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Add Option to Force Unwind Tables #69984
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src/librustc_session/session.rs
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@@ -593,6 +593,14 @@ impl Session { | |||
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} | |||
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pub fn must_emit_unwind_tables(&self) -> bool { | |||
if let Some(x) = self.opts.cg.force_unwind_tables { |
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As implemented, this allows users to turn off unwinding tables even if the target strictly requires them. That seems like a footgun.
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should we just error in case of such a conflict?
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Emitting an error has prior art in rustc so, yes.
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Ok, Will do when I get back to my work computer.
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I believe that I've done this in the right place: validate_commandline_args_with_session_available
. This check only takes into account the target definition, not the no_landing_pads
that is checked at attribute insertion time.
I'm obviously in favor of having this option in some way, but since |
@rfcbot fcp merge This introduces an insta-stable argument to control a fairly well understood behaviour of the compilers (not just rustc, but also clang/gcc ( |
Team member @nagisa 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! See this document for info about what commands tagged team members can give me. |
As I commented in #69890:
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The job Click to expand the log.
I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact |
@Amanieu Can you elaborate why you think a new
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@bors retry |
@lenary: 🔑 Insufficient privileges: not in try users |
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One advantage of
AFAIK that's not true, when compiling with |
Cargo has its own validation of this Cargo.toml entry, so some Cargo changes are required to enable this. And if Cargo changes are required anyway, I don't think it would be significantly harder to add a new
Ah, right, this is indeed mostly the current behavior. But it is not true for allocator shims, and I don't think the current behavior for other functions is intended or can be expected to last forever. For historic reasons, certain code paths in the compiler currently decide some unwinding-related things based on the global |
Fair enough, I'll withdraw my objection to making this a |
@rfcbot reviewed |
Should we avoid emitting unwind tables by default on Windows (and let people opt-in with this flag)? If not, we probably want an option to turn off unwind tables which this doesn't enable. |
Given the many different mechanisms and tools that rely on SEH, and Windows gurus stating that pretty much all functions should have unwinding information on x64 Windows, it does not seem very wise to ever omit unwinding tables. Even an opt-out seems dubious to me, and as far as I can tell it's not a feature anyone has ever requested. In fact, after poking at it for a little bit, I can't find any such opt out in MSVC, even when compiling plain C code. In any case, should we ever change our mind about this, we can still change |
My understanding is that the I don't know if i should include that check in the error reporting here: https://github.com/rust-lang/rust/pull/69984/files#diff-eadaa1c9e135801995ae29eaec608049R1173 - happy to update the patch to do so if needed, not sure how it will affect testing. |
I'm pretty sure this is wrong. However, your conclusion (that users can't remove unwinding information on Windows targets) is correct as far as I can tell. |
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Thanks! @bors r+ |
📌 Commit 7f098f637f8efe817ecca975baa9dd71ce018a4f has been approved by |
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When panic != unwind, `nounwind` is added to all functions for a target. This can cause issues when a panic happens with RUST_BACKTRACE=1, as there needs to be a way to reconstruct the backtrace. There are three possible sources of this information: forcing frame pointers (for which an option exists already), debug info (for which an option exists), or unwind tables. Especially for embedded devices, forcing frame pointers can have code size overheads (RISC-V sees ~10% overheads, ARM sees ~2-3% overheads). In code, it can be the case that debug info is not kept, so it is useful to provide this third option, unwind tables, that users can use to reconstruct the call stack. Reconstructing this stack is harder than with frame pointers, but it is still possible. This commit adds a compiler option which allows a user to force the addition of unwind tables. Unwind tables cannot be disabled on targets that require them for correctness, or when using `-C panic=unwind`.
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@bors r+ |
📌 Commit cda9946 has been approved by |
⌛ Testing commit cda9946 with merge 753f25e628b9556fd0e963a1027b3883b17d450c... |
…na-kruppe Add Option to Force Unwind Tables When panic != unwind, `nounwind` is added to all functions for a target. This can cause issues when a panic happens with RUST_BACKTRACE=1, as there needs to be a way to reconstruct the backtrace. There are three possible sources of this information: forcing frame pointers (for which an option exists already), debug info (for which an option exists), or unwind tables. Especially for embedded devices, forcing frame pointers can have code size overheads (RISC-V sees ~10% overheads, ARM sees ~2-3% overheads). In production code, it can be the case that debug info is not kept, so it is useful to provide this third option, unwind tables, that users can use to reconstruct the call stack. Reconstructing this stack is harder than with frame pointers, but it is still possible. --- This came up in discussion on rust-lang#69890, and turned out to be a fairly simple addition. r? @hanna-kruppe
💔 Test failed - checks-azure |
Seems spurious, @bors retry |
⌛ Testing commit cda9946 with merge ac9bfbf737b9450ab6f6e632406e3a403b4e958a... |
@bors retry |
Rollup of 4 pull requests Successful merges: - rust-lang#69984 (Add Option to Force Unwind Tables) - rust-lang#71830 (Remove clippy from some leftover lists of "possibly failing" tools) - rust-lang#71894 (Suggest removing semicolon in last expression only if it's type is known) - rust-lang#71897 (Improve docs for embed-bitcode and linker-plugin-lto) Failed merges: r? @ghost
While here clean up all pkglint warnings. Changes since 1.44.1: Version 1.45.2 (2020-08-03) ========================== * [Fix bindings in tuple struct patterns][74954] * [Fix track_caller integration with trait objects][74784] [74954]: rust-lang/rust#74954 [74784]: rust-lang/rust#74784 Version 1.45.1 (2020-07-30) ========================== * [Fix const propagation with references.][73613] * [rustfmt accepts rustfmt_skip in cfg_attr again.][73078] * [Avoid spurious implicit region bound.][74509] * [Install clippy on x.py install][74457] [73613]: rust-lang/rust#73613 [73078]: rust-lang/rust#73078 [74509]: rust-lang/rust#74509 [74457]: rust-lang/rust#74457 Version 1.45.0 (2020-07-16) ========================== Language -------- - [Out of range float to int conversions using `as` has been defined as a saturating conversion.][71269] This was previously undefined behaviour, but you can use the `{f64, f32}::to_int_unchecked` methods to continue using the current behaviour, which may be desirable in rare performance sensitive situations. - [`mem::Discriminant<T>` now uses `T`'s discriminant type instead of always using `u64`.][70705] - [Function like procedural macros can now be used in expression, pattern, and statement positions.][68717] This means you can now use a function-like procedural macro anywhere you can use a declarative (`macro_rules!`) macro. Compiler -------- - [You can now override individual target features through the `target-feature` flag.][72094] E.g. `-C target-feature=+avx2 -C target-feature=+fma` is now equivalent to `-C target-feature=+avx2,+fma`. - [Added the `force-unwind-tables` flag.][69984] This option allows rustc to always generate unwind tables regardless of panic strategy. - [Added the `embed-bitcode` flag.][71716] This codegen flag allows rustc to include LLVM bitcode into generated `rlib`s (this is on by default). - [Added the `tiny` value to the `code-model` codegen flag.][72397] - [Added tier 3 support\* for the `mipsel-sony-psp` target.][72062] - [Added tier 3 support for the `thumbv7a-uwp-windows-msvc` target.][72133] \* Refer to Rust's [platform support page][forge-platform-support] for more information on Rust's tiered platform support. Libraries --------- - [`net::{SocketAddr, SocketAddrV4, SocketAddrV6}` now implements `PartialOrd` and `Ord`.][72239] - [`proc_macro::TokenStream` now implements `Default`.][72234] - [You can now use `char` with `ops::{Range, RangeFrom, RangeFull, RangeInclusive, RangeTo}` to iterate over a range of codepoints.][72413] E.g. you can now write the following; ```rust for ch in 'a'..='z' { print!("{}", ch); } println!(); // Prints "abcdefghijklmnopqrstuvwxyz" ``` - [`OsString` now implements `FromStr`.][71662] - [The `saturating_neg` method as been added to all signed integer primitive types, and the `saturating_abs` method has been added for all integer primitive types.][71886] - [`Arc<T>`, `Rc<T>` now implement `From<Cow<'_, T>>`, and `Box` now implements `From<Cow>` when `T` is `[T: Copy]`, `str`, `CStr`, `OsStr`, or `Path`.][71447] - [`Box<[T]>` now implements `From<[T; N]>`.][71095] - [`BitOr` and `BitOrAssign` are implemented for all `NonZero` integer types.][69813] - [The `fetch_min`, and `fetch_max` methods have been added to all atomic integer types.][72324] - [The `fetch_update` method has been added to all atomic integer types.][71843] Stabilized APIs --------------- - [`Arc::as_ptr`] - [`BTreeMap::remove_entry`] - [`Rc::as_ptr`] - [`rc::Weak::as_ptr`] - [`rc::Weak::from_raw`] - [`rc::Weak::into_raw`] - [`str::strip_prefix`] - [`str::strip_suffix`] - [`sync::Weak::as_ptr`] - [`sync::Weak::from_raw`] - [`sync::Weak::into_raw`] - [`char::UNICODE_VERSION`] - [`Span::resolved_at`] - [`Span::located_at`] - [`Span::mixed_site`] - [`unix::process::CommandExt::arg0`] Cargo ----- Misc ---- - [Rustdoc now supports strikethrough text in Markdown.][71928] E.g. `~~outdated information~~` becomes "~~outdated information~~". - [Added an emoji to Rustdoc's deprecated API message.][72014] Compatibility Notes ------------------- - [Trying to self initialize a static value (that is creating a value using itself) is unsound and now causes a compile error.][71140] - [`{f32, f64}::powi` now returns a slightly different value on Windows.][73420] This is due to changes in LLVM's intrinsics which `{f32, f64}::powi` uses. - [Rustdoc's CLI's extra error exit codes have been removed.][71900] These were previously undocumented and not intended for public use. Rustdoc still provides a non-zero exit code on errors. Internals Only -------------- - [Make clippy a git subtree instead of a git submodule][70655] - [Unify the undo log of all snapshot types][69464] [73420]: rust-lang/rust#73420 [72324]: rust-lang/rust#72324 [71843]: rust-lang/rust#71843 [71886]: rust-lang/rust#71886 [72234]: rust-lang/rust#72234 [72239]: rust-lang/rust#72239 [72397]: rust-lang/rust#72397 [72413]: rust-lang/rust#72413 [72014]: rust-lang/rust#72014 [72062]: rust-lang/rust#72062 [72094]: rust-lang/rust#72094 [72133]: rust-lang/rust#72133 [71900]: rust-lang/rust#71900 [71928]: rust-lang/rust#71928 [71662]: rust-lang/rust#71662 [71716]: rust-lang/rust#71716 [71447]: rust-lang/rust#71447 [71269]: rust-lang/rust#71269 [71095]: rust-lang/rust#71095 [71140]: rust-lang/rust#71140 [70655]: rust-lang/rust#70655 [70705]: rust-lang/rust#70705 [69984]: rust-lang/rust#69984 [69813]: rust-lang/rust#69813 [69464]: rust-lang/rust#69464 [68717]: rust-lang/rust#68717 [`Arc::as_ptr`]: https://doc.rust-lang.org/stable/std/sync/struct.Arc.html#method.as_ptr [`BTreeMap::remove_entry`]: https://doc.rust-lang.org/stable/std/collections/struct.BTreeMap.html#method.remove_entry [`Rc::as_ptr`]: https://doc.rust-lang.org/stable/std/rc/struct.Rc.html#method.as_ptr [`rc::Weak::as_ptr`]: https://doc.rust-lang.org/stable/std/rc/struct.Weak.html#method.as_ptr [`rc::Weak::from_raw`]: https://doc.rust-lang.org/stable/std/rc/struct.Weak.html#method.from_raw [`rc::Weak::into_raw`]: https://doc.rust-lang.org/stable/std/rc/struct.Weak.html#method.into_raw [`sync::Weak::as_ptr`]: https://doc.rust-lang.org/stable/std/sync/struct.Weak.html#method.as_ptr [`sync::Weak::from_raw`]: https://doc.rust-lang.org/stable/std/sync/struct.Weak.html#method.from_raw [`sync::Weak::into_raw`]: https://doc.rust-lang.org/stable/std/sync/struct.Weak.html#method.into_raw [`str::strip_prefix`]: https://doc.rust-lang.org/stable/std/primitive.str.html#method.strip_prefix [`str::strip_suffix`]: https://doc.rust-lang.org/stable/std/primitive.str.html#method.strip_suffix [`char::UNICODE_VERSION`]: https://doc.rust-lang.org/stable/std/char/constant.UNICODE_VERSION.html [`Span::resolved_at`]: https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.resolved_at [`Span::located_at`]: https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.located_at [`Span::mixed_site`]: https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.mixed_site [`unix::process::CommandExt::arg0`]: https://doc.rust-lang.org/std/os/unix/process/trait.CommandExt.html#tymethod.arg0
When panic != unwind,
nounwind
is added to all functions for a target.This can cause issues when a panic happens with RUST_BACKTRACE=1, as
there needs to be a way to reconstruct the backtrace. There are three
possible sources of this information: forcing frame pointers (for which
an option exists already), debug info (for which an option exists), or
unwind tables.
Especially for embedded devices, forcing frame pointers can have code
size overheads (RISC-V sees ~10% overheads, ARM sees ~2-3% overheads).
In production code, it can be the case that debug info is not kept, so it is useful
to provide this third option, unwind tables, that users can use to
reconstruct the call stack. Reconstructing this stack is harder than
with frame pointers, but it is still possible.
This came up in discussion on #69890, and turned out to be a fairly simple addition.
r? @hanna-kruppe