libjpeg-turbo for Android: how to organize runtime selection of NEON / non-NEON code?

Question

I'm using a libjpeg-turbo port for Android. It's not much different from the base jpeg-turbo in terms of source code: http://git.linaro.org/gitweb?p=people/tomgall/libjpeg-turbo/libjpeg-turbo.git;a=shortlog;h=refs/heads/android

There is a module (static library) consisting of 2 cpu features-dependent files: jsimd_arm_neon.S and jsimd_arm.c. I want to compile jpeg-turbo with NEON support, I must define __ARM_HAVE_NEON and compile this module with -march=armv7-a -mfpu=neon. I want the library to run on older hardware with no Neon support (like Tegra 2), I should remove neon compiler flag and undef __ARM_HAVE_NEON.

My question is: how to compile it so that neon or non-neon path can be selected at runtime without SIGILL on non-neon hardware? I know how to check for NEON at runtime, but I don't know how to modify libjpeg-turbo and organize libraries.

Answer 1

An old question but I'll add to it anyway just in case. Someone did go into detail and one of the issues was dynamically selecting NEON. It is explained here: https://stackoverflow.com/a/20697814/712413.

The relevant section is item 4 to modify some lines in the init_simd() method.