Bug#751856: libav FTBFS on arm64

[peter green]

Package: libav
Version: 6:10.1-1
Severity: important


I've been trying to build libav for arm64 (in a user mode qemu chroot),
I removed  opencv, frei0r and x264 from build-depends to break the look
(as suggested in README.source)

gcc -I. -I/libav-10.1 -D_FORTIFY_SOURCE=2 -D_ISOC99_SOURCE
-D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_POSIX_C_SOURCE=200112
-D_XOPEN_SOURCE=600 -DPIC -fPIC -g -MMD -MF
libavcodec/aarch64/h264cmc_neon.d -MT libavcodec/aarch64/h264cmc_neon.o
-c -o libavcodec/aarch64/h264cmc_neon.o
/libav-10.1/libavcodec/aarch64/h264cmc_neon.S
/libav-10.1/libavcodec/aarch64/h264cmc_neon.S: Assembler messages:
/libav-10.1/libavcodec/aarch64/h264cmc_neon.S:391: Error: bad expression
at operand 2 -- `adrp x6,#:pg_hi21:rv40bias'
/libav-10.1/libavcodec/aarch64/h264cmc_neon.S:392: Error: bad expression
at operand 2 -- `adrp x6,#:pg_hi21:rv40bias'
/libav-10.1/libavcodec/aarch64/h264cmc_neon.S:393: Error: bad expression
at operand 2 -- `adrp x6,#:pg_hi21:rv40bias'
/libav-10.1/libavcodec/aarch64/h264cmc_neon.S:394: Error: bad expression
at operand 2 -- `adrp x6,#:pg_hi21:rv40bias'
/libav-10.1/Makefile:47: recipe for target
'libavcodec/aarch64/h264cmc_neon.o' failed
make[1]: *** [libavcodec/aarch64/h264cmc_neon.o] Error 1
make[1]: Leaving directory '/libav-10.1/debian-shared'
debian/rules:81: recipe for target 'build-stamp-shared' failed
make: *** [build-stamp-shared] Error 2

The block of code in question looks like

#if CONFIG_RV40_DECODER
const   rv40bias
        .short           0, 16, 32, 16
        .short          32, 28, 32, 28
        .short           0, 32, 16, 32
        .short          32, 28, 32, 28
endconst

        h264_chroma_mc8 put, rv40
        h264_chroma_mc8 avg, rv40
        h264_chroma_mc4 put, rv40
        h264_chroma_mc4 avg, rv40
#endif

I had a look though the ubuntu patches but didn't find anything that
looked immediately relavent. I'm now attempting to disable NEON to see
if that makes the package build.