ARM NEON detection should use getauxval instead of parsing files in /proc

[James Cowgill]

It was suggested in this message from the Debian BTS that ffmpeg should use the getauxval function to detect the presence of NEON instead of parsing files in /proc. This is theoretically faster and doesn't require /proc to be mounted.

​https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=870676#49

[Aman]

somewhat related, I experienced SEGV on some android/arm devices when attempting to read /proc/self/auxv

OS Version: Android 9 (PS7242)
Report Version: 104

Exception Type: Unknown (SIGSEGV)

Application Specific Information:
Segfault

Thread 0 Crashed:
0   libc.so                         0xf23ac550          fread
1   libavutil.so                    0xd585c3ca          [inlined] get_hwcap (cpu.c:60)
2   libavutil.so                    0xd585c3ca          ff_get_cpu_flags_arm (cpu.c:109)

it appears since API20 getauxval() is part of android libc

​https://chromium.googlesource.com/skia/+/chrome/m49/platform_tools/android/third_party/cpufeatures/cpu-features.c#478

[Aman]

fixed in 2f299c0b8b4ab1b549b25ab48aa2adbc9f8718ea