Comment by Polizeiposaune
14 hours ago
Details of the errata from a comment in the diff:
"Write both dist bytes as a single 2-byte store. This avoids the `movb %ch, [mem]` instruction pattern (store from high-byte register alias) that LLVM otherwise emits when dist arrives as a wide register. That pattern triggers the Intel Raptor Lake CPU errata, causing silent 2-byte stores that corrupt the adjacent `len` byte."
How did this get past validation at Intel?
This is worse than https://en.wikipedia.org/wiki/Pentium_FDIV_bug
There's another blog post going into more depth about the issue here: https://fgiesen.wordpress.com/2025/05/21/oodle-2-9-14-and-in... where they speculate that it seems to relate to both other clock-related instability on specific Raptor Lake parts and possibly the overarching voltage control problems that the platform had early on; I can't tell entirely from the bug reports whether the behavior reliably reproduces on 100% of Raptor Lakes but the indicators I'm reading point to that it doesn't. It is concerning that Intel didn't get back to Mozilla about it though, since it's certainly a lot more than a one off.
"validation? what validation?"
https://news.ycombinator.com/item?id=27244941
Edit: you should probably read the article I linked first.
Common Raptor Lake L, add it to the pile of oxidation and overvoltage faults. This has to be the most faulty generation in Intel's entire recent manufacturing history.
It's the Alder Lake MAX. Originally decent design just pushed too far.
modifying source to avoid an assembly isntr isn't a fix... this need a compiler fix most likely, or a microcode fix, if possible.
Anyone have knowledge of whether microcode can be patched on consumer grade Intel CPUs?
https://github.com/intel/intel-linux-processor-microcode-dat...
Hot-swappable, even. TIL!
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Yes? It is regularly; both the firmware or the OS can deliver updates depending on configuration. The Raptor Lake CPUs in question have gone through an enormous number of microcode revisions already due to quite famous voltage scaling issues; it's unclear if this errata is fallout from or related to a similar root cause or just another issue with the processor.
At boot time, the following package provides the latest Intel CPU microcode data files on NetBSD.
dmesg shows
Why is this downvoted? (At the time of writing, the text is grey, so it has at least a few downvotes.)
This is a good question. As others have noted below, yes, and sometimes you can see kernel logging on start-up when the microcode is loaded.
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