Discussion:
armhf: neon instruction ?
(too old to reply)
Lennart Sorensen
2022-01-10 15:10:01 UTC
Permalink
Dear arm porters,
-march=armv7-a -mfpu=neon-vfpv4 -mfloat-abi=hard -mfp16-format=ieee
* https://salsa.debian.org/debian-phototools-team/highway/-/blob/master/CMakeLists.txt#L182-185
Well the debian armhf specification does NOT require neon support,
so packages should not require neon unless it is optional and provided
as runtime detected code or an alternate library to load or whatever
method works.
--
Len Sorensen
Arnd Bergmann
2022-01-10 15:20:01 UTC
Permalink
Dear arm porters,
-march=armv7-a -mfpu=neon-vfpv4 -mfloat-abi=hard -mfp16-format=ieee
* https://salsa.debian.org/debian-phototools-team/highway/-/blob/master/CMakeLists.txt#L182-185
A package built with those options is likely to not work on currently supported
processors that only have VFPv3 rather than VFPv4 (All Cortex-A8, A9 and more).
The highest supported FPU implemetnation at the moment is "vfpv3-d16", so
no VFPv4 extensions, NEON or extra double-precision registers, see also [1].

A future Debian release might drop support for implementations with less than 32
double-precision registers or with no NEON, but would likely still need runtime
detection for vfpv4 features that are not in vfpv3 (fused
multiply-accumulate and
half precision floats).

Arnd

[1] https://wiki.debian.org/ArmHardFloatPort/VfpComparison
Mathieu Malaterre
2022-01-10 15:40:01 UTC
Permalink
Hi Lennart !

On Mon, Jan 10, 2022 at 4:21 PM Lennart Sorensen
Post by Lennart Sorensen
Dear arm porters,
-march=armv7-a -mfpu=neon-vfpv4 -mfloat-abi=hard -mfp16-format=ieee
* https://salsa.debian.org/debian-phototools-team/highway/-/blob/master/CMakeLists.txt#L182-185
Well the debian armhf specification does NOT require neon support,
so packages should not require neon unless it is optional and provided
as runtime detected code or an alternate library to load or whatever
method works.
Please check:

https://packages.qa.debian.org/f/fftw3.html

Search for `-mfpu=neon` at:

* https://buildd.debian.org/status/fetch.php?pkg=fftw3&arch=armhf&ver=3.3.8-2&stamp=1536684083&raw=0

I believe my issue (as explained by Arnd) is indeed the vfpv4 features.
Loading...