Strip out broken Emscripten unwinding code

Author: Jules-Bertholet

compiler/rustc_codegen_llvm/src/context.rs

@@ -99,7 +99,6 @@ pub struct CodegenCx<'ll, 'tcx> {
     pub dbg_cx: Option<debuginfo::CodegenUnitDebugContext<'ll, 'tcx>>,
 
     eh_personality: Cell<Option<&'ll Value>>,
-    eh_catch_typeinfo: Cell<Option<&'ll Value>>,
     pub rust_try_fn: Cell<Option<(&'ll Type, &'ll Value)>>,
 
     intrinsics: RefCell<FxHashMap<&'static str, (&'ll Type, &'ll Value)>>,
@@ -439,7 +438,6 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
             coverage_cx,
             dbg_cx,
             eh_personality: Cell::new(None),
-            eh_catch_typeinfo: Cell::new(None),
             rust_try_fn: Cell::new(None),
             intrinsics: Default::default(),
             local_gen_sym_counter: Cell::new(0),
@@ -889,25 +887,6 @@ impl<'ll> CodegenCx<'ll, '_> {
         }
         None
     }
-
-    pub(crate) fn eh_catch_typeinfo(&self) -> &'ll Value {
-        if let Some(eh_catch_typeinfo) = self.eh_catch_typeinfo.get() {
-            return eh_catch_typeinfo;
-        }
-        let tcx = self.tcx;
-        assert!(self.sess().target.is_like_emscripten);
-        let eh_catch_typeinfo = match tcx.lang_items().eh_catch_typeinfo() {
-            Some(def_id) => self.get_static(def_id),
-            _ => {
-                let ty = self
-                    .type_struct(&[self.type_ptr_to(self.type_isize()), self.type_i8p()], false);
-                self.declare_global("rust_eh_catch_typeinfo", ty)
-            }
-        };
-        let eh_catch_typeinfo = self.const_bitcast(eh_catch_typeinfo, self.type_i8p());
-        self.eh_catch_typeinfo.set(Some(eh_catch_typeinfo));
-        eh_catch_typeinfo
-    }
 }
 
 impl CodegenCx<'_, '_> {

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -431,8 +431,6 @@ fn try_intrinsic<'ll>(
         bx.store(bx.const_i32(0), dest, ret_align);
     } else if wants_msvc_seh(bx.sess()) {
         codegen_msvc_try(bx, try_func, data, catch_func, dest);
-    } else if bx.sess().target.is_like_emscripten {
-        codegen_emcc_try(bx, try_func, data, catch_func, dest);
     } else {
         codegen_gnu_try(bx, try_func, data, catch_func, dest);
     }
@@ -656,91 +654,6 @@ fn codegen_gnu_try<'ll>(
     bx.store(ret, dest, i32_align);
 }
 
-// Variant of codegen_gnu_try used for emscripten where Rust panics are
-// implemented using C++ exceptions. Here we use exceptions of a specific type
-// (`struct rust_panic`) to represent Rust panics.
-fn codegen_emcc_try<'ll>(
-    bx: &mut Builder<'_, 'll, '_>,
-    try_func: &'ll Value,
-    data: &'ll Value,
-    catch_func: &'ll Value,
-    dest: &'ll Value,
-) {
-    let (llty, llfn) = get_rust_try_fn(bx, &mut |mut bx| {
-        // Codegens the shims described above:
-        //
-        //   bx:
-        //      invoke %try_func(%data) normal %normal unwind %catch
-        //
-        //   normal:
-        //      ret 0
-        //
-        //   catch:
-        //      (%ptr, %selector) = landingpad
-        //      %rust_typeid = @llvm.eh.typeid.for(@_ZTI10rust_panic)
-        //      %is_rust_panic = %selector == %rust_typeid
-        //      %catch_data = alloca { i8*, i8 }
-        //      %catch_data[0] = %ptr
-        //      %catch_data[1] = %is_rust_panic
-        //      call %catch_func(%data, %catch_data)
-        //      ret 1
-        let then = bx.append_sibling_block("then");
-        let catch = bx.append_sibling_block("catch");
-
-        let try_func = llvm::get_param(bx.llfn(), 0);
-        let data = llvm::get_param(bx.llfn(), 1);
-        let catch_func = llvm::get_param(bx.llfn(), 2);
-        let try_func_ty = bx.type_func(&[bx.type_i8p()], bx.type_void());
-        bx.invoke(try_func_ty, try_func, &[data], then, catch, None);
-
-        bx.switch_to_block(then);
-        bx.ret(bx.const_i32(0));
-
-        // Type indicator for the exception being thrown.
-        //
-        // The first value in this tuple is a pointer to the exception object
-        // being thrown.  The second value is a "selector" indicating which of
-        // the landing pad clauses the exception's type had been matched to.
-        bx.switch_to_block(catch);
-        let tydesc = bx.eh_catch_typeinfo();
-        let lpad_ty = bx.type_struct(&[bx.type_i8p(), bx.type_i32()], false);
-        let vals = bx.landing_pad(lpad_ty, bx.eh_personality(), 2);
-        bx.add_clause(vals, tydesc);
-        bx.add_clause(vals, bx.const_null(bx.type_i8p()));
-        let ptr = bx.extract_value(vals, 0);
-        let selector = bx.extract_value(vals, 1);
-
-        // Check if the typeid we got is the one for a Rust panic.
-        let rust_typeid = bx.call_intrinsic("llvm.eh.typeid.for", &[tydesc]);
-        let is_rust_panic = bx.icmp(IntPredicate::IntEQ, selector, rust_typeid);
-        let is_rust_panic = bx.zext(is_rust_panic, bx.type_bool());
-
-        // We need to pass two values to catch_func (ptr and is_rust_panic), so
-        // create an alloca and pass a pointer to that.
-        let ptr_align = bx.tcx().data_layout.pointer_align.abi;
-        let i8_align = bx.tcx().data_layout.i8_align.abi;
-        let catch_data_type = bx.type_struct(&[bx.type_i8p(), bx.type_bool()], false);
-        let catch_data = bx.alloca(catch_data_type, ptr_align);
-        let catch_data_0 =
-            bx.inbounds_gep(catch_data_type, catch_data, &[bx.const_usize(0), bx.const_usize(0)]);
-        bx.store(ptr, catch_data_0, ptr_align);
-        let catch_data_1 =
-            bx.inbounds_gep(catch_data_type, catch_data, &[bx.const_usize(0), bx.const_usize(1)]);
-        bx.store(is_rust_panic, catch_data_1, i8_align);
-        let catch_data = bx.bitcast(catch_data, bx.type_i8p());
-
-        let catch_ty = bx.type_func(&[bx.type_i8p(), bx.type_i8p()], bx.type_void());
-        bx.call(catch_ty, catch_func, &[data, catch_data], None);
-        bx.ret(bx.const_i32(1));
-    });
-
-    // Note that no invoke is used here because by definition this function
-    // can't panic (that's what it's catching).
-    let ret = bx.call(llty, llfn, &[try_func, data, catch_func], None);
-    let i32_align = bx.tcx().data_layout.i32_align.abi;
-    bx.store(ret, dest, i32_align);
-}
-
 // Helper function to give a Block to a closure to codegen a shim function.
 // This is currently primarily used for the `try` intrinsic functions above.
 fn gen_fn<'ll, 'tcx>(

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -21,7 +21,7 @@ use rustc_span::symbol::Symbol;
 use rustc_span::DebuggerVisualizerFile;
 use rustc_target::spec::crt_objects::{CrtObjects, CrtObjectsFallback};
 use rustc_target::spec::{LinkOutputKind, LinkerFlavor, LldFlavor, SplitDebuginfo};
-use rustc_target::spec::{PanicStrategy, RelocModel, RelroLevel, SanitizerSet, Target};
+use rustc_target::spec::{RelocModel, RelroLevel, SanitizerSet, Target};
 
 use super::archive::{find_library, ArchiveBuilder};
 use super::command::Command;
@@ -2047,15 +2047,6 @@ fn add_order_independent_options(
         cmd.no_crt_objects();
     }
 
-    if sess.target.is_like_emscripten {
-        cmd.arg("-s");
-        cmd.arg(if sess.panic_strategy() == PanicStrategy::Abort {
-            "DISABLE_EXCEPTION_CATCHING=1"
-        } else {
-            "DISABLE_EXCEPTION_CATCHING=0"
-        });
-    }
-
     if flavor == LinkerFlavor::PtxLinker {
         // Provide the linker with fallback to internal `target-cpu`.
         cmd.arg("--fallback-arch");

compiler/rustc_hir/src/lang_items.rs

@@ -270,7 +270,6 @@ language_item_table! {
     Start,                   sym::start,               start_fn,                   Target::Fn,             GenericRequirement::Exact(1);
 
     EhPersonality,           sym::eh_personality,      eh_personality,             Target::Fn,             GenericRequirement::None;
-    EhCatchTypeinfo,         sym::eh_catch_typeinfo,   eh_catch_typeinfo,          Target::Static,         GenericRequirement::None;
 
     OwnedBox,                sym::owned_box,           owned_box,                  Target::Struct,         GenericRequirement::Minimum(1);
 

compiler/rustc_hir/src/weak_lang_items.rs

@@ -42,6 +42,5 @@ impl LanguageItems {
 weak_lang_items! {
     panic_impl,         PanicImpl,          rust_begin_unwind;
     eh_personality,     EhPersonality,      rust_eh_personality;
-    eh_catch_typeinfo,  EhCatchTypeinfo,    rust_eh_catch_typeinfo;
     oom,                Oom,                rust_oom;
 }

compiler/rustc_middle/src/middle/lang_items.rs

@@ -53,9 +53,7 @@ pub fn required(tcx: TyCtxt<'_>, lang_item: LangItem) -> bool {
     // symbols. Other panic runtimes ensure that the relevant symbols are
     // available to link things together, but they're never exercised.
     match tcx.sess.panic_strategy() {
-        PanicStrategy::Abort => {
-            lang_item != LangItem::EhPersonality && lang_item != LangItem::EhCatchTypeinfo
-        }
+        PanicStrategy::Abort => lang_item != LangItem::EhPersonality,
         PanicStrategy::Unwind => true,
     }
 }

compiler/rustc_passes/src/weak_lang_items.rs

@@ -17,9 +17,6 @@ pub fn check_crate<'tcx>(tcx: TyCtxt<'tcx>, items: &mut lang_items::LanguageItem
     if items.eh_personality().is_none() {
         items.missing.push(LangItem::EhPersonality);
     }
-    if tcx.sess.target.is_like_emscripten && items.eh_catch_typeinfo().is_none() {
-        items.missing.push(LangItem::EhCatchTypeinfo);
-    }
 
     let crate_items = tcx.hir_crate_items(());
     for id in crate_items.foreign_items() {

compiler/rustc_span/src/symbol.rs

@@ -619,7 +619,6 @@ symbols! {
         e,
         edition_macro_pats,
         edition_panic,
-        eh_catch_typeinfo,
         eh_personality,
         emit_enum,
         emit_enum_variant,
@@ -1164,7 +1163,6 @@ symbols! {
         rust_2024_preview,
         rust_begin_unwind,
         rust_cold_cc,
-        rust_eh_catch_typeinfo,
         rust_eh_personality,
         rust_eh_register_frames,
         rust_eh_unregister_frames,

compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs

@@ -22,9 +22,12 @@ pub fn target() -> Target {
             "-s".into(),
             "ASSERTIONS=1".into(),
             "-s".into(),
+            "DISABLE_EXCEPTION_THROWING=1".into(),
+            "-s".into(),
             "DISABLE_EXCEPTION_CATCHING=1".into(),
             "-s".into(),
             "ABORTING_MALLOC=0".into(),
+            "-fno-exceptions".into(),
             "-Wl,--fatal-warnings".into(),
         ],
     );

library/panic_abort/src/lib.rs

@@ -134,17 +134,6 @@ pub mod personalities {
         1 // `ExceptionContinueSearch`
     }
 
-    // Similar to above, this corresponds to the `eh_catch_typeinfo` lang item
-    // that's only used on Emscripten currently.
-    //
-    // Since panics don't generate exceptions and foreign exceptions are
-    // currently UB with -C panic=abort (although this may be subject to
-    // change), any catch_unwind calls will never use this typeinfo.
-    #[rustc_std_internal_symbol]
-    #[allow(non_upper_case_globals)]
-    #[cfg(target_os = "emscripten")]
-    static rust_eh_catch_typeinfo: [usize; 2] = [0; 2];
-
     // These two are called by our startup objects on i686-pc-windows-gnu, but
     // they don't need to do anything so the bodies are nops.
     #[rustc_std_internal_symbol]