Android-NDK: Run time errors when using shmget, shmctl, shmdt in Android API 27

Issue

I need to port a native library which uses System V shared memory for IPC. There are calls to methods like shmget(), shmctl() & shmdt(). I was able to compile the native code and build the native library, but when I run the library with the help of emulator, the application is crashing.

Below is the line where it's crashing.

iShmId = shmget( tKey, iSize, IPC_CREAT | IPC_EXCL | _DEF_ACCESS );

I'm using Android Studio, Android API level 27.

I came across this link: How to use shared memory in android native code? where it's said that these API's are not supported, but I thought that the latest Android API level 27 might have support for the same.

I verified the ndk-bundle\sysroot\usr\include\sys\shm.h header and these API's are seem to be supported since API 26, below is the extract from shm.h file.

#if __ANDROID_API__ >= 26
void* shmat(int __shm_id, const void* __addr, int __flags) __INTRODUCED_IN(26);
int shmctl(int __shm_id, int __cmd, struct shmid_ds* __buf) __INTRODUCED_IN(26);
int shmdt(const void* __addr) __INTRODUCED_IN(26);
int shmget(key_t __key, size_t __size, int __flags) __INTRODUCED_IN(26);

#endif /* __ANDROID_API__ >= 26 */

Can anyone please let me know what am I missing here. As I'm able to compile & build the library, these API's should be supported. So, I should be missing something.

Below is the error from Logcat:

2018-12-09 12:43:51.313 31453-31473/com.android.phone A/libc: Fatal signal 6 (SIGABRT), code -6 (SI_TKILL) in tid 31473 (HwBinder:31453_), pid 31453 (m.android.phone)
2018-12-09 12:43:51.490 31529-31529/? A/DEBUG: backtrace:
2018-12-09 12:43:51.490 31529-31529/? A/DEBUG:     #00 pc 00000b39  [vdso:e9577000] (__kernel_vsyscall+9)
2018-12-09 12:43:51.490 31529-31529/? A/DEBUG:     #01 pc 0001fdf8  /system/lib/libc.so (syscall+40)
2018-12-09 12:43:51.490 31529-31529/? A/DEBUG:     #02 pc 000321fe  /system/lib/libc.so (shmget+46)
2018-12-09 12:43:51.491 31529-31529/? A/DEBUG:     #03 pc 00016b57  /data/app/com.example.****.app--7DjBy2wqavG-QlF-n6rDg==/lib/x86/libNativeLib.so
2018-12-09 12:43:51.491 31529-31529/? A/DEBUG:     #04 pc 0001684f  /data/app/com.example.****.app--7DjBy2wqavG-QlF-n6rDg==/lib/x86/libNativeLib.so (GetShmSegment+447)
2018-12-09 12:43:51.491 31529-31529/? A/DEBUG:     #05 pc 00014940  /data/app/com.example.****.app--7DjBy2wqavG-QlF-n6rDg==/lib/x86/libNativeLib.so
2018-12-09 12:43:51.491 31529-31529/? A/DEBUG:     #06 pc 000148e7  /data/app/com.example.****.app--7DjBy2wqavG-QlF-n6rDg==/lib/x86/libNativeLib.so (GetCurrentProcessId+23)
2018-12-09 12:43:51.491 31529-31529/? A/DEBUG:     #07 pc 0001b7cf  /data/app/com.example.****.app--7DjBy2wqavG-QlF-n6rDg==/lib/x86/libNativeLib.so (_init+207)
2018-12-09 12:43:51.491 31529-31529/? A/DEBUG:     #08 pc 00023d68  /system/bin/linker (__dl__ZN6soinfo17call_constructorsEv+696)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #09 pc 00023b6a  /system/bin/linker (__dl__ZN6soinfo17call_constructorsEv+186)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #10 pc 0000c156  /system/bin/linker (__dl__Z9do_dlopenPKciPK17android_dlextinfoPKv+2102)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #11 pc 00007263  /system/bin/linker (__loader_android_dlopen_ext+83)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #12 pc 00000eb6  /system/lib/libdl.so (android_dlopen_ext+38)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #13 pc 00003998  /system/lib/libnativeloader.so (android::OpenNativeLibrary(_JNIEnv*, int, char const*, _jobject*, _jstring*, bool*, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>*)+424)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #14 pc 0031eb61  /system/lib/libart.so (art::JavaVMExt::LoadNativeLibrary(_JNIEnv*, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&, _jobject*, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>*)+3009)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #15 pc 000036f6  /system/lib/libopenjdkjvm.so (JVM_NativeLoad+454)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #16 pc 00022d06  /system/lib/libopenjdk.so (Runtime_nativeLoad+38)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #17 pc 001149ba  /system/framework/x86/boot.oat (offset 0x114000) (java.lang.Runtime.nativeLoad [DEDUPED]+202)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #18 pc 005f0d52  /system/lib/libart.so (art_quick_invoke_static_stub+418)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #19 pc 000a30df  /system/lib/libart.so (art::ArtMethod::Invoke(art::Thread*, unsigned int*, unsigned int, art::JValue*, char const*)+239)
2018-12-09 12:43:51.492 31529-31529/? A/DEBUG:     #20 pc 0029bca2  /system/lib/libart.so (art::interpreter::ArtInterpreterToCompiledCodeBridge(art::Thread*, art::ArtMethod*, art::ShadowFrame*, unsigned short, art::JValue*)+338)

Solution

The syscall wrappers being available in libc is not the same as the kernel making those syscalls available. It would seem that those syscalls are not allowed, as they are not mentioned in SYSCALLS.TXT or SECCOMP_WHITELIST_*.TXT.

https://android.googlesource.com/platform/bionic/+/master/libc

Did you check for errors from your syscalls? Presumably the first one failed with ENOSYS.

EDIT:

If you look at the most recent copy of this header the comments explain this: https://android.googlesource.com/platform/bionic/+/master/libc/include/sys/shm.h. Those haven't made it into a released NDK yet though.

Answered By - Dan Albert