issue #470 - working 32-bit ARM

[clach04]

No description provided.

[clach04]

Fixes Illegal instruction at runtime.

NOTE not tested on Raspberry. Only on Armbian with OdroixXU4.

Tested with neon fpu flag. Also had success with:

• -mfpu=neon-fp16
• -mfpu=neon-vfpv3

[ggerganov]

We need a way to detect 32-bit ARM in the Makefile and choose the respective flags

[clach04]

We need a way to detect 32-bit ARM in the Makefile and choose the respective flags

That's what this PR does, the original code did not do this. Can you clarify in case I'm missing something?

[ggerganov]

My Raspberry Pi 4 reports armv7l, but I can use -mfpu=neon-fp-armv8 successfully.
It has much better performance compared to the proposed -mfpu=neon.

Does -mfpu=neon-fp-armv8 not work for you?

[clach04]

My Raspberry Pi 4 reports armv7l, but I can use -mfpu=neon-fp-armv8 successfully. It has much better performance compared to the proposed -mfpu=neon.

Ahhh, sounds like you have a 64-bit board but a 32-bit Operating System? Can you confirm?

Does -mfpu=neon-fp-armv8 not work for you?

No it does not, I do NOT have a 64-bit Pi 4, I have an armv7 board with no v8 extensions (see https://forums.raspberrypi.com/viewtopic.php?t=282791 for Pi4 self reporting, it reports as v7 in a 32-bit OS but allows access to v8 instructions). My board is ONLY 32-bit.

New idea/proposal (assuming you have a really have pi4 board with 32-bit OS), in the 32-bit OS (v7) code block we add an additional conditional for detecting a raspberry pi board? Thoughts?

Slightly off topic, you might find moving to a 64-bit OS gains you some extra performance else where for your board, then the makefile would drop into the next "if" check.

[ggerganov]

Yes, it looks like I am using a 32-bit OS on my 64-bit RPi4. Thanks for clearing this up.
It would be very useful to have a branch in the Makefile for my use case, since I don't see mysql upgrading the OS anytime soon. But if there is no clean way to do it, we can merge it like this and I will simply modify the Makefile locally when working on my RPi4

[clach04]

What do you get for:

cat /proc/cpuinfo |grep 'model name'

(| head -1) ?

If you get ARMv7 Processor rev 4 (v7l) (4 or above) that might be the (slightly messy) heuristic that could work 🤞 .

I don't have a Pi4 to check with 😿 This might also work for Pi 3b+ boards too.

[ggerganov]

$ cat /proc/cpuinfo |grep 'model name'
model name	: ARMv7 Processor rev 3 (v7l)

[clach04]

Hmmm, that completely surprised me. Sadly, I think your idea of a private change is the safest :-( I was really hoping we could automate this nicely.

Alternative idea, mention pi 4 can use v8 extensions in a comment (e.g. the ones that worked for you) so its documented as a potential option?