_FILE_OFFSET_BITS=64 breaks compilation with Android NDK r15 and API<24

[d.mikhirev@…]

Behavior of _FILE_OFFSET_BITS in Android NDK is described at android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md

Android support for _FILE_OFFSET_BITS=64 (which turns off_t into off64_t and replaces each off_t function with its off64_t counterpart, such as lseek in the source becoming lseek64 at runtime) was added late. Even when it became available for the platform, it wasn‘t available from the NDK until r15. Before NDK r15, _FILE_OFFSET_BITS=64 silently did nothing: all code compiled with that was actually using a 32-bit off_t. With a new enough NDK, the situation becomes complicated. If you’re targeting an API before 21, almost all functions that take an off_t become unavailable. You‘ve asked for their 64-bit equivalents, and none of them (except lseek/lseek64) exist. As you increase your target API level, you’ll have more and more of the functions available. API 12 adds some of the <unistd.h> functions, API 21 adds mmap, and by API 24 you have everything including <stdio.h>.

In filesystem/src/operations.cpp _FILE_OFFSET_BITS is unconditionally defined to 64 in hope that

at worst, these defines may have no effect

It actually breaks compilation with Android NDK r15 if __ANDROID_API__ is less than 24.

[joerg@…]

It is also breaks compilation with Android NDK 16.0.4442984 and API level lower then 21. With API Level 21 it compiles without any error. See also my github report ​https://github.com/boostorg/filesystem/issues/65

[rowanj@…]

Also affected by this issue and can verify that the patch on GitHub resolved it

[anonymous]

Where is the patch that fixes this? I'm running into this same issue using LLVM STL with Clang on NDK r16b while building boost 1.64. This is blocking my transition away from GNU STL. Note that GNU STL is deprecated and NDK team will be removing it soon. I feel a sense of urgency because of that.

[joerg@…]

This ​android-boost-1_65_1-patches.patch in my github report ​https://github.com/boostorg/filesystem/issues/65. For the information, this patch only fix the build issue and not the problem! It builds and it also "runs" but it could be a problem on "large filesystem/files" ... I'm not sure. I'm not a filesystem expert. I still waiting for any boost filesystem contributor.

[anonymous]

it could be a problem on "large filesystem/files" ... I'm not sure

to be clear: if your code worked on an older NDK, your patch is correct: it restores the old "use a 32-bit off_t" behavior. it's a neutral "(in)correctness preserving" change :-)

[anonymous]

The issue is still not fixed. The issue is quite serious: Boost.Filesystem does not compile on Android. It is not the same issue as #13274.

There is a pull request, addressing the issue: ​https://github.com/boostorg/filesystem/pull/69