Add asm goto support to `asm!` #119365

nbdd0121 · 2023-12-27T23:13:41Z

Tracking issue: #119364

This PR implements asm-goto support, using the syntax described in "future possibilities" section of RFC2873.

Currently I have only implemented the label part, not the fallthrough part (i.e. fallthrough is implicit). This doesn't reduce the expressive though, since you can use label-break to get arbitrary control flow or simply set a value and rely on jump threading optimisation to get the desired control flow. I can add that later if deemed necessary.

r? @Amanieu
cc @ojeda

rustbot · 2023-12-27T23:13:50Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @davidtwco, @celinval, @vakaras

rustbot · 2023-12-27T23:40:08Z

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

rustbot · 2023-12-28T03:05:15Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

compiler/rustc_const_eval/src/interpret/terminator.rs

Amanieu

This needs a page in the unstable book. It should contain everything that needs to be added to the inline asm page in the reference when this is eventually stabilized.

compiler/rustc_hir_typeck/src/expr.rs

compiler/rustc_middle/src/mir/syntax.rs

compiler/rustc_codegen_llvm/src/asm.rs

compiler/rustc_codegen_ssa/src/mir/block.rs

Amanieu · 2024-01-02T19:24:29Z

src/doc/unstable-book/src/language-features/asm-goto.md

+}
+```
+
+The block must have unit type.


This should be updated to clarify the behavior of diverging blocks, and how this interacts with noreturn.

Amanieu · 2024-01-02T19:25:36Z

tests/ui/asm/x86_64/goto.rs

+
+// asm goto with outputs cause miscompilation in LLVM. UB can be triggered
+// when outputs are used inside the label block when optimisation is enabled.
+// See: https://github.com/llvm/llvm-project/issues/74483


This is a blocker for stabilizing this feature.

bors · 2024-01-05T19:29:43Z

☔ The latest upstream changes (presumably #119621) made this pull request unmergeable. Please resolve the merge conflicts.

This makes more sense because most cases then second one is unwind target.

RalfJung · 2024-03-04T18:51:45Z

@bors r- (PR requeued by sync)

Amanieu · 2024-03-07T11:54:39Z

@bors r+

bors · 2024-03-07T11:54:41Z

📌 Commit 05a549b has been approved by Amanieu

It is now in the queue for this repository.

nbdd0121 · 2024-03-07T11:58:00Z

Sorry, mistakenly committed library/stdarch..

Amanieu · 2024-03-07T11:58:41Z

@bors r+

bors · 2024-03-07T11:58:43Z

📌 Commit 0ee0f29 has been approved by Amanieu

It is now in the queue for this repository.

Add asm goto support to `asm!` Tracking issue: rust-lang#119364 This PR implements asm-goto support, using the syntax described in "future possibilities" section of [RFC2873](https://rust-lang.github.io/rfcs/2873-inline-asm.html#asm-goto). Currently I have only implemented the `label` part, not the `fallthrough` part (i.e. fallthrough is implicit). This doesn't reduce the expressive though, since you can use label-break to get arbitrary control flow or simply set a value and rely on jump threading optimisation to get the desired control flow. I can add that later if deemed necessary. r? `@Amanieu` cc `@ojeda`

…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#118623 (Improve std::fs::read_to_string example) - rust-lang#119365 (Add asm goto support to `asm!`) - rust-lang#120608 (Docs for std::ptr::slice_from_raw_parts) - rust-lang#121885 (Move generic `NonZero` `rustc_layout_scalar_valid_range_start` attribute to inner type.) - rust-lang#121938 (Fix quadratic behavior of repeated vectored writes) - rust-lang#122099 (Add `#[inline]` to `BTreeMap::new` constructor) - rust-lang#122143 (PassWrapper: update for llvm/llvm-project@a3319371970b) Failed merges: - rust-lang#122076 (Tweak the way we protect in-place function arguments in interpreters) r? `@ghost` `@rustbot` modify labels: rollup

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#118623 (Improve std::fs::read_to_string example) - rust-lang#119365 (Add asm goto support to `asm!`) - rust-lang#120608 (Docs for std::ptr::slice_from_raw_parts) - rust-lang#121832 (Add new Tier-3 target: `loongarch64-unknown-linux-musl`) - rust-lang#121938 (Fix quadratic behavior of repeated vectored writes) - rust-lang#122099 (Add `#[inline]` to `BTreeMap::new` constructor) - rust-lang#122103 (Make TAITs and ATPITs capture late-bound lifetimes in scope) - rust-lang#122143 (PassWrapper: update for llvm/llvm-project@a3319371970b) Failed merges: - rust-lang#122076 (Tweak the way we protect in-place function arguments in interpreters) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#119365 - nbdd0121:asm-goto, r=Amanieu Add asm goto support to `asm!` Tracking issue: rust-lang#119364 This PR implements asm-goto support, using the syntax described in "future possibilities" section of [RFC2873](https://rust-lang.github.io/rfcs/2873-inline-asm.html#asm-goto). Currently I have only implemented the `label` part, not the `fallthrough` part (i.e. fallthrough is implicit). This doesn't reduce the expressive though, since you can use label-break to get arbitrary control flow or simply set a value and rely on jump threading optimisation to get the desired control flow. I can add that later if deemed necessary. r? ``@Amanieu`` cc ``@ojeda``

Add asm goto support to `asm!` Tracking issue: rust-lang#119364 This PR implements asm-goto support, using the syntax described in "future possibilities" section of [RFC2873](https://rust-lang.github.io/rfcs/2873-inline-asm.html#asm-goto). Currently I have only implemented the `label` part, not the `fallthrough` part (i.e. fallthrough is implicit). This doesn't reduce the expressive though, since you can use label-break to get arbitrary control flow or simply set a value and rely on jump threading optimisation to get the desired control flow. I can add that later if deemed necessary. r? ``@Amanieu`` cc ``@ojeda``

This is the next upgrade to the Rust toolchain, from 1.77.1 to 1.78.0 (i.e. the latest) [1]. See the upgrade policy [2] and the comments on the first upgrade in commit 3ed03f4 ("rust: upgrade to Rust 1.68.2"). # Unstable features There have been no changes to the set of unstable features used in our own code. Therefore, the only unstable features allowed to be used outside the `kernel` crate is still `new_uninit`. However, since we are finally dropping our `alloc` fork [3], all the unstable features used by `alloc` (~30 language ones, ~60 library ones) are not a concern anymore. This reduces the maintanance burden, increases the chances of new compiler versions working without changes and gets us closer to the goal of supporting several compiler versions. It also means that, ignoring non-language/library features, we are currently left with just the few language features needed to implement the kernel `Arc`, the `new_uninit` library feature, the `compiler_builtins` marker and the few `no_*` `cfg`s we pass when compiling `core`/`alloc`. Please see [4] for details. # Required changes ## LLVM's data layout Rust 1.77.0 (i.e. the previous upgrade) introduced a check for matching LLVM data layouts [5]. Then, Rust 1.78.0 upgraded LLVM's bundled major version from 17 to 18 [6], which changed the data layout in x86 [7]. Thus update the data layout in our custom target specification for x86 so that the compiler does not complain about the mismatch: error: data-layout for target `target-5559158138856098584`, `e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128`, differs from LLVM target's `x86_64-linux-gnu` default layout, `e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128` In the future, the goal is to drop the custom target specification files. Meanwhile, if we want to support other LLVM versions used in `rustc` (e.g. for LTO), we will need to add some extra logic (e.g. conditional on LLVM's version, or extracting the data layout from an existing built-in target specification). ## `unused_imports` Rust's `unused_imports` lint covers both unused and redudant imports. Now, in 1.78.0, the lint detects more cases of redundant imports [8]. Thus the previous commit cleaned them up. ## Clippy's `new_without_default` Clippy now suggests to implement `Default` even when `new()` is `const`, since `Default::default()` may call `const` functions even if it is not `const` itself [9]. Thus the previous commit added the implementation. # Other changes in Rust Rust 1.78.0 introduces `feature(asm_goto)` [10] [11]. This feature was discussed in the past [12]. Rust 1.78.0 introduced support for mutable pointers to Rust statics, including a test case for the Linux kernel's `VTABLE` use case [13]. Rust 1.78.0 with debug assertions enabled (i.e. `-Cdebug-assertions=y`, kernel's `CONFIG_RUST_DEBUG_ASSERTIONS=y`) will now always check all unsafe preconditions, without a way to opt-out for particular cases [14]. Rust 1.78.0 also improved a couple issues we reported when giving feedback for the new `--check-cfg` feature [15] [16]. # `alloc` upgrade and reviewing As mentioned above, compiler upgrades will not update `alloc` anymore, since we are dropping our `alloc` fork [3]. As a bonus, even if that series is not applied, the new compiler release happens to build cleanly the existing `alloc` too (i.e. the previous version's). Link: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1770-2024-03-21 [1] Link: https://rust-for-linux.com/rust-version-policy [2] Link: https://lore.kernel.org/rust-for-linux/20240328013603.206764-1-wedsonaf@gmail.com/ [3] Link: Rust-for-Linux#2 [4] Link: rust-lang/rust#120062 [5] Link: rust-lang/rust#120055 [6] Link: https://reviews.llvm.org/D86310 [7] Link: rust-lang/rust#117772 [8] Link: rust-lang/rust-clippy#10903 [9] Link: rust-lang/rust#119365 [10] Link: rust-lang/rust#119364 [11] Link: https://lore.kernel.org/rust-for-linux/ZWipTZysC2YL7qsq@Boquns-Mac-mini.home/ [12] Link: rust-lang/rust#120932 [13] Link: rust-lang/rust#120969 [14] Link: rust-lang/rust#121202 [15] Link: rust-lang/rust#121237 [16] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

This is the next upgrade to the Rust toolchain, from 1.77.1 to 1.78.0 (i.e. the latest) [1]. See the upgrade policy [2] and the comments on the first upgrade in commit 3ed03f4 ("rust: upgrade to Rust 1.68.2"). # Unstable features There have been no changes to the set of unstable features used in our own code. Therefore, the only unstable features allowed to be used outside the `kernel` crate is still `new_uninit`. However, since we are finally dropping our `alloc` fork [3], all the unstable features used by `alloc` (~30 language ones, ~60 library ones) are not a concern anymore. This reduces the maintenance burden, increases the chances of new compiler versions working without changes and gets us closer to the goal of supporting several compiler versions. It also means that, ignoring non-language/library features, we are currently left with just the few language features needed to implement the kernel `Arc`, the `new_uninit` library feature, the `compiler_builtins` marker and the few `no_*` `cfg`s we pass when compiling `core`/`alloc`. Please see [4] for details. # Required changes ## LLVM's data layout Rust 1.77.0 (i.e. the previous upgrade) introduced a check for matching LLVM data layouts [5]. Then, Rust 1.78.0 upgraded LLVM's bundled major version from 17 to 18 [6], which changed the data layout in x86 [7]. Thus update the data layout in our custom target specification for x86 so that the compiler does not complain about the mismatch: error: data-layout for target `target-5559158138856098584`, `e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128`, differs from LLVM target's `x86_64-linux-gnu` default layout, `e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128` In the future, the goal is to drop the custom target specification files. Meanwhile, if we want to support other LLVM versions used in `rustc` (e.g. for LTO), we will need to add some extra logic (e.g. conditional on LLVM's version, or extracting the data layout from an existing built-in target specification). ## `unused_imports` Rust's `unused_imports` lint covers both unused and redundant imports. Now, in 1.78.0, the lint detects more cases of redundant imports [8]. Thus one of the previous patches cleaned them up. ## Clippy's `new_without_default` Clippy now suggests to implement `Default` even when `new()` is `const`, since `Default::default()` may call `const` functions even if it is not `const` itself [9]. Thus one of the previous patches implemented it. # Other changes in Rust Rust 1.78.0 introduced `feature(asm_goto)` [10] [11]. This feature was discussed in the past [12]. Rust 1.78.0 introduced support for mutable pointers to Rust statics, including a test case for the Linux kernel's `VTABLE` use case [13]. Rust 1.78.0 with debug assertions enabled (i.e. `-Cdebug-assertions=y`, kernel's `CONFIG_RUST_DEBUG_ASSERTIONS=y`) now always checks all unsafe preconditions, without a way to opt-out for particular cases [14]. Rust 1.78.0 also improved a couple issues we reported when giving feedback for the new `--check-cfg` feature [15] [16]. # `alloc` upgrade and reviewing As mentioned above, compiler upgrades will not update `alloc` anymore, since we are dropping our `alloc` fork [3]. Link: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1780-2024-05-02 [1] Link: https://rust-for-linux.com/rust-version-policy [2] Link: https://lore.kernel.org/rust-for-linux/20240328013603.206764-1-wedsonaf@gmail.com/ [3] Link: Rust-for-Linux#2 [4] Link: rust-lang/rust#120062 [5] Link: rust-lang/rust#120055 [6] Link: https://reviews.llvm.org/D86310 [7] Link: rust-lang/rust#117772 [8] Link: rust-lang/rust-clippy#10903 [9] Link: rust-lang/rust#119365 [10] Link: rust-lang/rust#119364 [11] Link: https://lore.kernel.org/rust-for-linux/ZWipTZysC2YL7qsq@Boquns-Mac-mini.home/ [12] Link: rust-lang/rust#120932 [13] Link: rust-lang/rust#120969 [14] Link: rust-lang/rust#121202 [15] Link: rust-lang/rust#121237 [16] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

This is the next upgrade to the Rust toolchain, from 1.77.1 to 1.78.0 (i.e. the latest) [1]. See the upgrade policy [2] and the comments on the first upgrade in commit 3ed03f4 ("rust: upgrade to Rust 1.68.2"). # Unstable features There have been no changes to the set of unstable features used in our own code. Therefore, the only unstable features allowed to be used outside the `kernel` crate is still `new_uninit`. However, since we are finally dropping our `alloc` fork [3], all the unstable features used by `alloc` (~30 language ones, ~60 library ones) are not a concern anymore. This reduces the maintenance burden, increases the chances of new compiler versions working without changes and gets us closer to the goal of supporting several compiler versions. It also means that, ignoring non-language/library features, we are currently left with just the few language features needed to implement the kernel `Arc`, the `new_uninit` library feature, the `compiler_builtins` marker and the few `no_*` `cfg`s we pass when compiling `core`/`alloc`. Please see [4] for details. # Required changes ## LLVM's data layout Rust 1.77.0 (i.e. the previous upgrade) introduced a check for matching LLVM data layouts [5]. Then, Rust 1.78.0 upgraded LLVM's bundled major version from 17 to 18 [6], which changed the data layout in x86 [7]. Thus update the data layout in our custom target specification for x86 so that the compiler does not complain about the mismatch: error: data-layout for target `target-5559158138856098584`, `e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128`, differs from LLVM target's `x86_64-linux-gnu` default layout, `e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128` In the future, the goal is to drop the custom target specifications. Meanwhile, if we want to support other LLVM versions used in `rustc` (e.g. for LTO), we will need to add some extra logic (e.g. conditional on LLVM's version, or extracting the data layout from an existing built-in target specification). ## `unused_imports` Rust's `unused_imports` lint covers both unused and redundant imports. Now, in 1.78.0, the lint detects more cases of redundant imports [8]. Thus one of the previous patches cleaned them up. ## Clippy's `new_without_default` Clippy now suggests to implement `Default` even when `new()` is `const`, since `Default::default()` may call `const` functions even if it is not `const` itself [9]. Thus one of the previous patches implemented it. # Other changes in Rust Rust 1.78.0 introduced `feature(asm_goto)` [10] [11]. This feature was discussed in the past [12]. Rust 1.78.0 introduced support for mutable pointers to Rust statics, including a test case for the Linux kernel's `VTABLE` use case [13]. Rust 1.78.0 with debug assertions enabled (i.e. `-Cdebug-assertions=y`, kernel's `CONFIG_RUST_DEBUG_ASSERTIONS=y`) now always checks all unsafe preconditions, without a way to opt-out for particular cases [14]. Rust 1.78.0 also improved a couple issues we reported when giving feedback for the new `--check-cfg` feature [15] [16]. # `alloc` upgrade and reviewing As mentioned above, compiler upgrades will not update `alloc` anymore, since we are dropping our `alloc` fork [3]. Link: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1780-2024-05-02 [1] Link: https://rust-for-linux.com/rust-version-policy [2] Link: https://lore.kernel.org/rust-for-linux/20240328013603.206764-1-wedsonaf@gmail.com/ [3] Link: Rust-for-Linux#2 [4] Link: rust-lang/rust#120062 [5] Link: rust-lang/rust#120055 [6] Link: https://reviews.llvm.org/D86310 [7] Link: rust-lang/rust#117772 [8] Link: rust-lang/rust-clippy#10903 [9] Link: rust-lang/rust#119365 [10] Link: rust-lang/rust#119364 [11] Link: https://lore.kernel.org/rust-for-linux/ZWipTZysC2YL7qsq@Boquns-Mac-mini.home/ [12] Link: rust-lang/rust#120932 [13] Link: rust-lang/rust#120969 [14] Link: rust-lang/rust#121202 [15] Link: rust-lang/rust#121237 [16] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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Tracking Issue for asm_goto #119364

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Rust wanted features Rust-for-Linux/linux#354

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nbdd0121 added 7 commits February 24, 2024 18:49

Add asm label support to AST and HIR

93fa857

Add asm label support to THIR

040ab7d

Use slice.chain(option) for Successors

7152993

This makes more sense because most cases then second one is unwind target.

Change InlineAsm to allow multiple targets instead

b044aaa

Implement asm goto in MIR and MIR lowering

3b1dd1b

Add callbr support to LLVM wrapper

27e6ee1

Implement asm goto for LLVM and GCC backend

5e4fd6b

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Bless aarch64 asm test

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Rollup of 7 pull requests #122176

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Rollup of 8 pull requests #122182

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Rust unstable features needed for the kernel Rust-for-Linux/linux#2

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Add asm goto support to `asm!` #119365

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Add asm goto support to asm! #119365

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Add asm goto support to `asm!` #119365

Add asm goto support to `asm!` #119365