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warn when using an unstable feature with -Ctarget-feature #117616

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merged 2 commits into from
Nov 7, 2023

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@RalfJung RalfJung commented Nov 5, 2023

Setting or unsetting the wrong target features can cause ABI incompatibility (#116344, #116558). We need to carefully audit features for their ABI impact before stabilization. I just learned that we currently accept arbitrary unstable features on stable and if they are in the list of Rust target features, even unstable, then we don't even warn about that!1 That doesn't seem great, so I propose we introduce a warning here.

This has an obvious loophole via -Ctarget-cpu. I'm not sure how to best deal with that, but it seems better to fix what we can and think about the other cases later, maybe once we have a better idea for how to resolve the general mess that are ABI-affecting target features.

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r? @compiler-errors

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@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Nov 5, 2023
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@@ -76,8 +76,8 @@ codegen_llvm_target_machine = could not create LLVM TargetMachine for triple: {$
codegen_llvm_target_machine_with_llvm_err = could not create LLVM TargetMachine for triple: {$triple}: {$llvm_err}

codegen_llvm_unknown_ctarget_feature =
unknown feature specified for `-Ctarget-feature`: `{$feature}`
.note = it is still passed through to the codegen backend
unknown and unstable feature specified for `-Ctarget-feature`: `{$feature}`
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"and"? or "or"?

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"and"

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Why? I don't totally understand how something can both be unknown and unstable.

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If it's unknown it's clearly not stable, and hence it is unstable.

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Why does that need clarification? Like, if it's clearly not stable by virtue of being uknown, why are we saying it's unknown and unstable?

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I think it's worth emphasizing that unknown implies unstable. Unstable has a particular meaning in the Rust context, and that implication is very clear to us, but might not be clear at all to users.

It is extremely unusual that we allow unstable things to even be done on stable Rust, making it even more important to point this out explicitly.

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@bors r+

idk if you intended this to go through an FCP, but it's a warning, and I think the warning is well-justified, so I see no reason for that. you can r- if you disagree, and I can start one.

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bors commented Nov 7, 2023

📌 Commit b85c683 has been approved by compiler-errors

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 7, 2023
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bors commented Nov 7, 2023

⌛ Testing commit b85c683 with merge 43786cf...

bors added a commit to rust-lang-ci/rust that referenced this pull request Nov 7, 2023
…=compiler-errors

warn when using an unstable feature with -Ctarget-feature

Setting or unsetting the wrong target features can cause ABI incompatibility (rust-lang#116344, rust-lang#116558). We need to carefully audit features for their ABI impact before stabilization. I just learned that we currently accept arbitrary unstable features on stable and if they are in the list of Rust target features, even unstable, then we don't even warn about that!1 That doesn't seem great, so I propose we introduce a warning here.

This has an obvious loophole via `-Ctarget-cpu`. I'm not sure how to best deal with that, but it seems better to fix what we can and think about the other cases later, maybe once we have a better idea for how to resolve the general mess that are ABI-affecting target features.
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bors commented Nov 7, 2023

💔 Test failed - checks-actions

@bors bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Nov 7, 2023
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RalfJung commented Nov 7, 2023

@bors r=compiler-errors

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bors commented Nov 7, 2023

📌 Commit 84abf83 has been approved by compiler-errors

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 7, 2023
bors added a commit to rust-lang-ci/rust that referenced this pull request Nov 7, 2023
…iaskrgr

Rollup of 4 pull requests

Successful merges:

 - rust-lang#115485 (Format macro const literals with pretty printer)
 - rust-lang#117616 (warn when using an unstable feature with -Ctarget-feature)
 - rust-lang#117639 (Update books)
 - rust-lang#117675 (llvm-wrapper: Remove include of non-existant Vectorize.h)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit f8c6770 into rust-lang:master Nov 7, 2023
11 checks passed
@rustbot rustbot added this to the 1.75.0 milestone Nov 7, 2023
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Nov 7, 2023
Rollup merge of rust-lang#117616 - RalfJung:unstable-target-features, r=compiler-errors

warn when using an unstable feature with -Ctarget-feature

Setting or unsetting the wrong target features can cause ABI incompatibility (rust-lang#116344, rust-lang#116558). We need to carefully audit features for their ABI impact before stabilization. I just learned that we currently accept arbitrary unstable features on stable and if they are in the list of Rust target features, even unstable, then we don't even warn about that!1 That doesn't seem great, so I propose we introduce a warning here.

This has an obvious loophole via `-Ctarget-cpu`. I'm not sure how to best deal with that, but it seems better to fix what we can and think about the other cases later, maybe once we have a better idea for how to resolve the general mess that are ABI-affecting target features.
@RalfJung RalfJung deleted the unstable-target-features branch November 11, 2023 09:58
celinval added a commit to celinval/rust-dev that referenced this pull request Jun 4, 2024
Update Rust toolchain from nightly-2023-11-07 to nightly-2023-11-08
without any other source changes.
This is an automatically generated pull request. If any of the CI checks
fail, manual intervention is required. In such a case, review the
changes at https://github.com/rust-lang/rust from
rust-lang@189d6c7
up to
rust-lang@7adc89b.
The log for this commit range is:
rust-lang@7adc89b69b Auto merge of
rust-lang#117680 - matthiaskrgr:rollup-kgaa4ma, r=matthiaskrgr
rust-lang@518fe492f1 Rollup merge of
rust-lang#117675 - zmodem:vectorize_h, r=durin42
rust-lang@f6f6fd1d1a Rollup merge of
rust-lang#117639 - rustbot:docs-update, r=ehuss
rust-lang@f8c67704f2 Rollup merge of
rust-lang#117616 - RalfJung:unstable-target-features, r=compiler-errors
rust-lang@cd5b5e08fe Rollup merge of
rust-lang#115485 - DaniPopes:rustdoc-macro-consts, r=jackh726,fmease
rust-lang@118a2deea5 Auto merge of
rust-lang#117617 - Urgau:bump-libc-0.2.150, r=Mark-Simulacrum
rust-lang@84abf837b8 manually bless a
wasm-only test
rust-lang@752a6132e5 llvm-wrapper: Remove
include of non-existant Vectorize.h
rust-lang@9bd71afb90 Auto merge of
rust-lang#115904 - notriddle:notriddle/preload-bold, r=GuillaumeGomez
rust-lang@187d1afa9d Auto merge of
rust-lang#117297 - clubby789:fn-trait-missing-paren, r=TaKO8Ki
rust-lang@61a3eea804 Auto merge of
rust-lang#117229 - matthewjasper:thir-unsafeck-fixes, r=cjgillot
rust-lang@114f1f6838 Auto merge of
rust-lang#117610 - compiler-errors:object-hmm, r=aliemjay
rust-lang@504f63efb0 Auto merge of
rust-lang#117418 - compiler-errors:better_error_body, r=oli-obk
rust-lang@4e0fb98a5c Auto merge of
rust-lang#117006 - estebank:issue-69512, r=compiler-errors
rust-lang@f926031ea5 When not finding
assoc fn on type, look for builder fn
rust-lang@7b97a5ca84 Auto merge of
rust-lang#117511 - gurry:117406-err-packed-structs, r=compiler-errors
rust-lang@5a9f07cc97 Build a better MIR
body when errors are encountered
rust-lang@171d5587ca Don't instantiate
the binder twice when assembling object candidate
rust-lang@24e14dd8b4 Only check
predicates for late-bound non-lifetime vars in object candidate assembly
rust-lang@bf65e3bddb Update books
rust-lang@868de8e76b Visit patterns in
THIR let expressions
rust-lang@2b59992736 Add suggestion to
THIR unsafe_op_in_unsafe_fn lint
rust-lang@2b2c0f9886 Allow tests with
rust-rustfix and revisions
rust-lang@931692fa13 Recognise thread
local statics in THIR unsafeck
rust-lang@b85c6835d0 warn when using an
unstable feature with -Ctarget-feature
rust-lang@15719a8c1d libc: bump
dependency to 0.2.150
rust-lang@4b3ece475d Emit explanatory
note for move errors in packed struct derives
rust-lang@904aceec7d Give a better
diagnostic for missing parens in Fn* bounds
rust-lang@2b858b7eb8 Format macro const
literals with pretty printer
rust-lang@2a92981301 rustdoc: stop
preloading Source Serif 4 Bold

Co-authored-by: celinval <celinval@users.noreply.github.com>
Co-authored-by: Zyad Hassan <88045115+zhassan-aws@users.noreply.github.com>
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