Remove support for RNDR/RNDRRS for aarch64 #32248

pull laanwj wants to merge 1 commits into bitcoin:master from laanwj:2025-04-remove-arm64-rndr changing 1 files +0 −73

laanwj commented at 6:17 AM on April 11, 2025: member
This hardware feature is
- Rarely supported on SoCs (and broken on like half of the chips that support it in the first place) (#31817). It is not clear if, or how, the brokenness will be worked around in the kernel, but working around it in user space seems the wrong thing to do, this is not the place to maintain special workarounds for specific hardware (which despite that, was attempted in #31826, but had to be reverted in #31908 due to other problems).
- Apparently not compiled into the release binary anymore (https://github.com/bitcoin/bitcoin/issues/31817#issuecomment-2795885962). Did check this at the time, but a build system change must have caused this, and went undetected.
- Hard to test in CI (as well as manually), due to unavailability of hardware.
Better to remove it.

This reverts commit aee5404e02e203a256c1a97b629b9b107cc8bb07 from #26839.

Closes #31817.

Remove support for RNDR/RNDRRS for aarch64 on Linux

This hardware feature is

- rarely supported on SoCs (and broken on like half of the chips that support it in the first place) (#31817)
- apparently not compiled into the release binary (https://github.com/bitcoin/bitcoin/issues/31817#issuecomment-2795885962)
- hard to test in CI, due to unavailable of hardware

Better to remove it.

This reverts commit aee5404e02e203a256c1a97b629b9b107cc8bb07.

Closes #31817.

7749d929a0

laanwj added the label Linux/Unix on Apr 11, 2025
laanwj added the label Utils/log/libs on Apr 11, 2025
DrahtBot commented at 6:17 AM on April 11, 2025: contributor


The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.



Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/32248.



Reviews

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Type Reviewers

ACK sipa, davidgumberg, achow101, w0xlt

Concept ACK hugohn, theStack

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Conflicts

Reviewers, this pull request conflicts with the following ones:
- #29641 (scripted-diff: Use LogInfo over LogPrintf [WIP, NOMERGE, DRAFT] by maflcko)
If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.
laanwj added the label Needs backport (29.x) on Apr 11, 2025
laanwj renamed this:
~~Remove support for RNDR/RNDRRS for aarch64 on Linux~~
Remove support for RNDR/RNDRRS for aarch64
on Apr 11, 2025
hugohn commented at 7:10 AM on April 11, 2025: contributor

ACK
sipa commented at 11:47 AM on April 11, 2025: member

utACK 7749d929a0d9dfe71541a22e557ea41e01df28ce
theStack commented at 7:15 PM on April 15, 2025: contributor

Concept ACK
davidgumberg commented at 12:57 AM on April 16, 2025: contributor

utACK https://github.com/bitcoin/bitcoin/commit/7749d929a0d9dfe71541a22e557ea41e01df28ce

There are other sources of entropy in SeedStartup which is SeedHardwareSlow's only caller.

Without SeedHardwareFast() doing anything, the only remaining source of entropy in SeedFast is the timestamp, but this seems okay to me, since two of SeedFast's users, SeedSlow and SeedPeriodic, have other entropy sources.

The other place SeedFast() gets called is when ProcRand() is invoked with RNGLevel::Fast, the two places I see where that happens is in RandomInit()(only used by kernel and the wallet tool) and GetRandBytes(). GetRandBytes() is a little bit more all over the code base, but from what I can tell, nothing that uses it needs more entropy than the timestamp.
DrahtBot requested review from theStack on Apr 16, 2025
laanwj commented at 3:03 AM on April 16, 2025: member

but from what I can tell, nothing that uses it needs more entropy than the timestamp.

i wouldn't say this is the ideal situation, clearly adding hardware randomness when available (and safe to use) is preferable, it's just that it's not, here.
maflcko added the label DrahtBot Guix build requested on Apr 16, 2025
achow101 assigned achow101 on Apr 16, 2025
achow101 commented at 6:41 PM on April 16, 2025: member

ACK 7749d929a0d9dfe71541a22e557ea41e01df28ce
w0xlt commented at 6:54 PM on April 16, 2025: contributor

utACK https://github.com/bitcoin/bitcoin/pull/32248/commits/7749d929a0d9dfe71541a22e557ea41e01df28ce
achow101 merged this on Apr 16, 2025
achow101 closed this on Apr 16, 2025
maflcko removed the label DrahtBot Guix build requested on Apr 17, 2025
fanquake removed the label Needs backport (29.x) on Apr 17, 2025
fanquake commented at 10:55 AM on April 17, 2025: member

Backported in #32292.
fanquake referenced this in commit 1393ad4308 on Apr 17, 2025
sedited referenced this in commit a9c46ce3c3 on Apr 24, 2025
fanquake referenced this in commit ca70d5cb25 on May 6, 2025
fanquake referenced this in commit 589b56192f on May 22, 2025
stickies-v referenced this in commit 772a33e052 on May 23, 2025
luke-jr referenced this in commit ce1ac40fea on Jun 6, 2025
achow101 commented at 10:03 PM on June 17, 2025: member

Is there any interest in having this working? It appears that the Qualcomm Snapdragon X line of CPUs (currently available in both laptops and mini PCs) both have this capability, and also have the broken implementation. With WSL, I was able to verify that the reverted implementation did not work on Snapdragon X, and test the various fix PRs.
laanwj commented at 6:21 PM on June 18, 2025: member

Not sure. It's good that one of us can test it now. And i'm not opposed to re-adding support when it makes sense, but we still can't test it in CI. And still standing by that working around hardware issues in user-space is questionable, makes it seem it's just not taken seriously by the vendor.
yuvicc referenced this in commit 069643f094 on Jul 6, 2025
bug-castercv502 referenced this in commit 5b0af4b944 on Sep 28, 2025
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BigcoinBGC referenced this in commit 2be77ff3bd on Jun 30, 2026
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