NDK 15 breaks mmap on Nexus 5

[greenrobot]

Description

Using NDK 15.1.4119039 we are seeing a weird runtime failure in our app and tests on certain devices. We tracked it done to this source line:

r = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);

On a Nexus 5 running Android 6.0.1, this will fail (MAP_FAILED returned) with errno == EINVAL. With earlier NDKs this was never a problem. Also, when running on a Nexus 5x, it is not a problem when building with NDK15.

Environment Details

• NDK Version: 15.1.4119039
• Build sytem: cmake
• Host OS: Windows
• Compiler: Clang ("-DANDROID_TOOLCHAIN=clang" passed via gradle externalNativeBuild.cmake.arguments)
• ABI: "armeabi-v7a" (others built are "arm64-v8a" and "x86")
• STL: "-DANDROID_STL=c++_static"
• NDK API level: 25
• Device API level: 23

[enh]

are you building with _FILE_OFFSET_BITS=64 by any chance?

[greenrobot]

@enh Yes

[enh]

yeah, that should be fixed by https://android-review.googlesource.com/429481/. in the meantime, not building with _FILE_OFFSET_BITS=64 is a workaround.

[greenrobot]

Thanks. I'll just stick to NDK14b until the next NDK release.

[DanAlbert]

Just don't set _FILE_OFFSET_BITS=64 for pre-L targets. The difference between r14 and r15 here is that doing that used to be a no-op. Even when we do fix this, your code still won't build if you're setting that for 32-bit code because there wasn't an mmap64 for your target API level.

[DanAlbert]

Oh, actually:

NDK API level: 25
Device API level: 23

Don't do that. NDK API level is the minimum version your app supports.

That said, mmap64 was in 21 and you're targeting 25, so this shouldn't be a problem... @enh is taking a closer look.

[enh]

yeah, seems like we're still missing something here. is this literally the code? offset is 0?

r = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);

i don't suppose you know how to run strace to see what's really going on? if not, do you have a small reproduceable test case?

[greenrobot]

Actually, my gradle setup is:

    minSdkVersion 10
    targetSdkVersion 25

and yes, that's literally the code. Haven't used strace yet.

[DanAlbert]

For the NDK your target API is actually your minSdkVersion (just confirmed that with one of our gradle people). With r15 if you set it something lower than we support (like 10), we'll bump you up to the minimum (14), so your actual NDK API level should be 14.

In that case, you are hitting the case of the other bug. You'll need to make sure you're not passing -D_FILE_OFFSET_BITS=64 for targets that old and then everything should work fine.