[opus] Cross-compiling Opus for Android arm64

[Kostya Vasilyev]

Hello,

I'm trying to compile Opus for Android arm64 (and ultimately other arch's)
using the CMakeLists.txt file available in the repository.

My cmake commands are like this:

https://gist.github.com/kvasilye/9004332a5f3f90f2a6e868090d004d7b

This produces an error:

ld: error: undefined symbol: celt_pitch_xcorr_neon
>>> referenced by pitch.c:347 (/home/
ANT.AMAZON.COM/kvasilye/opus/celt/pitch.c:347)
>>>               CMakeFiles/opus.dir/celt/pitch.c.o:(pitch_search)
>>> referenced by celt_lpc.c:314 (/home/
ANT.AMAZON.COM/kvasilye/opus/celt/celt_lpc.c:314)
>>>               CMakeFiles/opus.dir/celt/celt_lpc.c.o:(_celt_autocorr)
>>> referenced by burg_modified_FIX.c:98 (/home/
ANT.AMAZON.COM/kvasilye/opus/silk/fixed/burg_modified_FIX.c:98)
>>>
CMakeFiles/opus.dir/silk/fixed/burg_modified_FIX.c.o:(silk_burg_modified_c)
>>> referenced 2 more times

Next, I tried to write my own CMakeLists.txt and got stuck too - the
undefined symbol above is defined in celt_pitch_xcorr_arm.s which as I
understand uses ARM assembler syntax.

I converted the file to GNU syntax using the provided Perl script.

Trying to compile the output with aarch64-linux-gnu-as gives a whole bunch
of errors like:

third_party/cmake-build-opus-android-arm64-v8a-Debug/celt_pitch_xcorr_arm_gnu.S:
Assembler messages:
third_party/cmake-build-opus-android-arm64-v8a-Debug/celt_pitch_xcorr_arm_gnu.S:1:
Error: unknown pseudo-op: `.syntax'
third_party/cmake-build-opus-android-arm64-v8a-Debug/celt_pitch_xcorr_arm_gnu.S:2:
Error: junk at end of line, first unrecognized character is `@'
third_party/cmake-build-opus-android-arm64-v8a-Debug/celt_pitch_xcorr_arm_gnu.S:3:
Error: junk at end of line, first unrecognized character is `@'
third_party/cmake-build-opus-android-arm64-v8a-Debug/celt_pitch_xcorr_arm_gnu.S:4:
Error: junk at end of line, first unrecognized character is `@'
third_party/cmake-build-opus-android-arm64-v8a-Debug/celt_pitch_xcorr_arm_gnu.S:5:
Error: junk at end of line, first unrecognized character is `@'

So it looks unhappy with the syntax.

Questions:

1 - What is the right way to compile Opus for Android on arm64-v8a?

2 - If I wanted to compile the asm file, how can I do that?

3 - Is this asm file for both armeabi-v7a and arm64-v8a or just
for armeabi-v7a? The symbol is required for arm64-v8a, but there is a
directive ".arch armv7-a" at the top of the file so I'm confused.

I really don't know anything about arm assembly to figure these out on my
own, any help would be appreciated!

Thanks,
-- K
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