[Sorry for the **long** delay in responding.] Andy Polyakov <ap...@openssl.org> wrote:
> > http://git.openssl.org/gitweb/?p=openssl.git;a=commitdiff;h=11208dcfb9105e8afa37233185decefd45e89e17 > made whole assembly pack Thumb2-friendly, so that now you should be able > to compile all modules. Please, double-check. This is awesome! I have a question about the `it` and `itt` instructions you inserted. You wrapped them in `#ifdef __thumb2__`, which is not wrong, but AFAICT is usually unnecessary. Is this to support some old assemblers that don't compile `it` (etc.) into nothing for non-Thumb builds? > There is no option to > disable NEON (yet?), because a) I want to expose it to more build cases > to catch eventual bugs; b) would like to suggest idea of supporting > Cortex-M with -march=armv6t2 -mthumb. Latter means that you'll loose > some performance, because it won't utilize word load instruction's > capability to handle misaligned access in ARMv7. But on the other hand > it won't have ideas about compiling NEON, and you'll be excused to think > about which particular Cortex-M is targeted, one will be able to cover > all with single config/buid. Can it be viable compromise? One would > still be able to tune for favorite Mx... For Cortex-M4 and friends, one would really want to use the full ARMv7-M instruction set (i.e. not compile for armv6t2). In general Cortex-M platforms are so limited that every bit of performance and space savings matters. So, I think it is definitely worthwhile to support the non-NEON ARMv7-M configuration. One easy way to do this would be to avoid building NEON code when __TARGET_PROFILE_M is defined. Alternatively, similar to what BoringSSL did, you could have an option that says "instead of doing runtime feature detection, instead detect features at compile time based on __ARM_NEON__ and the like." I think such a configuration would also help the C compiler do whole-program optimization better. Again, thanks for doing this! Cheers, Brian -- https://briansmith.org/
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