Re: [PATCH v3 3/3] arm64, compiler-context-analysis: Permit alias analysis through __READ_ONCE() with CONFIG_LTO=y
From: Marco Elver <elver@google.com>
Date: 2026-02-04 10:46:40
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On Tue, 3 Feb 2026 at 12:47, Will Deacon [off-list ref] wrote: [...]
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What does GCC do with this? :/GCC currently doesn't see it, LTO is clang only.LTO is just one way that a compiler could end up breaking dependency chains, so I really want to maintain the option to enable this path for GCC in case we run into problems caused by other optimisations in future.
It will work for GCC, but only from GCC 11. Before that __auto_type does not drop qualifiers: https://godbolt.org/z/sc5bcnzKd (switch to GCC 11 to see it compile) So to summarize, all supported Clang versions deal with __auto_type correctly for the fallback; GCC from version 11 does (kernel currently supports GCC 8 and above). From GCC 14 and Clang 19 we have __typeof_unqual__. I really don't see another way forward; there's no other good way to solve this issue. I would advise against pessimizing new compilers and features because maybe one day we might still want to enable this version of READ_ONCE() for GCC 8-10. Should we one day choose to enable this READ_ONCE() version for GCC, we will (a) either have bumped the minimum GCC version to 11+, or (b) we can only do so from GCC 11. At this point GCC 11 was released 5 years ago!