NDK: Unified Headers issue

[nurupo]

Description

Android NDK's unified headers cause compile errors in OpenSSL and TokTok C-Toxcore libraries. This doesn't happen with the deprecated headers.

OpenSSL:

./libcrypto.so: error: undefined reference to 'stderr'
./libcrypto.so: error: undefined reference to 'stdin'
./libcrypto.so: error: undefined reference to 'signal'
./libcrypto.so: error: undefined reference to 'tcsetattr'
./libcrypto.so: error: undefined reference to 'tcgetattr'

TokTok C-Toxcore:

../testing/DHT_test.c:208: error: undefined reference to 'stdin'
../toxcore/DHT.c:2404: error: undefined reference to 'rand'
../toxcore/DHT.c:1626: error: undefined reference to 'rand'
../toxcore/DHT.c:1629: error: undefined reference to 'rand'
../toxcore/DHT.c:1938: error: undefined reference to 'rand'
../toxcore/network.c:548: error: undefined reference to 'srand'

Environment Details

Not all of these will be relevant to every bug, but please provide as much
information as you can.

• NDK Version: 15.1.4119039
• Build system: standalone toolchain
• Host OS: Debian Jessie amd64
• Compiler: Clang? (whatever make_standalone_toolchain.py produces)
• ABI: arm
• STL: Not specified
• NDK API level: No idea
• Device API level: 14

[nurupo]

As far as Toxcore goes:

1. rand() is defined in C's stdlib.h.
2. You can see that network.h has an unconditional #include <stdlib.h>.
3. You can see that DHT.c, the one that we get error: undefined reference to 'rand' in, has an unconditional #include "network.h".
4. Thus DHT.c should have rand defined, as it includes network.h which includes stdlib.h.

The only way this error is possible is if rand is no defined in Unified Header's stdlib.h.

[enh]

how did you configure your standalone toolchain? looks like you've told the compiler to aim for a recent API level (where these symbols are available) but the linker to aim for an older one (where they were inline references to other symbols).

[nurupo]

I build it using multiple toolchains, each targeting different architectures. It fails for all toolchains I try, while it succeeds with --deprecated-headers flag when creating a toolchain and with older NDK versions.

I create a toolchain like this

export ANDROID_NDK_HOME=/opt/android-ndk
"$ANDROID_NDK_HOME/build/tools/make_standalone_toolchain.py" --arch $ARCH --api $API --install-dir "$TOOLCHAIN_DIR" --force

$API and $ARCH are 14 for arm, 21 for arm64, 21 for x86_64 and 14 for x86. Then I build using the corresponding toolchain, which are

arm-linux-androideabi
aarch64-linux-android
x86_64-linux-android
i686-linux-android

[nurupo]

Here is a build log, if it's of any help.

[nurupo]

Ok, specifying CFLAGS=-D__ANDROID_API__=$API fixed this for me

Didn't notice this before

Standalone toolchains using GCC are not supported out of the box. To use GCC, pass -D__ANDROID_API__=$API when compiling. Note: this is not something we will be fixing.

Using clang instead of gcc also works, e.g. for autotools-based projects CC=arm-linux-androideabi-clang CXX=arm-linux-androideabi-clang++ ./configure --host=arm-linux-androideabi ... works without disabling unified headers and without specifying __ANDROID_API__. I guess we are supposed to use clang anyway, given how gcc is deprecated since r12 or something like that.

[DanAlbert]

CC=arm-linux-androideabi-clang

FYI, CC=clang should work too. The triple prefix is unnecessary for Clang with standalone toolchains.

[dkhanchopoulo]

guys, please clarify how did you make it work with clang because
when I made a tool-chain with script https://github.com/supertuxkart/stk-code/blob/master/android/make.sh
it still has the issue for clang: clang50: error: unknown argument: '-mandroid'

[drFabio]

@nurupo Can you exemplify how you built it with ndk 15b?

[nurupo]

If I remember it right, using clang toolchain just worked for me. gcc on the other hand had issues and you had to specify CFLAGS=-D__ANDROID_API__= for it to work. You shouldn't be using gcc on Android anyway though, since its support on Android is being deprecated in favor of clang.

[drFabio]

THe CFLAGS was needed but I could got it only with a standalone toolchain not the installed NDK by android studio, will try from the scratch later and try with clang

[nurupo]

Standalone toolchains is what I'm using.

[drFabio]

That's probably why I was confused and the things were not working I was following the wiki with NDK root being the installed NDK.

Glad to know I'm not diverging the path.

Thanks a lot for your response @nurupo