I am trying to link my c-program to a shared object library (libfoo.so) using the ARM cross-compiler arm-linux-gnueabi-gcc. I am compiling on a Ubuntu system, and I want to run the program on an Android device. The compiling works, but when I try to run the program on my android device I get an error.
I've created a simple test program containing the following files:
foo.c:
#include <stdio.h>
void foo(void){ puts("Hello, I am a shared library"); }
foo.h:
#ifndef foo_h__
#define foo_h__
extern void foo(void);
#endif
main.c:
#include <stdio.h>
#include "foo.h"
int main(void)
{
puts("This is a shared library test...");
foo();
return 0;
}
I have then created the shared object library using:
arm-linux-gnueabi-gcc -c -fPIC foo.c
arm-linux-gnueabi-gcc -shared -o libfoo.so foo.o
I then compile my program using:
arm-linux-gnueabi-gcc -L/home/foo -o test main.c -lfoo
After uploading the test-program to the Android device using adb, I am not able to run it. Instead I get the error: /system/bin/sh: ./test: No such file or directory
I am in the right directory and the test-file is present, so I assume that it is the shared library that cannot be found. I've tried uploading libfoo.so to the android device as well (to the same path as specified when compiling), but it still doesn't work to run the program.
I've gotten it to work with a static library (foo.o) using arm-linux-gnueabi-gcc -static -o test main.c foo.o, but not with a shared library.
How do I properly link a shared library when cross-compiling, to make sure that the program can then run on an Android device?
The linker isn't able to dynamically link to the library.
Define LD_LIBRARY_PATH environment variable to include the library:
export LD_LIBRARY_PATH=/home/foo
Related
I'm having an Error in my Native C++ Code in Android NDK Application
My main.cpp
#include <stdio.h>
int main()
{
printf("Hello, world\n");
return 0;
}
The main.c is exactly the same.
If i run
/home/rip/Music/android-ndk-r19b/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android26-clang -pie main.c
then
adb push a.out /data/local/tmp
and
adb shell /data/local/tmp/a.out
all works fine. But if i run
/home/rip/Music/android-ndk-r19b/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android26-clang++ -pie main.cpp
then
adb push a.out /data/local/tmp
and
adb shell /data/local/tmp/a.out
The error message is:
CANNOT LINK EXECUTABLE "/data/local/tmp/a.out": library "libc++_shared.so" not found
Then i tried to run
/home/rip/Music/android-ndk-r19b/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android26-clang++ -pie hello1.cpp /home/rip/Music/android-ndk-r19b/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/aarch64-linux-android/libc++_shared.so
to link the library, but it doesn't work anyway.
The error message is:
CANNOT LINK EXECUTABLE "/data/local/tmp/a.out": library "libc++_shared.so" not found
That's the expected behavior. Unlike the standard C library (to which your program is linking when building with simple *-clang), C++ is not a system library. You have to make it available on the device just like any other third party library.
Quoted from official documentation:
Note: libc++ is not a system library. If you use libc++_shared.so, it must be included in your APK. If you're building your application with Gradle this is handled automatically.
And:
If you're using clang directly in your own build system, clang++ will use c++_shared by default. To use the static variant, add -static-libstdc++ to your linker flags.
So either link with C++ statically by passing -static-libstdc++ to compiler. Or copy the libc++_shared.so (from <NDK>/sources/cxx-stl/llvm-libc++/libs/arm64-v8a/ in your case) and run like:
adb push a.out libc++_shared.so /data/local/tmp/
adb shell
cd /data/local/tmp/
LD_LIBRARY_PATH=. ./a.out
Other than the LLVM's Standard C++ library discussed above, there's also a limited system C++ runtime (/system/lib(64)/libstdc++.so) which "provides support for the basic C++ Runtime ABI". But "The system STL will be removed in a future NDK release."
I compiled the same "hello world" code in a .c and .cpp file and didn't have the same issue when I pushed the application to my device. I assume you're having the same issue as in this topic:
Application can't find libc++_shared.so
The issue may come from your toolchain or toolchain parameters as you are calling clang manually.
I created a simple project that you can run and test:
android-ndk-example
add_executable( # Sets the name of the library.
ndk_example_c
# Provides a relative path to your source file(s).
main.c
)
add_executable( # Sets the name of the library.
ndk_example_cpp
# Provides a relative path to your source file(s).
main2.cpp
)
In generated cmake script, I can see the following definition for cpp compiler:
rule CXX_COMPILER__ndk_example_cpp
depfile = $DEP_FILE
deps = gcc
command = D:\Users\$USER\AppData\Local\Android\Sdk\ndk-bundle\toolchains\llvm\prebuilt\windows-x86_64\bin\clang++.exe --target=armv7-none-linux-androideabi19 --gcc-toolchain=D:/Users/$USER/AppData/Local/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/windows-x86_64 --sysroot=D:/Users/$USER/AppData/Local/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/windows-x86_64/sysroot $DEFINES $INCLUDES $FLAGS -MD -MT $out -MF $DEP_FILE -o $out -c $IN_ABS
description = Building CXX object $out
I write a new Answer for the Solution because i cannot edit my question.
The Solution is the following command for android devices with armv7:
/home/tony/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=armv7-none-linux-androideabi19 --gcc-toolchain=/home/tony/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64 --sysroot=/home/tony/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot main.cpp
For aarch64 armv8 the command is:
/home/tony/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=aarch64-none-linux-android21 --gcc-toolchain=/home/tony/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64 --sysroot=/home/tony/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot main.cpp
A CMakeLists.txt file should look as:
cmake_minimum_required(VERSION 3.1)
set(CMAKE_CXX_COMPILER /home/tony/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++)
project(Test CXX)
set(CMAKE_CXX_FLAGS "--target=aarch64-none-linux-android21 --gcc-toolchain=/home/tony/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64 --sysroot=/home/tony/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/sysroot")
set(SOURCES
main.cpp
)
add_executable(Test ${SOURCES})
Then can the app build with
cmake
make
adb push Test /data/local/tmp
adb shell /data/local/tmp/Test
I've two files:
lib.c
#include<stdio.h>
void hi() {
printf("Hi i'm a library function in lib.so\n");
}
and main.c
#include<stdio.h>
#include<dlfcn.h>
/* based on Jeff Scudder's code */
int main() {
void *SharedObjectFile;
void (*hi)();
// Load the shared libary;
SharedObjectFile = dlopen("./lib.so", RTLD_LAZY);
// Obtain the address of a function in the shared library.
ciao = dlsym(SharedObjectFile, "hi");
// Use the dynamically loaded function.
(*hi)();
dlclose(SharedObjectFile);
}
And I've tried to build an executables using the following commands:
export LD_LIBRARY_PATH=pwd
gcc -c -fpic lib.c
gcc -shared -lc -o lib.so lib.o
gcc main.c -ldl
And it works pretty well.
Then I've tried to export my program on Android (Nexus One, with ARM-v7-0a arch) using the following commands:
export LD_LIBRARY_PATH=pwd
arm-none-linux-gnueabi-gcc -c -fpic lib.c
arm-none-linux-gnueabi-gcc -shared -lc -o lib.so lib.o
arm-none-linux-gnueabi-gcc main.c -ldl -o main
adb push main /system/app
The result of executing ./main on the correct folder on my smartphone is just:
./main: not found
even if my file is right there!
Am I missing anything during the cross-compile process? Any help?
I'm using the cross-compiler from CodeSourcery and it works well for static programs without .so libraries.
Thanks
EDIT: as Igor states below, that was a linker issue. This command fixes it:
arm-none-linux-gnueabi-gcc -o test main.c -Wl,--dynamic-linker=/system/bin/linker -ldl
in my very case I need other libraries because in /system/lib/ there are no many .so files.
The "not found" message refers not to the shared object but to the dynamic linker. Linux uses /lib/ld-linux.so.2 (or /lib64/ld-linux-x86-64.so.2 for x64) while Android uses /bin/linker. You can check which dynamic loader your program uses with readelf -l, e.g.:
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
PHDR 0x000034 0x08048034 0x08048034 0x00100 0x00100 R E 0x4
INTERP 0x000134 0x08048134 0x08048134 0x00013 0x00013 R 0x1
[Requesting program interpreter: /lib/ld-linux.so.2]
You can specify a linker to use with ld's --dynamic-linker switch, but there are likely to be other differences. For example, Android uses a stripped-down libc implementation called bionic, and it may be missing functionality that your program relies on, or have different behavior.
You should use NDK or another Android-targeted toolchain when compiling programs for Android. Even though it's based on Linux kernel, the differences are large enough that Linux-targeted toolchains are not sufficient.
All discussions are for x86.
If I wrote a simple hello program such as the one below:
#include <stdio.h>
int main(){
printf("Hello\n");
return 0;
}
And compile it on my PC with ubuntu
$gcc -shared -mPIC -o hello_new hello.c
Then it will give me segmentation fault when I try to execute hello_new. Same error when I move this binary to an android phone. (But I can compile it as a binary with statically linked libc and run it on the android phone)
Yes, I want to execute a shared object directly.
The reason is below:
I recently get a linux file compiled by someone else. When I use linux command file and readelf to analyze the file. It says it is a shared object (32-bit, compiled with -m32). But I can execute the shared object like an executable in android on a phone:
$./hello
This really confuses me. This shared object file contains printf function calls, not sure if it is statically link or dynamically linked. But since it can run on Android through ADB, I assume it is statically linked against libc.
What kind of compilation technique can allow one to execute shared object directly?
It happens that I am currently working on this type of thing.
One of the main differences between executables and shared object under linux, is that an executable has an interpreter and a (valid) entry point.
For example, on a minimal program :
$ echo 'int main;' | gcc -xc -
If you look at it's elf program headers:
$ readelf --program-headers a.out
...
INTERP 0x0000000000000200 0x0000000000400200 0x0000000000400200
0x000000000000001c 0x000000000000001c R 1
[Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
...
The interpreter program is responsible of the execution of the program, to achieve this, it will perform some initializations like loading the needed shared objects. In fact, it is quite analogous to a script shebang, but for elf files.
In this case, /lib64/ld-linux-x86-64.so.2 is the loader for amd64. You can have multiples loaders: e.g., one for 32bits, one for 64.
Now the entry point :
$ readelf --file-header a.out
ELF Header:
...
Entry point address: 0x4003c0
...
$ readelf -a a.out | grep -w _start
57: 00000000004003c0 0 FUNC GLOBAL DEFAULT 13 _start
By default, you can see that _start is defined as the entry point.
So if you consider the following minimal example :
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#ifdef INTERPRETER
const char interp[] __attribute__((section(".interp"))) = INTERPRETER;
#endif /* INTERPRETER */
void entry_point(void) {
fprintf(stderr, "hello executable shared object world !\n");
_exit(EXIT_SUCCESS);
}
If you compile it as a "normal" shared object and execute it :
$ gcc libexecutable.c -Wall -Wextra -fPIC -shared -o libexecutable.so
$ ./libexecutable.so
Erreur de segmentation
You can see it segfaults. But now if you define an interpreter (adapt it's path to what readelf --program-headers gave you before) and tell to the linker what is your entry point :
$ gcc libexecutable.c -Wall -Wextra -fPIC -shared -o libexecutable.so -DINTERPRETER=\"/lib64/ld-linux-x86-64.so.2\" -Wl,-e,entry_point
$ ./libexecutable.so hello executable shared object world !
now it works. Please note that the _exit() call is necessary to avoid a segfault at the end of the execution.
But in the end, remember that because you specify a custom entry point, you will bypass libc initialization steps which could be needed or not, depending on your needs.
I think your android and pc boths are x86 or arm at the same time, else executable should not run in both platform. Now to make a shared library executable at the same time you can use -pie command line option of gcc. Details can be found in this answer.
now, i have a question: first of all i already get the ndk standalone tool chain ---arm-linux-androideabi-g++ sucessful; now i have to write a commandline c++ program which will use libcurl to do http requests, i can successful compile it on my mac( which has the libcurl default? ) use g++, but when i use the arm-linux-androideabi-g++ to compile it, it produce following error:
arm-linux-androideabi-g++ -std=c++11 -lcurl upload.cpp -o upload
upload.cpp:12:23: fatal error: curl/curl.h: no such file or directory
compilation terminated
i have a libcurl(include files and .a lib file) which can used in android, so howto configure the arm-linux-androideabi-g++ so that it can compile it successfully? thanks advance
I guess you include your header like
#include <curl/curl.h>
if you do that, arm-linux-androideabi-g++ searches header file in some specific location. and if arm-linux-androideabi-g++ does not point same directory with g++, headers can not be found. try to copy just header files of curl to your project, jni/curl folder, and use " instead of <
#include "curl/curl.h"
if you have right .a file, functions in header files will be pointed to lib file successfully.
I've two files:
lib.c
#include<stdio.h>
void hi() {
printf("Hi i'm a library function in lib.so\n");
}
and main.c
#include<stdio.h>
#include<dlfcn.h>
/* based on Jeff Scudder's code */
int main() {
void *SharedObjectFile;
void (*hi)();
// Load the shared libary;
SharedObjectFile = dlopen("./lib.so", RTLD_LAZY);
// Obtain the address of a function in the shared library.
ciao = dlsym(SharedObjectFile, "hi");
// Use the dynamically loaded function.
(*hi)();
dlclose(SharedObjectFile);
}
And I've tried to build an executables using the following commands:
export LD_LIBRARY_PATH=pwd
gcc -c -fpic lib.c
gcc -shared -lc -o lib.so lib.o
gcc main.c -ldl
And it works pretty well.
Then I've tried to export my program on Android (Nexus One, with ARM-v7-0a arch) using the following commands:
export LD_LIBRARY_PATH=pwd
arm-none-linux-gnueabi-gcc -c -fpic lib.c
arm-none-linux-gnueabi-gcc -shared -lc -o lib.so lib.o
arm-none-linux-gnueabi-gcc main.c -ldl -o main
adb push main /system/app
The result of executing ./main on the correct folder on my smartphone is just:
./main: not found
even if my file is right there!
Am I missing anything during the cross-compile process? Any help?
I'm using the cross-compiler from CodeSourcery and it works well for static programs without .so libraries.
Thanks
EDIT: as Igor states below, that was a linker issue. This command fixes it:
arm-none-linux-gnueabi-gcc -o test main.c -Wl,--dynamic-linker=/system/bin/linker -ldl
in my very case I need other libraries because in /system/lib/ there are no many .so files.
The "not found" message refers not to the shared object but to the dynamic linker. Linux uses /lib/ld-linux.so.2 (or /lib64/ld-linux-x86-64.so.2 for x64) while Android uses /bin/linker. You can check which dynamic loader your program uses with readelf -l, e.g.:
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
PHDR 0x000034 0x08048034 0x08048034 0x00100 0x00100 R E 0x4
INTERP 0x000134 0x08048134 0x08048134 0x00013 0x00013 R 0x1
[Requesting program interpreter: /lib/ld-linux.so.2]
You can specify a linker to use with ld's --dynamic-linker switch, but there are likely to be other differences. For example, Android uses a stripped-down libc implementation called bionic, and it may be missing functionality that your program relies on, or have different behavior.
You should use NDK or another Android-targeted toolchain when compiling programs for Android. Even though it's based on Linux kernel, the differences are large enough that Linux-targeted toolchains are not sufficient.