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Stabilize const_maybe_uninit_zeroed and const_mem_zeroed #116218

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merged 2 commits into from
Nov 5, 2023

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tgross35
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@tgross35 tgross35 commented Sep 28, 2023

Make MaybeUninit::zeroed and mem::zeroed const stable. Newly stable API:

// core::mem
pub const unsafe fn zeroed<T>() ->;

impl<T> MaybeUninit<T> {
    pub const fn zeroed() -> MaybeUninit<T>;
}

This relies on features based around const_mut_refs. Per @RalfJung, this should be OK since we do not leak any &mut to the user.

For this to be possible, intrinsics assert_zero_valid and assert_mem_uninitialized_valid were made const stable.

Tracking issue: #91850
Zulip discussion: https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/topic/.60const_mut_refs.60.20dependents

r? libs-api
@rustbot label -T-libs +T-libs-api +A-const-eval
cc @RalfJung @oli-obk @rust-lang/wg-const-eval

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. A-const-eval Area: Constant evaluation (MIR interpretation) T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. labels Sep 28, 2023
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@rustbot label -T-libs

@rustbot rustbot removed the T-libs Relevant to the library team, which will review and decide on the PR/issue. label Sep 28, 2023
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cc implementer @lilasta

@RalfJung RalfJung added the T-lang Relevant to the language team, which will review and decide on the PR/issue. label Sep 28, 2023
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LGTM, but the FCP should probably include t-lang since this makes the internal mutable referece/ptr support in our const-eval engine accessible from stable for the first time. I'm not at all concerned about doing so (that support is very mature), but it's worth a bit of extra scrutiny.

@dtolnay dtolnay added the needs-fcp This change is insta-stable, so needs a completed FCP to proceed. label Sep 28, 2023
@dtolnay dtolnay assigned dtolnay and unassigned BurntSushi Sep 28, 2023
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dtolnay commented Sep 28, 2023

@rfcbot fcp merge

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rfcbot commented Sep 28, 2023

Team member @dtolnay has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

@rfcbot rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Sep 28, 2023
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scottmcm commented Sep 29, 2023

Should we make https://doc.rust-lang.org/std/mem/fn.zeroed.html const at the same time, since it's a simple wrapper?

But either way, no concerns from me about doing this. Letting people have a zeroinitializer easily makes sense.

@rfcbot reviewed

(And we could easily add an intrinsic to get a zeroed value if for some reason we had to stop using &mut in the implementation of this for a while.)

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Should we make https://doc.rust-lang.org/std/mem/fn.zeroed.html const at the same time, since it's a simple wrapper?

Sure, why not.

///
/// static PLUGIN_LIST: [PluginInfo; 2] = [
/// PluginInfo { id: 1, action: Some(|x| x + 5) },
/// unsafe { MaybeUninit::zeroed().assume_init() }
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nit: could we find a better example? This could be PluginInfo { id: 0, action: None }, which is both shorter and doesn't need unsafe.

(And please put a // SAFETY: … comment on any unsafe { … } used in examples, to encourage good behaviour and explain why it's not UB.)

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Sure, any suggestions? I was struggling to come up with something better, null-terminated arrays for plugins are just the use case I always come across

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The entire problem with a good example here is that you use zeroed when the full thing would be a pain to write or even look at. So usually that means that you're talking about some type with 50 integer fields or something. But regardless of details it's "something so big it doesn't fit in a 2 line example".

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Are we able to use dev dependencies? Is there a libc use case to feature here?

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@lilasta lilasta Nov 4, 2023

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I think that a generic function can be a good example.

#![feature(const_maybe_uninit_zeroed)]

use core::mem::MaybeUninit;

struct Time32(u32);
struct Time64(u64);
struct Time<T>(T);

// I couldn't come up with a good name. Zeroable?
trait SafeZeroed {}

impl SafeZeroed for Time32 {}
impl SafeZeroed for Time64 {}
impl<T: SafeZeroed> SafeZeroed for Time<T> {}

const fn time_zeroed<T>() -> Time<T>
where
    Time<T>: SafeZeroed,
{
    unsafe { MaybeUninit::zeroed().assume_init() }
}

(Well, in this example it makes more sense to define a trait that has TimeTrait::zeroed, etc...)

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SafeZeroed would actually have to be an unsafe trait in this scenario.

Honestly I don't think we need example code on this particular function/method. It makes the all-zeroed value, that's already extremely simple I think.

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I really just wanted a sanity check test for the functionality, but agree it’s redundant as an example. And that usually it’s with pretty big C structs for plugins, so there isn’t really a good minimal example. I’ll remove the example and change it to a unit test.

(Not in front of a computer now but I will do it tomorrow)

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Nevermind, I was able to do it now

@dtolnaybot ready 🙂

@tgross35 tgross35 changed the title Stabilize const_maybe_uninit_zeroed Stabilize const_maybe_uninit_zeroed and const_mem_zeroed Sep 29, 2023
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I updated this PR to do mem::zeroed as well. It depends on intrinsic assert_zero_valid becoming const, I assumed that isn't a problem either.

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Yeah, assert_inhabited, assert_zero_valid, assert_mem_uninitialized_valid are very similar and can just all be made stably const (since assert_inhabited already is stably const).

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Even easier 🙂 I added assert_mem_uninitialized_valid

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@tgross35 tgross35 force-pushed the const-maybe-uninit-zeroed branch 2 times, most recently from 8315295 to 87cea7b Compare September 29, 2023 07:32
@dtolnay dtolnay removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 15, 2023
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 11, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 12, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 12, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 12, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 12, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 12, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 12, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 12, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 12, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 13, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 13, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 13, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 13, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 13, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 13, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 14, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 14, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 14, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 14, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 14, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 14, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 14, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 14, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 15, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 15, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 15, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
kuba-moo pushed a commit to linux-netdev/testing that referenced this pull request Dec 15, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: NipaLocal <nipa@local>
intel-lab-lkp pushed a commit to intel-lab-lkp/linux that referenced this pull request Dec 15, 2023
This patch adds abstractions to implement network PHY drivers; the
driver registration and bindings for some of callback functions in
struct phy_driver and many genphy_ functions.

This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.

This patch enables unstable const_maybe_uninit_zeroed feature for
kernel crate to enable unsafe code to handle a constant value with
uninitialized data. With the feature, the abstractions can initialize
a phy_driver structure with zero easily; instead of initializing all
the members by hand. It's supposed to be stable in the not so distant
future.

Link: rust-lang/rust#116218

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Comment on lines +570 to +584
fn const_maybe_uninit_zeroed() {
// Sanity check for `MaybeUninit::zeroed` in a realistic const situation (plugin array term)
#[repr(C)]
struct Foo {
a: Option<&'static str>,
b: Bar,
c: f32,
d: *const u8,
}
#[repr(C)]
struct Bar(usize);
struct FooPtr(*const Foo);
unsafe impl Sync for FooPtr {}

static UNINIT: FooPtr = FooPtr([unsafe { MaybeUninit::zeroed().assume_init() }].as_ptr());
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I'm not sure what motivated this test but there actually isn't any guarantee that all-zero bytes are a valid value for Option<&'static str> since that's a fat pointer.

NPO is only guaranteed for thin pointers

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Yeah but just because there is no guarantee doesn't mean we should have no test.

Or put differently, library and ui tests are a rustc implementation detail and not source for stable guarantees. Only docs are stable guarantees.

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Also we should make that a docs guarantee for &str, as a separate future PR

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That'd conflict with niches-for-metadata that I'm working on. The length field will have a larger niche which means it becomes preferred by the layout algorithm and Option::None is no longer zero but some other value.
That's how I found this.

Or put differently, library and ui tests are a rustc implementation detail and not source for stable guarantees.

I mean that this looks like it has been inspired by some real code and that that code is suspect.

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That sounds extremely unfortunate and that a special case should be put back in or something. But we can go into that on zulip or whatever PR you open.

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This test was just a sanity check that it does indeed do the right thing. I suppose &str might not have been the best optional reference, but that specific choice wasn't motivated by any real code.

Otoh, it should still zero everything even if invalid, even if Miri one day starts flagging this test.

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error[E0080]: it is undefined behavior to use this value
   --> library/core/tests/mem.rs:789:5
    |
789 |     static UNINIT: FooPtr = FooPtr([unsafe { MaybeUninit::zeroed().assume_init() }].as_ptr());
    |     ^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>[0].a.<enum-variant(Some)>.0: encountered a null reference
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
    = note: the raw bytes of the constant (size: 8, align: 8) {
                ╾───alloc7286<imm>────╼                         │ ╾──────╼
            }

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Otoh, it should still zero everything even if invalid, even if Miri one day starts flagging this test.

...or the compiler itself I suppose. Feel free to change or #[allow(...)] this test as needed, as long as there isn't any risk of something like MaybeUninit::zeroed()'s output later being fixed up with a non-zero niche in the pointer metadata (seems unlikely)

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Even if we never guaranteed NPO for wide pointers, changing that seems very risky and I expect it will break some unsafe code out there. Most people won't expect such a discontinuity between thin and wide ptrs.

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Turns out the actual problem with this test is that it is UB because the type has padding, so the memory will not be all-zeroes after being returned by assume_init(). ;)

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