Re: [PATCH v1] x86/mm/pat: (un)track_pfn_copy() fix + improvements

[Nathan Chancellor <nathan@kernel.org>]

On Mon, Apr 07, 2025 at 08:59:44PM +0200, Ingo Molnar wrote:
> Good, although why is this compiler option named so weirdly in Clang:
> 
>   CC_AUTO_VAR_INIT_ZERO_ENABLER := -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
> 
> Hopefully it is named thusly because Clang has adopted GCC's 
> -ftrivial-auto-var-init=zero?

Clang did -ftrivial-auto-var-init first, where the original author added
both pattern and zero but intended to remove zero once pattern has been
optimized enough compared to zero (if I remember and understand
correctly), so the "enabler" flag was added to try and make that clear.
Eventually, Kees leveraged both Linus's stated desire for initializing
stack variables [1] and GCC 12 landing -ftrivial-auto-var-init=zero
without a separate enable option to deprecate the "enabler" flag in
clang 16 [2] and remove it altogether in clang 18 [3].

[1]: https://lore.kernel.org/CAHk-=wgTM+cN7zyUZacGQDv3DuuoA4LORNPWgb1Y_Z1p4iedNQ@mail.gmail.com/
[2]: https://github.com/llvm/llvm-project/commit/aef03c9b3bed5cef5a1940774b80128aefcb4095
[3]: https://github.com/llvm/llvm-project/commit/00e54d04ae2802d498741097d4b83e898bc99c5b

Cheers,
Nathan