Rollup merge of #131830 - hoodmane:emscripten-wasm-eh, r=workingjubilee

Add support for wasm exception handling to Emscripten target

This is a draft because we need some additional setting for the Emscripten target to select between the old exception handling and the new exception handling. I don't know how to add a setting like that, would appreciate advice from Rust folks. We could maybe choose to use the new exception handling if `Ctarget-feature=+exception-handling` is passed? I tried this but I get errors from llvm so I'm not doing it right.

Author: jhpratt

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -109,7 +109,10 @@ unsafe fn configure_llvm(sess: &Session) {
             add("-wasm-enable-eh", false);
         }
 
-        if sess.target.os == "emscripten" && sess.panic_strategy() == PanicStrategy::Unwind {
+        if sess.target.os == "emscripten"
+            && !sess.opts.unstable_opts.emscripten_wasm_eh
+            && sess.panic_strategy() == PanicStrategy::Unwind
+        {
             add("-enable-emscripten-cxx-exceptions", false);
         }
 

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -2451,10 +2451,12 @@ fn add_order_independent_options(
     }
 
     if sess.target.os == "emscripten" {
-        cmd.cc_arg("-s").cc_arg(if sess.panic_strategy() == PanicStrategy::Abort {
-            "DISABLE_EXCEPTION_CATCHING=1"
+        cmd.cc_arg(if sess.panic_strategy() == PanicStrategy::Abort {
+            "-sDISABLE_EXCEPTION_CATCHING=1"
+        } else if sess.opts.unstable_opts.emscripten_wasm_eh {
+            "-fwasm-exceptions"
         } else {
-            "DISABLE_EXCEPTION_CATCHING=0"
+            "-sDISABLE_EXCEPTION_CATCHING=0"
         });
     }
 

compiler/rustc_codegen_ssa/src/base.rs

@@ -388,7 +388,8 @@ pub(crate) fn build_shift_expr_rhs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 // exceptions. This means that the VM does the unwinding for
 // us
 pub fn wants_wasm_eh(sess: &Session) -> bool {
-    sess.target.is_like_wasm && sess.target.os != "emscripten"
+    sess.target.is_like_wasm
+        && (sess.target.os != "emscripten" || sess.opts.unstable_opts.emscripten_wasm_eh)
 }
 
 /// Returns `true` if this session's target will use SEH-based unwinding.

compiler/rustc_feature/src/builtin_attrs.rs

@@ -37,6 +37,7 @@ const GATED_CFGS: &[GatedCfg] = &[
     (sym::sanitizer_cfi_normalize_integers, sym::cfg_sanitizer_cfi, Features::cfg_sanitizer_cfi),
     // this is consistent with naming of the compiler flag it's for
     (sym::fmt_debug, sym::fmt_debug, Features::fmt_debug),
+    (sym::emscripten_wasm_eh, sym::cfg_emscripten_wasm_eh, Features::cfg_emscripten_wasm_eh),
 ];
 
 /// Find a gated cfg determined by the `pred`icate which is given the cfg's name.

compiler/rustc_feature/src/unstable.rs

@@ -202,6 +202,8 @@ declare_features! (
     (internal, allow_internal_unstable, "1.0.0", None),
     /// Allows using anonymous lifetimes in argument-position impl-trait.
     (unstable, anonymous_lifetime_in_impl_trait, "1.63.0", None),
+    /// Allows access to the emscripten_wasm_eh config, used by panic_unwind and unwind
+    (internal, cfg_emscripten_wasm_eh, "CURRENT_RUSTC_VERSION", None),
     /// Allows identifying the `compiler_builtins` crate.
     (internal, compiler_builtins, "1.13.0", None),
     /// Allows writing custom MIR

compiler/rustc_interface/src/tests.rs

@@ -782,6 +782,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(dwarf_version, Some(5));
     tracked!(embed_source, true);
     tracked!(emit_thin_lto, false);
+    tracked!(emscripten_wasm_eh, true);
     tracked!(export_executable_symbols, true);
     tracked!(fewer_names, Some(true));
     tracked!(fixed_x18, true);

compiler/rustc_passes/src/weak_lang_items.rs

@@ -26,7 +26,10 @@ pub(crate) fn check_crate(
     if items.eh_personality().is_none() {
         items.missing.push(LangItem::EhPersonality);
     }
-    if tcx.sess.target.os == "emscripten" && items.eh_catch_typeinfo().is_none() {
+    if tcx.sess.target.os == "emscripten"
+        && items.eh_catch_typeinfo().is_none()
+        && !tcx.sess.opts.unstable_opts.emscripten_wasm_eh
+    {
         items.missing.push(LangItem::EhCatchTypeinfo);
     }
 

compiler/rustc_session/src/config/cfg.rs

@@ -143,6 +143,7 @@ pub(crate) fn disallow_cfgs(sess: &Session, user_cfgs: &Cfg) {
             | (sym::target_has_atomic_load_store, Some(_))
             | (sym::target_thread_local, None) => disallow(cfg, "--target"),
             (sym::fmt_debug, None | Some(_)) => disallow(cfg, "-Z fmt-debug"),
+            (sym::emscripten_wasm_eh, None | Some(_)) => disallow(cfg, "-Z emscripten_wasm_eh"),
             _ => {}
         }
     }
@@ -295,6 +296,10 @@ pub(crate) fn default_configuration(sess: &Session) -> Cfg {
         ins_none!(sym::ub_checks);
     }
 
+    // Nightly-only implementation detail for the `panic_unwind` and `unwind` crates.
+    if sess.is_nightly_build() && sess.opts.unstable_opts.emscripten_wasm_eh {
+        ins_none!(sym::emscripten_wasm_eh);
+    }
     ret
 }
 

compiler/rustc_session/src/options.rs

@@ -1771,6 +1771,8 @@ options! {
         "emit a section containing stack size metadata (default: no)"),
     emit_thin_lto: bool = (true, parse_bool, [TRACKED],
         "emit the bc module with thin LTO info (default: yes)"),
+    emscripten_wasm_eh: bool = (false, parse_bool, [TRACKED],
+        "Use WebAssembly error handling for wasm32-unknown-emscripten"),
     enforce_type_length_limit: bool = (false, parse_bool, [TRACKED],
         "enforce the type length limit when monomorphizing instances in codegen"),
     export_executable_symbols: bool = (false, parse_bool, [TRACKED],

compiler/rustc_span/src/symbol.rs

@@ -570,6 +570,7 @@ symbols! {
         cfg_autodiff_fallback,
         cfg_boolean_literals,
         cfg_doctest,
+        cfg_emscripten_wasm_eh,
         cfg_eval,
         cfg_fmt_debug,
         cfg_hide,
@@ -823,6 +824,7 @@ symbols! {
         emit_enum_variant_arg,
         emit_struct,
         emit_struct_field,
+        emscripten_wasm_eh,
         enable,
         encode,
         end,