc/third_party/protobuf/src/google/protobuf/stubs/common.cc:79]
This program was compiled against version 3.0.0 of the Protocol Buffer
runtime library, which is not compatible with the installed version
(3.5.1). Contact the program author for an update. If you compiled
the program yourself, make sure that your headers are from the same
version of Protocol Buffers as your link-time library. (Version
verification failed in
"out/soong/.intermediates/frameworks/av/drm/libmediadrm/libmediadrm/android_arm64_armv8-a_kryo300_shared_core/gen/proto/frameworks/av/drm/libmediadrm/protos/plugin_metrics.pb.cc".)terminating
with uncaught exception of type google::protobuf::FatalException: This
program was compiled against version 3.0.0 of the Protocol Buffer
runtime library, which is not compatible with the installed version
(3.5.1). Contact the program author for an update. If you compiled
the program yourself, make sure that your headers are from the same
version of Protocol Buffers as your link-time library. (Version
verification failed in
"out/soong/.intermediates/frameworks/av/drm/libmediadrm/libmediadrm/android_arm64_armv8-a_kryo300_shared_core/gen/proto/frameworks/av/drm/libmediadrm/protos/plugin_metrics.pb.cc".)
Aborted
What am I doing wrong?
We realized that there is a version of the protobuf library called libprotobuf-cpp-full.so and libprotobuf-cpp-lite.so, and it seems that their version is 3.0.0. This is conflicting with our version (3.5.1) which is compiled into either a static lib, or as a shared lib.
I'm not quite sure why this happens. Something about once the linker loads helloworld_proto_lib, it overrides all loaded protobuf symbols, and for some reason another library that you had nothing to do with crashes your program. But that's not telling you anything new.
Here's one way to solve this problem:
1. Changes to grpc-helloworld.cc
Make the main extern "C", and change its name maybe. For example:
extern "C" int my_main() {
std::cout << "qwerty" << std::endl;
return 0;
}
2. Add file grpc-avocado.cc
This will contain the actual main of the executable, which will dynamically load the libraries helloworld_proto_lib and grpc-helloworld. Here's how to do it:
#include <iostream>
#include <android/dlext.h>
#include <dlfcn.h>
int main() {
android_dlextinfo extinfo;
extinfo.flags = ANDROID_DLEXT_FORCE_LOAD;
void* proto_lib = android_dlopen_ext("/path/to/libhelloworld_proto_lib.so", RTLD_LAZY, &extinfo);
void* helloworld = dlopen("/path/to/libgrpc-helloworld.so", RTLD_LAZY);
int (*my_main)() = (int (*)())dlsym(helloworld, "my_main");
return my_main();
}
The function android_dlopen_ext from #include <android/dlext.h>, and its flag argument, are described here: https://developer.android.com/ndk/reference/group/libdl . In the above code we pass the flag ANDROID_DLEXT_FORCE_LOAD, which is documented as:
When set, do not use stat(2) to check if the library has already been loaded.
This flag allows forced loading of the library in the case when for some reason multiple ELF files share the same filename (because the already-loaded library has been removed and overwritten, for example).
Note that if the library has the same DT_SONAME as an old one and some other library has the soname in its DT_NEEDED list, the first one will be used to resolve any dependencies.
I think the text in bold is what explains why this solution works.
3. Change CMakeLists.txt
Since you'll be loading helloworld_proto_lib dynamically, you can now remove it from the executable definition, and there's no need for any proto headers:
add_executable(avocado
src/main/cpp/grpc-avocado.cc)
target_link_libraries(avocado
android
${log-lib})
Build, push, and run
You can now build, push the executable avocado and the two libraries libgrpc-helloworld.so, libhelloworld_proto_lib.so, and run. You don't need LD_LIBRARY_PATH. Good luck with the rest of your project!
I've just installed the NDK onto Eclipse, but I'm having some trouble with something..
Here's the code:
#include <jni.h>
#include <stdlib.h>
#include <stdio.h>
void deleteFile(const char *fileName) {
remove(fileName);
}
void writeFile(const char *fileName, byte array) {
}
But something is going wrong.. I got this error:
jni/[projectName].cpp:9:38: error: 'byte' has not been declared
byte couldn't be resolved! which is a big problem because I absolutely need that type.. I have to use it to write data into a file!
I've followed a lot of tutorials, I also tried to import all of my MinGW libraries with no success.
byte isn't a standard C or C++ type ... It may be a typedef in a non-standard header file. Where have you seen code with that type ? May be you would like to use const unsigned char * ?
I know that Visual Studio define BYTE type:
typedef unsigned char BYTE; // 8-bit unsigned entity.
typedef BYTE * PBYTE; // Pointer to BYTE.
But this is not standard. And it is "BYTE", not "byte".
'byte' doesn't exist in standard C or C++, if all your code depends on , use 'jbyte' instead, it is defined in this header, and maps to an 8-bit unsigned integer type.
Alternatively, you could define 'byte' with a typedef as in:
typedef unsigned char byte;
And ensure this is used/parsed by all your sources (e.g. put it in a shared header).
A slightly more correct way to do it is:
#include <inttypes.h>
typedef uint8_t byte;
It will be equivalent on all supported Android platforms, but requires an additional include.
(Technically, 'char' can be more than 8 bits on some really odd platforms, but none of them are ever going to be targetted by Android).
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:
ptraceļ¼ 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.
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 !