Android链接器:对bsd_signal的未定义引用 [英] Android linker: undefined reference to bsd_signal
问题描述
我正在运行gradlew来编译具有静态lib依赖项的Android应用.不知何故，我对bsd_signal有未定义的引用.
I'm running gradlew to compile an Android app that has a static lib dependency. Somehow, I have an undefined reference to bsd_signal.
我能够使用gradle 1.X编译该应用程序，但是我不得不切换到gradle 2.10并删除我的Android.mk文件，以便将更多的构建指令放入我的gradle.build文件中，并且这就是麻烦所在.
I was able to compile this app with gradle 1.X, but I've been obliged to switch to gradle 2.10 and to drop my Android.mk file in favour of putting more build instruction into my gradle.build file, and this is where the trouble arises.
有人可以告诉我是否有定义bsd_signal的库，该库应该链接到我的项目吗?
Can anyone tell me whether there is a library that defines bsd_signal, which I should link to my project?
编译器输出
Starting process 'command '/home/myself/Android/Sdk/ndk-bundle/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-g++''. Working directory: /home/myself/projects/DroidEar/app Command: /home/myself/Android/Sdk/ndk-bundle/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-g++ @/home/myself/projects/DroidEar/app/build/tmp/linkNativeArmeabi-v7aDebugSharedLibrary/options.txt
Successfully started process 'command '/home/myself/Android/Sdk/ndk-bundle/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-g++''
/android/ndk/platforms/android-9/arch-arm/usr/include/signal.h:113: error: undefined reference to 'bsd_signal'
/android/ndk/platforms/android-9/arch-arm/usr/include/signal.h:113: error: undefined reference to 'bsd_signal'
collect2: error: ld returned 1 exit status
TMI:这是我的gradle.build文件
apply plugin: 'com.android.model.application'
model {
repositories {
libs(PrebuiltLibraries) {
Superpowered {
binaries.withType(StaticLibraryBinary) {
def prefix = "src/main/jniLibs/Superpowered"
headers.srcDir "${prefix}"
if (targetPlatform.getName() == "armeabi-v7a")
staticLibraryFile = file("${prefix}/libSuperpoweredAndroidARM.a")
else if (targetPlatform.getName() == "arm64-v8a")
staticLibraryFile = file("${prefix}/libSuperpoweredAndroidARM64.a")
else if (targetPlatform.getName() == "x86_64")
staticLibraryFile = file("${prefix}/libSuperpoweredAndroidX86_64.a")
else if (targetPlatform.getName() == "X86")
staticLibraryFile = file("${prefix}/libSuperpoweredAndroidX86.a")
}
}
}
}
android {
compileSdkVersion = 23
buildToolsVersion = "23.0.3"
sources {
main {
jni {
dependencies {
library "Superpowered" linkage "static"
}
}
}
}
ndk {
ldLibs.addAll(['log', 'android', 'c'])
}
defaultConfig {
applicationId = "edu.ucdavis.auditoryenhancer"
minSdkVersion.apiLevel = 22
targetSdkVersion.apiLevel = 23
versionCode = 1
versionName = "1.0"
}
}
android.ndk {
moduleName = "native"
}
android.buildTypes {
release {
minifyEnabled = false
proguardFiles.add(file("proguard-rules.pro"))
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
}
在我看来，bsd_signal是在platforms/android-9/arch-x86/usr/lib/libc.a的signal.o组件中定义的，但是即使使用上述包含c的ldLibs调用，我仍然会收到错误.
It looks to me like bsd_signal is defined in the signal.o component of platforms/android-9/arch-x86/usr/lib/libc.a, but even with my ldLibs call above including c, I get the error.
推荐答案
直到 android-19 包含在内的NDK-s signal.h声明为bsd_signal extern 和bsd_signal.
Till android-19 inclusive NDK-s signal.h declared bsd_signal extern and signal was an inline calling bsd_signal.
以 android-21 开头的signal是 extern ，而根本没有声明bsd_signal.
Starting with android-21 signal is an extern and bsd_signal is not declared at all.
有趣的是，bsd_signal在 NDK r10e android-21 libc.so中仍然可以作为符号使用(因此，如果使用 r10e ，则不会出现链接错误)，但在 NDK r11 及更高版本中不可用.
What's interesting, bsd_signal was still available as a symbol in NDK r10e android-21 libc.so (so there were no linking errors if using r10e), but is not available in NDK r11 and up.
如果将用 android-21 + 构建的代码与静态库链接，则从NDK-s android-21 + libc.so中删除bsd_signal会导致链接错误.使用较低的NDK级别(称为signal或bsd_signal)构建.调用signal的最受欢迎的库是 OpenSSL .
Removing of bsd_signal from NDK-s android-21+ libc.so results in linking errors if code built with android-21+ is linked with static libs built with lower NDK levels that call signal or bsd_signal. Most popular library which calls signal is OpenSSL.
警告:使用 android-21 + 构建静态库(会直接放置signal符号)会很好地链接，但会导致*.so失败由于在libc.so中找不到signal符号，因此可以在较旧的Android OS设备上加载.
WARNING: Building those static libs with android-21+ (which would put signal symbol directly) would link fine, but would result in *.so failing to load on older Android OS devices due to signal symbol not found in theirs libc.so.
因此，对于任何调用signal或bsd_signal的代码，最好坚持使用< = android-19 .
Therefore it's better to stick with <=android-19 for any code that calls signal or bsd_signal.
要链接使用< android-21 构建的库，我最终声明了一个bsd_signal包装器，该包装器将从libc.so调用bsd_signal(在设备的libc.so中仍然可用，甚至不超过Android 7.0).
To link a library built with <android-21 I ended up declaring a bsd_signal wrapper which would call bsd_signal from libc.so (it's still available in device's libc.so, even up to Android 7.0).
#if (__ANDROID_API__ > 19)
#include <android/api-level.h>
#include <android/log.h>
#include <signal.h>
#include <dlfcn.h>
extern "C" {
typedef __sighandler_t (*bsd_signal_func_t)(int, __sighandler_t);
bsd_signal_func_t bsd_signal_func = NULL;
__sighandler_t bsd_signal(int s, __sighandler_t f) {
if (bsd_signal_func == NULL) {
// For now (up to Android 7.0) this is always available
bsd_signal_func = (bsd_signal_func_t) dlsym(RTLD_DEFAULT, "bsd_signal");
if (bsd_signal_func == NULL) {
// You may try dlsym(RTLD_DEFAULT, "signal") or dlsym(RTLD_NEXT, "signal") here
// Make sure you add a comment here in StackOverflow
// if you find a device that doesn't have "bsd_signal" in its libc.so!!!
__android_log_assert("", "bsd_signal_wrapper", "bsd_signal symbol not found!");
}
}
return bsd_signal_func(s, f);
}
}
#endif
PS.看起来bsd_signal符号将在 NDK r13 中返回到libc.so:
PS. Looks like the bsd_signal symbol will be brought back to libc.so in NDK r13:
https://github.com/android-ndk/ndk/issues/160#issuecomment-236295994
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