Android构建无法生成32位可执行文件

Question

根据我的第一个问题，我尝试在我的应用程序中包含fanotify.h头。该应用程序基于fsmon (一个小型应用程序，用于使用扇化syscall)，为此我更改了一些代码行，并创建了一个Android.mk makefile：

APP_PLATFORM := android-23
TARGET_PLATFORM := android-23
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

# Enable PIE manually. Will get reset on $(CLEAR_VARS). This
# is what enabling PIE translates to behind the scenes.
LOCAL_CFLAGS += -fPIE -DHAVE_FANOTIFY=1 -DHAVE_SYS_FANOTIFY=0 
LOCAL_LDFLAGS += -fPIE -pie

# give module name
LOCAL_MODULE := fsmon

# include fanotify by api 23:
LOCAL_C_INCLUDES := /home/fabian/Android/Sdk/ndk-bundle/platforms/android-23/arch-arm/usr/include

# include fanotify by sysroot -> 
# LOCAL_C_INCLUDES := /home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/

# list your C files to compile
LOCAL_SRC_FILES := inotify.c fanotify.c util.c main.c

# this option will build executables instead of building library for android application.
include $(BUILD_EXECUTABLE)

我需要包括linux/inotify.h和linux/fanotify.h头。

在执行ndk-build时，只有arm64-v8a、mips64和x86_64可执行文件(在libs/xxx中)被创建，导致以下错误消息：

fabian@fabian-ubuntu:~/kernel_android_goldfish/fsmon/fsmon/jni$ ndk-build 
[arm64-v8a] Compile        : fsmon <= inotify.c
[arm64-v8a] Compile        : fsmon <= fanotify.c
[arm64-v8a] Compile        : fsmon <= util.c
[arm64-v8a] Compile        : fsmon <= main.c
[arm64-v8a] Executable     : fsmon
[arm64-v8a] Install        : fsmon => libs/arm64-v8a/fsmon
[x86_64] Compile        : fsmon <= inotify.c
[x86_64] Compile        : fsmon <= fanotify.c
[x86_64] Compile        : fsmon <= util.c
[x86_64] Compile        : fsmon <= main.c
[x86_64] Executable     : fsmon
[x86_64] Install        : fsmon => libs/x86_64/fsmon
[mips64] Compile        : fsmon <= inotify.c
[mips64] Compile        : fsmon <= fanotify.c
[mips64] Compile        : fsmon <= util.c
[mips64] Compile        : fsmon <= main.c
[mips64] Executable     : fsmon
[mips64] Install        : fsmon => libs/mips64/fsmon
[armeabi-v7a] Compile thumb  : fsmon <= inotify.c
In file included from /home/fabian/kernel_android_goldfish/fsmon/fsmon/jni/inotify.c:9:
In file included from /home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/signal.h:49:
In file included from /home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/linux/signal.h:21:
In file included from /home/fabian/Android/Sdk/ndk-bundle/platforms/android-9/arch-arm/usr/include/asm/signal.h:82:
/home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/asm-generic/signal.h:92:21: error: use of undeclared identifier
      '__BITS_PER_LONG'
  unsigned long sig[_NSIG_WORDS];
                    ^
/home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/asm-generic/signal.h:25:38: note: expanded from macro '_NSIG_WORDS'
#define _NSIG_WORDS (_KERNEL__NSIG / _NSIG_BPW)
                                     ^
/home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/asm-generic/signal.h:24:19: note: expanded from macro '_NSIG_BPW'
#define _NSIG_BPW __BITS_PER_LONG
                  ^
/home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/asm-generic/signal.h:94:3: error: typedef redefinition with different
      types ('struct (anonymous struct at /home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/asm-generic/signal.h:91:9)' vs
      'unsigned long')
} sigset_t;
  ^
/home/fabian/Android/Sdk/ndk-bundle/platforms/android-9/arch-arm/usr/include/asm/signal.h:20:23: note: previous definition is here
typedef unsigned long sigset_t;
                      ^
/home/fabian/Android/Sdk/ndk-bundle/platforms/android-9/arch-arm/usr/include/asm/signal.h:84:8: error: redefinition of 'sigaction'
struct sigaction {
       ^
/home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/asm-generic/signal.h:101:8: note: previous definition is here
struct sigaction {
       ^
In file included from /home/fabian/kernel_android_goldfish/fsmon/fsmon/jni/inotify.c:9:
In file included from /home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/signal.h:49:
In file included from /home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/linux/signal.h:21:
/home/fabian/Android/Sdk/ndk-bundle/platforms/android-9/arch-arm/usr/include/asm/signal.h:97:16: error: redefinition of
      'sigaltstack'
typedef struct sigaltstack {
               ^
/home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/asm-generic/signal.h:111:16: note: previous definition is here
typedef struct sigaltstack {
               ^
In file included from /home/fabian/kernel_android_goldfish/fsmon/fsmon/jni/inotify.c:9:
In file included from /home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/signal.h:49:
In file included from /home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/linux/signal.h:21:
/home/fabian/Android/Sdk/ndk-bundle/platforms/android-9/arch-arm/usr/include/asm/signal.h:101:3: error: typedef redefinition with
      different types ('struct (anonymous struct at
      /home/fabian/Android/Sdk/ndk-bundle/platforms/android-9/arch-arm/usr/include/asm/signal.h:97:16)' vs 'struct sigaltstack')
} stack_t;
  ^
/home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/asm-generic/signal.h:116:3: note: previous definition is here
} stack_t;
  ^
In file included from /home/fabian/kernel_android_goldfish/fsmon/fsmon/jni/inotify.c:9:
/home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/signal.h:71:9: warning: 'NSIG' macro redefined [-Wmacro-redefined]
#define NSIG _NSIG
        ^
/home/fabian/Android/Sdk/ndk-bundle/platforms/android-9/arch-arm/usr/include/asm/signal.h:19:9: note: previous definition is here
#define NSIG 32
        ^
In file included from /home/fabian/kernel_android_goldfish/fsmon/fsmon/jni/inotify.c:9:
/home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/signal.h:79:9: warning: 'SIGRTMIN' macro redefined [-Wmacro-redefined]
#define SIGRTMIN (__libc_current_sigrtmin())
        ^
/home/fabian/Android/Sdk/ndk-bundle/platforms/android-9/arch-arm/usr/include/asm/signal.h:58:9: note: previous definition is here
#define SIGRTMIN 32
        ^
In file included from /home/fabian/kernel_android_goldfish/fsmon/fsmon/jni/inotify.c:9:
/home/fabian/Android/Sdk/ndk-bundle/sysroot/usr/include/signal.h:80:9: warning: 'SIGRTMAX' macro redefined [-Wmacro-redefined]
#define SIGRTMAX (__libc_current_sigrtmax())
        ^
/home/fabian/Android/Sdk/ndk-bundle/platforms/android-9/arch-arm/usr/include/asm/signal.h:59:9: note: previous definition is here
#define SIGRTMAX _NSIG
        ^
5 errors generated.
    make: *** [/home/fabian/kernel_android_goldfish/fsmon/fsmon/obj/local/armeabi-v7a/objs/fsmon/inotify.o] Error 1

inotify.c的原因包括重新包含linux/signal.h的signal.h头，而这反过来又包括出现错误的platforms/android-9/arch-arm/usr/include/asm/signal.h。(突然从安卓-9)。

我不知道问题出在哪里。我试图从sysroot中包含包含文件夹，但是也会出现类似的错误。

源文件：inotify.c fanotify.c

Answer 1

您不应该手动指向LOCAL_C_INCLUDES中的NDK头。这应该是自动添加，指向正确的版本。但是，这里没有实际使用变量APP_PLATFORM或TARGET_PLATFORM。

相反，在文件APP_PLATFORM := android-23中添加jni/Application.mk。这应该使它使用正确的平台头构建，适用于所有体系结构。

Answer 2

除了@mstorsjo的答案之外，您还可以在NDK r14和更新版本中使用统一报头。这是一种新的标头形式，它将始终是最新的，而不是每个API级别都有不同的标题集。

与增加APP_PLATFORM相比，这样做的优点是您的APP_PLAFORM不能高于您的minSdkVersion (参见我们的常见问题)。由于fanotify是在一个相当旧的内核版本(2.6.36用于fanotify_init)中引入的，所以即使在旧版本的libc中不存在函数，您仍然可以用syscall(__NR_fanotify_init)调用它。尽管如此，ENOSYS始终是一种可能性。

默认情况下，在r14中，仍然会得到标头的旧形式。新的“统一标题”有您要寻找的标头。如果要尝试统一头，请在APP_UNIFIED_HEADERS := true中设置Application.mk (其他构建系统的设置可以在上面的链接中找到)。

在r15 (即将发布的第一个测试版)中，默认值已更改为新的标头，禁用它们的选项已经更改(请参阅r15中的同一文档)。