std support for wasm32 panic=unwind by coolreader18 · Pull Request #121438 · rust-lang/rust (original) (raw)

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Tracking issue: #118168

This adds std support for -Cpanic=unwind on wasm, and with it slightly more fleshed out rustc support. Now, the stable default is still panic=abort without exception-handling, but if you -Zbuild-std with RUSTFLAGS=-Cpanic=unwind, you get wasm exception-handling try/catch blocks in the binary:

#[no_mangle] pub fn foo_bar(x: bool) -> *mut u8 { let s = Box::::from("hello"); maybe_panic(x); Box::into_raw(s).cast() }

#[inline(never)] #[no_mangle] fn maybe_panic(x: bool) { if x { panic!("AAAAA"); } }

;; snip... (try labellabellabel5 (do (call $maybe_panic (local.get $0) ) (br labellabellabel1) ) (catch_all (global.set $__stack_pointer (local.get $1) ) (call $__rust_dealloc (local.get $2) (i32.const 5) (i32.const 1) ) (rethrow labellabellabel5) ) ) ;; snip...

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rustbot added S-waiting-on-review

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Feb 22, 2024

Also, though this is more of a future concern, idk if a panic=unwind std would be able to run nicely in a panic=abort binary atm - if the user is trying to keep backwards compatibility to wasm MVP, llvm or something would have to strip the try instructions from the end result.

extern "C" {
/// LLVM lowers this intrinsic to the `throw` instruction.
#[link_name = "llvm.wasm.throw"]
fn wasm_throw(tag: i32, ptr: *mut u8) -> !;

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Maybe add a new rust intrinsic which lowers to this LLVM intrinsic when using the LLVM backend?

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I think I wanna put it in stdarch, alongside the other wasm instructions. A full extern "rust-intrinsic" intrinsic shouldn't be necessary.

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rustbot added the T-bootstrap

Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap)

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Feb 22, 2024

This PR changes how LLVM is built. Consider updating src/bootstrap/download-ci-llvm-stamp.

Ok, now wasi uses libunwind, while -unknown still uses wasm.throw directly. It does seem like the scheme that LLVM implements is a tooling convention (so, not just LLVM's specific implementation) but it does say it's for C++ specifically, and says other languages should have distinct tags. However, doing that means (unless I'm reading the exception-handling proposal wrong) that exceptions caught in a different language can't be cleaned up. But maybe that's fine, for now.

Oh, actually, if we had a distinct tag for panics it would just mean that a C++ exception would skip catch_unwind. Which is fine, if I'm reading the C-unwind rfc correctly.

As noted in the summary, if a Rust frame containing a pending catch_unwind call is unwound by a foreign exception, the behavior is undefined for now.

If we really want to process a C++ exception with catch_unwind in the future, we could just implement the itanium wasm EH scheme in library/unwind and codegen a catch $cpp_exc_tag for r#try. Once llvm supports that.

Actually, knowing that, do you think wasi even needs llvm's libunwind? We can handle it just fine ourselves, obviously, and it will indeed cause UB at catch_unwind, but that's fine, and that'll be fixable if we want to once LLVM lets you specify other tags.

I've convinced myself I think, lol

This was referenced

Feb 28, 2024

I'm not clear, is this waiting on the stdarch change, or vice versa?

Vice versa - the stdarch PR will fail until this is in nightly.

📌 Commit c7fcf43 has been approved by cuviper

It is now in the queue for this repository.

bors added the S-waiting-on-bors

Status: Waiting on bors to run and complete tests. Bors will change the label on completion.

label

Mar 4, 2024

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request

Mar 5, 2024

…r=cuviper

std support for wasm32 panic=unwind

Tracking issue: rust-lang#118168

#[no_mangle]
pub fn foo_bar(x: bool) -> *mut u8 {
    let s = Box::<str>::from("hello");
    maybe_panic(x);
    Box::into_raw(s).cast()
}

#[inline(never)]
#[no_mangle]
fn maybe_panic(x: bool) {
    if x {
        panic!("AAAAA");
    }
}

;; snip...
(try <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>a</mi><mi>b</mi><mi>e</mi><mi>l</mi></mrow><annotation encoding="application/x-tex">label</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">ab</span><span class="mord mathnormal">e</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span></span></span></span>5
 (do
  (call $maybe_panic
   (local.get $0)
  )
  (br <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>a</mi><mi>b</mi><mi>e</mi><mi>l</mi></mrow><annotation encoding="application/x-tex">label</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">ab</span><span class="mord mathnormal">e</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span></span></span></span>1)
 )
 (catch_all
  (global.set $__stack_pointer
   (local.get $1)
  )
  (call $__rust_dealloc
   (local.get $2)
   (i32.const 5)
   (i32.const 1)
  )
  (rethrow <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>a</mi><mi>b</mi><mi>e</mi><mi>l</mi></mrow><annotation encoding="application/x-tex">label</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">ab</span><span class="mord mathnormal">e</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span></span></span></span>5)
 )
)
;; snip...

bors added a commit to rust-lang-ci/rust that referenced this pull request

Mar 5, 2024

This was referenced

Mar 11, 2024

bors added a commit to rust-lang-ci/rust that referenced this pull request

Mar 11, 2024

…kingjubilee

Rollup of 15 pull requests

Successful merges:

rust-lang#116791 (Allow codegen backends to opt-out of parallel codegen)
rust-lang#116793 (Allow targets to override default codegen backend)
rust-lang#117458 (LLVM Bitcode Linker: A self contained linker for nvptx and other targets)
rust-lang#119385 (Fix type resolution of associated const equality bounds (take 2))
rust-lang#121438 (std support for wasm32 panic=unwind)
rust-lang#121893 (Add tests (and a bit of cleanup) for interior mut handling in promotion and const-checking)
rust-lang#122080 (Clarity improvements to DropTree)
rust-lang#122152 (Improve diagnostics for parenthesized type arguments)
rust-lang#122166 (Remove the unused field_remapping field from TypeLowering)
rust-lang#122249 (interpret: do not call machine read hooks during validation)
rust-lang#122299 (Store backtrace for must_produce_diag)
rust-lang#122318 (Revision-related tweaks for next-solver tests)
rust-lang#122320 (Use ptradd for vtable indexing)
rust-lang#122328 (unix_sigpipe: Replace inherit with sig_dfl in syntax tests)
rust-lang#122330 (bootstrap readme: fix, improve, update)

r? @ghost @rustbot modify labels: rollup

rust-timer added a commit to rust-lang-ci/rust that referenced this pull request

Mar 11, 2024

Rollup merge of rust-lang#121438 - coolreader18:wasm32-panic-unwind, r=cuviper

std support for wasm32 panic=unwind

Tracking issue: rust-lang#118168

#[no_mangle]
pub fn foo_bar(x: bool) -> *mut u8 {
    let s = Box::<str>::from("hello");
    maybe_panic(x);
    Box::into_raw(s).cast()
}

#[inline(never)]
#[no_mangle]
fn maybe_panic(x: bool) {
    if x {
        panic!("AAAAA");
    }
}

;; snip...
(try <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>a</mi><mi>b</mi><mi>e</mi><mi>l</mi></mrow><annotation encoding="application/x-tex">label</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">ab</span><span class="mord mathnormal">e</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span></span></span></span>5
 (do
  (call $maybe_panic
   (local.get $0)
  )
  (br <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>a</mi><mi>b</mi><mi>e</mi><mi>l</mi></mrow><annotation encoding="application/x-tex">label</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">ab</span><span class="mord mathnormal">e</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span></span></span></span>1)
 )
 (catch_all
  (global.set $__stack_pointer
   (local.get $1)
  )
  (call $__rust_dealloc
   (local.get $2)
   (i32.const 5)
   (i32.const 1)
  )
  (rethrow <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>a</mi><mi>b</mi><mi>e</mi><mi>l</mi></mrow><annotation encoding="application/x-tex">label</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">ab</span><span class="mord mathnormal">e</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span></span></span></span>5)
 )
)
;; snip...

tgross35 added a commit to tgross35/rust that referenced this pull request

Oct 12, 2024

… r=bjorn3

Use throw intrinsic from stdarch in wasm libunwind

Tracking issue: rust-lang#118168

This is a very belated followup to rust-lang#121438; now that rust-lang/stdarch#1542 is merged, we can use the intrinsic exported from core::arch instead of defining it inline. I also cleaned up the cfgs a bit and added a more detailed comment.

tgross35 added a commit to tgross35/rust that referenced this pull request

Oct 13, 2024

… r=bjorn3

Use throw intrinsic from stdarch in wasm libunwind

Tracking issue: rust-lang#118168

rust-timer added a commit to rust-lang-ci/rust that referenced this pull request

Oct 13, 2024

Rollup merge of rust-lang#131418 - coolreader18:wasm-exc-use-stdarch, r=bjorn3

Use throw intrinsic from stdarch in wasm libunwind

Tracking issue: rust-lang#118168

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