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Message #148275
[Bug 1520627] Re: New personality for more accurate armv7l emulation on arm64
It looks like we could off you a kernel command line like
compat_uts_machine=<string> to allow the 32bit architecture be
overridden at boot time for the life of the machine.
** Changed in: linux (Ubuntu)
Status: Confirmed => In Progress
** Changed in: linux (Ubuntu)
Importance: Undecided => High
** Changed in: linux (Ubuntu)
Assignee: (unassigned) => Andy Whitcroft (apw)
** Also affects: linux (Ubuntu Xenial)
Importance: High
Assignee: Andy Whitcroft (apw)
Status: In Progress
** Also affects: linux (Ubuntu Wily)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Wily)
Status: New => In Progress
** Changed in: linux (Ubuntu Wily)
Importance: Undecided => Medium
** Changed in: linux (Ubuntu Wily)
Assignee: (unassigned) => Andy Whitcroft (apw)
** Changed in: linux (Ubuntu Xenial)
Milestone: None => ubuntu-15.12
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https://bugs.launchpad.net/bugs/1520627
Title:
New personality for more accurate armv7l emulation on arm64
Status in linux package in Ubuntu:
In Progress
Status in linux source package in Wily:
In Progress
Status in linux source package in Xenial:
In Progress
Bug description:
We're working on bringing up new arm64 builder infrastructure in
Launchpad scalingstack to replace the current bare-metal builders, and
the current plan is that they should be able to cover armhf as well.
Ideally, we would be able to do this using the same guest images:
scalingstack builders are reset at the end of the previous build so
that latency for new builds is lower when the build farm isn't at 100%
use, which means that we don't in general know which architecture a
given builder is going to need to build next, so we can get better
density out of our hardware by having the same guest images be able to
handle more than one architecture.
Things mostly work just by chrooting into an armhf chroot under
linux32. However, this causes "uname -m" to print "armv8l", while our
current value on our armhf builders is "armv7l". I'd initially
thought that this would be tolerable, but my understanding from Adam
Conrad is that the breakage from poorly-written build scripts that
misdetect the architecture as a result is quite widespread. So, we
would like to have a personality value available that would cause
"uname -m" to print "armv7l".
This doesn't look completely trivial, because newuname() basically
just has compat and non-compat mode for architectures based on whether
the personality is PER_LINUX32 or not, and doesn't currently seem to
have extension points beyond that. I'm hoping this is fixable. If
not, we need to know with as much lead time as possible so that we can
bring up separate armhf guests, since that's going to be a fair amount
of work for us to arrange.
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References