[BUG] libz.a for armeabi-v7a is missing symbols

[topjohnwu]

Using NDK r22-beta1 (22.0.6917172-beta1) on macOS with ndk-build to build static binaries.
When statically linking libz.a in 32 bit ARM code, the linker will complain with the following error:

ld: error: undefined symbol: arm_cpu_enable_crc32
>>> referenced by deflate.c:0 (external/zlib/deflate.c:0)
>>>               deflate.o:(deflateInit2_) in archive /Volumes/Developer/android/sdk/ndk/magisk/toolchains/llvm/prebuilt/darwin-x86_64/bin/../sysroot/usr/lib/arm-linux-androideabi/21/libz.a

ld: error: undefined symbol: x86_cpu_enable_simd
>>> referenced by deflate.c:0 (external/zlib/deflate.c:0)
>>>               deflate.o:(deflateInit2_) in archive /Volumes/Developer/android/sdk/ndk/magisk/toolchains/llvm/prebuilt/darwin-x86_64/bin/../sysroot/usr/lib/arm-linux-androideabi/21/libz.a
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

Using readelf to print out symbols of all libz.a for arm 32, it seems all libz.a archives are missing cpu_features.o, causing the following symbols to be undefined:

int arm_cpu_enable_crc32;
int arm_cpu_enable_pmull;
int x86_cpu_enable_sse2;
int x86_cpu_enable_ssse3;
int x86_cpu_enable_simd;

This issue does not happen on any other arch.

[enh-google]

hmm. i wrote this in the Android.bp:

    // This file doesn't build for non-neon, so it can't be in the main srcs.
    "cpu_features.c",

i've just done an upstream update anyway so i'll have a look and see if that's actually/still true. (things might get a bit interesting if non-neon is just not supported, but we can always hack in some stubs.)

works for me locally, but iirc i need to let treehugger actually do an NDK build to hit the non-neon case anyway: https://android-review.googlesource.com/c/platform/external/zlib/+/1519998

[enh-google]

okay, the obvious "let's just build it" failed:

external/zlib/cpu_features.c:56:13: error: function '_cpu_check_features' has internal linkage but is not defined [-Werror,-Wundefined-internal]
static void _cpu_check_features(void);
            ^
external/zlib/cpu_features.c:70:42: note: used here
    pthread_once(&cpu_check_inited_once, _cpu_check_features);
                                         ^
1 error generated.

...but playing with the CPU_NO_SIMD #define seems to work. i've uploaded a new patchset to the same CL.

[hhb]

Prebuilt updated in
https://android-review.googlesource.com/c/platform/prebuilts/ndk/+/1564881