Link time optimization and x86-64-v2 - old CPU's losing support.

30 July 2021, 23:24:39

https://www.phoronix.com/scan.php?page=news_item&px=Arch-Linux-LTO-Proposed
Older ie roughly pre 2008 CPU's may no longer function after x86-64-v2 is adopted. Kind of like dropping 32 bit support but for older 64 bit machines. Useful to know about, to make plans if you have one of these.
I was reading some comments on the Yay AUR page about LTO which is how I came across this, some packages including Yay don't build with LTO. It might soon be the default as several other distros are using it, to make smaller faster binaries.

Re: Link time optimization and x86-64-v2 - old CPU's losing support.

Reply #1 – 31 July 2021, 05:07:14

But that info is sort of outdated, what they now intend to do is create an entirely new set of x86_64-v3 repo packages alongside the basic x86_64 ones, the same way there used to be 32 bit and 64 bit versions:
"Provide a x86-64-v3 microarchitecture level port"
https://gitlab.archlinux.org/archlinux/rfcs/-/commit/b039e0ddeeed0f08bf4df510ea78a6c884439eeb
Which is kind of handy as I just found my late C2D 2009-2011 mobile CPU is only V1 when I checked

Code: [Select]

$ /lib/ld-linux-x86-64.so.2 --help
Subdirectories of glibc-hwcaps directories, in priority order:
  x86-64-v4
  x86-64-v3
  x86-64-v2
(none of those say supported next to them)

So it should be a fair while yet before the old x86_64 gets discontinued, although splitting it off you can guess where it's eventually headed.
The lto thing might take a bit more memory and build time for packages.