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armhf NEON exception for chromium


The latest chromium is failing to build on armhf because upstream broke non-NEON builds. While that is technically an upstream bug, I'm not sure upstream is going to care enough to even accept a patch to fix it. I understand that the baseline for the armhf architecture is to not support NEON, but folks in #debian-arm suggested that I specifically ask for an exception for chromium.

At this point I'm pretty confident in assuming that folks running 13 year old arm  boards or newer rpi zero boards with 512MB of ram will not be using that hardware to browse the web with debian's chromium package. That leaves those using chromium for scripts or ci tests (eg, jquery-timepicker) on older armhf boards. The ci.debian.net infrastructure is newer than buildds, so I hopeful that they're mostly (or entirely?) machines that support NEON. And of course, chromium built with NEON support should be at least a small speed improvement for users running the browser on newer arm v7 hardware, although I lack the hardware to quantify that.

So my proposal for chromium is this:
a) Enable NEON for chromium's armhf build.
b) Add a check in debian/rules for 'neon' in /proc/cpuinfo's Features: line, and fail to build if NEON is not present. This should ensure that any buildds or downstream builders don't waste resources configuring/building chromium on a non-NEON board only to have it fail somewhere in the middle.
c) Using the current shell script wrapper for chromium (which already checks for things like SSE3 cpu instructions on x86), check for NEON support at startup by also looking for the string 'neon' in /proc/cpuinfo; if NEON is not supported, print an error message and exit before launching the chromium binary.
d) Ask the buildd admins to restrict building of chromium from any Armada XP buildds, which appear to be the only armhf buildds left in rotation that lack NEON support. If they are unwilling/unable to do this, then I'll have to play the giveback game for armhf (step right up! everyone's a winner!), which I often end up having to do currently because the 2-3 day armhf builds will sometimes hang/crash halfway through.

Any thoughts on this? Please explicitly Cc me on replies, as I'm not subscribed to any of the lists.


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