android - 为什么C++可执行文件在Android设备上找不到动态库

Question

我正在使用 NDK 为 android 构建一个 C++ 可执行文件。可执行(./main)源文件 main.c 非常简单:

#include <stdio.h>
#include <stdlib.h>
int main()
{
     printf("Hello World\n");
     return 0;
}

我可以使用 cmake 和 android-cmake-toolchain 构建它。之后我把它放在 Android 设备上:

# this script is used to put binary to the device
import subprocess

output_executable = 'libs/armeabi-v7a/main  /data/local/tmp/main'

# step 1: push
push_cmd = 'adb push '+output_executable
subprocess.check_call(push_cmd,stderr=subprocess.STDOUT, shell=True)

# step 2: change mode
mod_cmd = 'adb shell chmod 777 '+output_executable
subprocess.check_call(mod_cmd,stderr=subprocess.STDOUT, shell=True)

# step 3: run the program
run_cmd = 'adb shell '+output_executable
subprocess.check_call(run_cmd,stderr=subprocess.STDOUT, shell=True)

一切正常。但是，如果我只是把main.c改成main.cpp，然后照着做，编译就没问题了。但是当它放在 Android 设备上时，我收到以下错误消息:

soinfo_link_image(linker.cpp:1635): could not load library "libgnustl_shared.so" needed by "/data/local/tmp/main"; ....

我觉得应该根据报错提示指出STL库在Android平台的位置。任何想法将不胜感激。

Answer 1

.cpp 扩展使 NDK build 使用 c++ 编译器并与一些 c++ 库链接。您应该使用 -nodefaultlibs 选项并明确定义要链接的库。

另外，看看 SO: g++, static initialization and -nostdlib .

更新。

添加了日志(针对非信徒)。

当文件有 .c 扩展名时:

C:\Dev\Projects\NdkTest\jni>ndk-build -B V=1 

[armeabi] Compile thumb : hello-jni <= main.c

C:/Dev/Tools/Android/ndk-r10d/toolchains/arm-linux-androideabi-4.8/pre 
built/windows-x86_64/bin/arm-linux-androideabi-gcc -MMD -MP -MF 
C:\Dev\Projects\NdkTest/ob j/local/armeabi/objs/hello-jni/main.o.d 
-fpic -ffunction-sections -funwind-tables -fstack-protector 
-no-canonical-prefixes -march=armv5te -mtune=xscale -msoft-f loat 
-mthumb -Os -g -DNDEBUG -fomit-frame-pointer -fno-strict-aliasing 
-finline-limit=64 -IC:\Dev\Projects\NdkTest/jni -DANDROID 
-Wa,--noexecstack -Wformat -We rror=format-security 
-IC:/Dev/Tools/Android/ndk-r10d/platforms/android-3/arch-arm/usr/inclu 
de -c C:\Dev\Projects\NdkTest/jni/main.c -o C:\Dev\Projects\NdkTe 
st/obj/local/armeabi/objs/hello-jni/main.o 

[armeabi] Executable : hello-jni 

C:/Dev/Tools/Android/ndk-r10d/toolchains/arm-linux-androideabi-4.8/pre 
built/windows-x86_64/bin/arm-linux-androideabi-g++ -Wl,--gc-sections 
-Wl,-z,nocopyreloc -- 
sysroot=C:/Dev/Tools/Android/ndk-r10d/platforms/android-3/arch-arm 
-Wl,-rpath-link=C:/Dev/Tools/Android/ndk-r10d/platforms/android-3/arch 
-arm/usr/lib -Wl,-rpath 
-link=C:\Dev\Projects\NdkTest/obj/local/armeabi 
C:\Dev\Projects\NdkTest/obj/local/armeabi/objs/hello-jni/main.o -lgcc 
-no-canonical-prefixes -Wl,--no-undefined -Wl,-z,noexecstack 
-Wl,-z,relro -Wl,-z,now -mthumb -lc -lm -o 
C:\Dev\Projects\NdkTest/obj/local/armeabi/hello-jni 

[armeabi] Install : hello-jni => libs/armeabi/hello-jni 

copy /b/y "C:\Dev\Projects\NdkTest\obj\local\armeabi\hello-jni" 
"C:\Dev\Projects\NdkTest\libs\armeabi\hello-jni" > NUL 
C:/Dev/Tools/Android/ndk-r10d/toolchains/arm-linux-androideabi-4.8/pre 
built/windows-x86_64/bin/arm-linux-androideabi-strip --strip-unneeded 
C:\Dev\Projects\Ndk Test/libs/armeabi/hello-jni 

当文件有 .cpp 扩展名时:

C:\Dev\Projects\NdkTest\jni>ndk-build -B V=1 

[armeabi] Compile++ thumb: hello-jni <= main.cpp

C:/Dev/Tools/Android/ndk-r10d/toolchains/arm-linux-androideabi-4.8/pre 
built/windows-x86_64/bin/arm-linux-androideabi-g++ -MMD -MP -MF 
C:\Dev\Projects\NdkTest/ob j/local/armeabi/objs/hello-jni/main.o.d 
-fpic -ffunction-sections -funwind-tables -fstack-protector 
-no-canonical-prefixes -march=armv5te -mtune=xscale -msoft-f loat 
-fno-exceptions -fno-rtti -mthumb -Os -g -DNDEBUG -fomit-frame-pointer 
-fno-strict-aliasing -finline-limit=64 
-IC:/Dev/Tools/Android/ndk-r10d/sources/cxx-s tl/system/include 
-IC:\Dev\Projects\NdkTest/jni -DANDROID -Wa,--noexecstack -Wformat 
-Werror=format-security -IC:/Dev/Tools/Android/ndk-r10d/platforms/and 
roid-3/arch-arm/usr/include -c C:\Dev\Projects\NdkTest/jni/main.cpp -o 
C:\Dev\Projects\NdkTest/obj/local/armeabi/objs/hello-jni/main.o 

[armeabi] StaticLibrary : libstdc++.a 

C:/Dev/Tools/Android/ndk-r10d/toolchains/arm-linux-androideabi-4.8/pre 
built/windows-x86_64/bin/arm-linux-androideabi-gcc-ar crsD 
C:\Dev\Projects\NdkTest/obj/loc al/armeabi/libstdc++.a 

[armeabi] Executable : hello-jni 

C:/Dev/Tools/Android/ndk-r10d/toolchains/arm-linux-androideabi-4.8/pre 
built/windows-x86_64/bin/arm-linux-androideabi-g++ -Wl,--gc-sections 
-Wl,-z,nocopyreloc -- 
sysroot=C:/Dev/Tools/Android/ndk-r10d/platforms/android-3/arch-arm 
-Wl,-rpath-link=C:/Dev/Tools/Android/ndk-r10d/platforms/android-3/arch 
-arm/usr/lib -Wl,-rpath 
-link=C:\Dev\Projects\NdkTest/obj/local/armeabi 
C:\Dev\Projects\NdkTest/obj/local/armeabi/objs/hello-jni/main.o 
C:\Dev\Projects\NdkTest/obj/local/armeabi/libstd c++.a -lgcc 
-no-canonical-prefixes -Wl,--no-undefined -Wl,-z,noexecstack 
-Wl,-z,relro -Wl,-z,now -mthumb 
-LC:/Dev/Tools/Android/ndk-r10d/platforms/android-3/a rch-arm/usr/lib 
-lstdc++ -lc -lm -o 
C:\Dev\Projects\NdkTest/obj/local/armeabi/hello-jni 

[armeabi] Install : hello-jni => libs/armeabi/hello-jni 

copy /b/y "C:\Dev\Projects\NdkTest\obj\local\armeabi\hello-jni" 
"C:\Dev\Projects\NdkTest\libs\armeabi\hello-jni" > NUL 
C:/Dev/Tools/Android/ndk-r10d/toolchains/arm-linux-androideabi-4.8/pre 
built/windows-x86_64/bin/arm-linux-androideabi-strip --strip-unneeded 
C:\Dev\Projects\Ndk Test/libs/armeabi/hello-jni 

如您所见，将文件扩展名重命名为 .cpp 使 ndk-build 使用不同的编译器并链接到其他库。

更新 2.

1) 如果您不需要gnuSTL_shared，请更新您的Android.mk

LOCAL_CXXFLAGS += -nostdinc++ -I...
LOCAL_LDFLAGS += -nodefaultlibs -L...
LOCAL_LDLIBS += lc -lm -ldl -l...

2) 如果您确实需要 gnuSTL_shared，请更新您的部署脚本

import subprocess

output_dir = 'libs/armeabi-v7a/'
output_files = ['main', 'libgnustl_shared.so']
target_dir = '/data/local/tmp/'
target_executable = target_dir+'main'

# step 1: push
for f in output_files:
    push_cmd = 'adb push '+output_dir+f+' '+target_dir+f
    subprocess.check_call(push_cmd,stderr=subprocess.STDOUT, shell=True)

# step 2: change mode
mod_cmd = 'adb shell chmod 777 '+target_executable
subprocess.check_call(mod_cmd,stderr=subprocess.STDOUT, shell=True)

# step 3: run the program
run_cmd = 'adb shell LD_LIBRARY_PATH='+target_dir.rstrip('/')+':$LD_LIBRARY_PATH '+target_executable
subprocess.check_call(run_cmd,stderr=subprocess.STDOUT, shell=True)

为什么要更新 LD_LIBRARY_PATH 请参阅 SO: Android – how to load shared library?