Messages in this thread | | | Date | Mon, 7 Mar 2022 16:48:51 +0000 | Subject | Re: [PATCH RFC] arm64: improve display about CPU architecture in cpuinfo | From | Robin Murphy <> |
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On 07/03/2022 12:23 pm, Marc Zyngier wrote: > On Mon, 07 Mar 2022 12:13:50 +0000, > Rongwei Wang <rongwei.wang@linux.alibaba.com> wrote: >> >> >> >> On 3/7/22 4:45 PM, Marc Zyngier wrote: >>> On Mon, 07 Mar 2022 03:04:17 +0000, >>> Rongwei Wang <rongwei.wang@linux.alibaba.com> wrote: >>>> >>>> Now, it is unsuitable for both ARMv8 and ARMv9 to show a >>>> fixed string "CPU architecture: 8" in /proc/cpuinfo. >>> >>> Please read the various threads that have been going on over the past >>> 10+ years about *why* we don't allow this sort of change (TL;DR: it >>> breaks userspace, and we don't do that). >>> >>> Also, there is no material difference between v8 and v9 that would be >>> observable from userspace outside of the "Features:" line. And if that >>> doesn't convince you, just think of '8' as the number of bytes >>> used by > >> I got your point. It seems that we can regard '8' as the number of >> bytes. But what make me do this is that 'CPU architecture: 8' is >> confusing, especially those responsible for testing. >> And I believe that most people regard this '8' as ARMv8, maybe not. > > That was the original intention. But given that there is no userspace > visible difference between v8, v9 and whatever comes after it, this > is a pointless change. My comment about the size of a VA was just a > joke, and not something to be taken seriously. > >> In fact, I'm not sure it has potential ABI implications, so seek your >> advice. > > Plenty of userspace programs parse /proc/cpuinfo. If you replace '8' > with anything else, they will fail. Which is why although your patch > makes sense, it comes 10 years too late, and we can't change this > anymore.
And arguably it's not even too late, because 10 years ago this *did* say "AArch64". I don't remember all the exact details behind commit 44b82b7700d0 ("arm64: Fix up /proc/cpuinfo") - this just tickled enough of a memory to go and look up the git history - but I don't think we changed any of those fields without a real reason.
Robin.
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