[Android] fseeko and ftello not supported on arm32 & x86 below API level 24 without disabling _FILE_OFFSET_BITS=64

[steveisok]

From https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md

Android does not require the _LARGEFILE_SOURCE macro to be used to make fseeko and ftello available. Instead they're always available from API level 24 where they were introduced, and never available before then.

An easy solution would be to bump the min API level to 24, but that is not solely a technical decision.

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[akoeplinger]

Where are these functions used? I can't seem to find any in the runtime.

[steveisok]

It starts here

runtime/src/native/corehost/hostmisc/pal.h

Line 9 in 21e92cb

#include <fstream>

I haven't looked deeply into if we'll be able to sidestep it somehow.

[akoeplinger]

you mean just including fstream causes these functions to be used somehow?

[steveisok]

Yeah, apparently. But we can't get rid of it because fstream types are used later on in the host PAL.

Here's an example of the build error you'll get:

In file included from /Users/steve/dev/customer-runtime/src/native/corehost/hostmisc/trace.cpp:4:
  In file included from /Users/steve/dev/customer-runtime/src/native/corehost/hostmisc/trace.h:7:
  In file included from /Users/steve/dev/customer-runtime/src/native/corehost/hostmisc/pal.h:9:
  /Users/steve/android-ndk-r27c/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/fstream:869:9: error: no member named 'fseeko' in the global namespace; did you mean 'fseek'?
    869 |   if (::fseeko(__file_, __width > 0 ? __width * __off : 0, __whence))
        |       ~~^
  /Users/steve/android-ndk-r27c/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/stdio.h:207:5: note: 'fseek' declared here
    207 | int fseek(FILE* _Nonnull __fp, long __offset, int __whence);
        |     ^

[jkoritzinsky]

These failures cause a lot of complications in our infrastructure today (see all checks around '$(TargetsLinuxBionic)' == 'true' and '$(TargetArchitecture)' == 'arm'.

We can likely skip defining _FILE_OFFSET_BITS=64 for android arm32, at least for the hosts layer. It's highly unlikely that someone would have a 4GB+ runtimeconfig.json or deps.json file for an Android arm32 app.

[vitek-karas]

We might be able to rewrite the host pal to not use fstream - the pal is pretty simple, so if we can find other ways to do it... the only limitation is that we don't want to make the host larger, so ideally use something which already exists in it.

[filipnavara]

We might be able to rewrite the host pal to not use fstream

That seems pretty doable: main...filipnavara:runtime:host-remove-fstream

I didn't update the test code but that only reads whole file into memory, essentially the same thing as done in json_parser.cpp, so I don't expect to be hard. I also didn't actually try to run it, so take it with a grain of salt, but it looks like a reasonable approach to take.