Rollup merge of rust-lang#65832 - tlively:emscripten-exception-handling, r=alexcrichton

Re-enable Emscripten's exception handling support

Passes LLVM codegen and Emscripten link-time flags for exception
handling if and only if the panic strategy is `unwind`. Sets the
default panic strategy for Emscripten targets to `unwind`. Re-enables
tests that depend on unwinding support for Emscripten, including
`should_panic` tests.

r? @alexcrichton

Author: tmandry

src/bootstrap/native.rs

@@ -534,6 +534,10 @@ impl Step for TestHelpers {
         builder.info("Building test helpers");
         t!(fs::create_dir_all(&dst));
         let mut cfg = cc::Build::new();
+        // FIXME: Workaround for https://github.com/emscripten-core/emscripten/issues/9013
+        if target.contains("emscripten") {
+            cfg.pic(false);
+        }
 
         // We may have found various cross-compilers a little differently due to our
         // extra configuration, so inform gcc of these compilers. Note, though, that

src/librustc_codegen_llvm/llvm_util.rs

@@ -3,7 +3,7 @@ use crate::llvm;
 use syntax_pos::symbol::Symbol;
 use rustc::session::Session;
 use rustc::session::config::PrintRequest;
-use rustc_target::spec::MergeFunctions;
+use rustc_target::spec::{MergeFunctions, PanicStrategy};
 use libc::c_int;
 use std::ffi::CString;
 use syntax::feature_gate::UnstableFeatures;
@@ -73,6 +73,11 @@ unsafe fn configure_llvm(sess: &Session) {
             }
         }
 
+        if sess.target.target.target_os == "emscripten" &&
+            sess.panic_strategy() == PanicStrategy::Unwind {
+            add("-enable-emscripten-cxx-exceptions");
+        }
+
         // HACK(eddyb) LLVM inserts `llvm.assume` calls to preserve align attributes
         // during inlining. Unfortunately these may block other optimizations.
         add("-preserve-alignment-assumptions-during-inlining=false");

src/librustc_codegen_ssa/back/symbol_export.rs

@@ -364,8 +364,9 @@ fn symbol_export_level(tcx: TyCtxt<'_>, sym_def_id: DefId) -> SymbolExportLevel
         codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
 
     if is_extern && !std_internal {
-        // Emscripten cannot export statics, so reduce their export level here
-        if tcx.sess.target.target.options.is_like_emscripten {
+        let target = &tcx.sess.target.target.llvm_target;
+        // WebAssembly cannot export data symbols, so reduce their export level
+        if target.contains("wasm32") || target.contains("emscripten") {
             if let Some(Node::Item(&hir::Item {
                 kind: hir::ItemKind::Static(..),
                 ..

src/librustc_target/spec/wasm32_unknown_emscripten.rs

@@ -9,12 +9,8 @@ pub fn target() -> Result<Target, String> {
                                "-s".to_string(),
                                "ASSERTIONS=1".to_string(),
                                "-s".to_string(),
-                               "DISABLE_EXCEPTION_CATCHING=1".to_string(),
-                               "-s".to_string(),
                                "ABORTING_MALLOC=0".to_string(),
-                               // FIXME(tlively): Enable this linker option once libc type errors
-                               // are resolved. See https://github.com/rust-lang/libc/pull/1478.
-                               // "-Wl,--fatal-warnings".to_string(),
+                               "-Wl,--fatal-warnings".to_string(),
                                ]);
 
     let opts = TargetOptions {
@@ -24,10 +20,7 @@ pub fn target() -> Result<Target, String> {
         linker: None,
         linker_is_gnu: true,
         is_like_emscripten: true,
-        // FIXME(tlively): Emscripten supports unwinding, but we would have to pass
-        // -enable-emscripten-cxx-exceptions to LLVM at codegen time and merge
-        // https://reviews.llvm.org/rG5c3cdef84b82464756bb571c13c31cf7773860c3to use it.
-        panic_strategy: PanicStrategy::Abort,
+        panic_strategy: PanicStrategy::Unwind,
         post_link_args,
         target_family: Some("unix".to_string()),
         .. wasm32_base::options()

src/libtest/lib.rs

@@ -441,9 +441,9 @@ pub fn run_test(
 ) {
     let TestDescAndFn { desc, testfn } = test;
 
-    // FIXME: Re-enable emscripten once it can catch panics again
+    // Emscripten can catch panics but other wasm targets cannot
     let ignore_because_no_process_support = desc.should_panic != ShouldPanic::No
-        && (cfg!(target_arch = "wasm32") || cfg!(target_os = "emscripten"));
+        && cfg!(target_arch = "wasm32") && !cfg!(target_os = "emscripten");
 
     if force_ignore || desc.ignore || ignore_because_no_process_support {
         let message = CompletedTest::new(desc, TrIgnored, None, Vec::new());

src/test/codegen/c-variadic.rs

@@ -1,4 +1,4 @@
-// ignore-emscripten compiled with panic=abort by default
+// ignore-wasm32-bare compiled with panic=abort by default
 // compile-flags: -C no-prepopulate-passes
 // ignore-tidy-linelength
 

src/test/codegen/drop.rs

@@ -1,4 +1,4 @@
-// ignore-emscripten compiled with panic=abort by default
+// ignore-wasm32-bare compiled with panic=abort by default
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]

src/test/codegen/personality_lifetimes.rs

@@ -1,5 +1,5 @@
 // ignore-msvc
-// ignore-emscripten compiled with panic=abort by default
+// ignore-wasm32-bare compiled with panic=abort by default
 
 // compile-flags: -O -C no-prepopulate-passes
 

src/test/codegen/unwind-extern-exports.rs

@@ -1,5 +1,5 @@
 // compile-flags: -C opt-level=0
-// ignore-emscripten compiled with panic=abort by default
+// ignore-wasm32-bare compiled with panic=abort by default
 
 #![crate_type = "lib"]
 #![feature(unwind_attributes)]

src/test/codegen/unwind-extern-imports.rs

@@ -1,5 +1,5 @@
 // compile-flags: -C no-prepopulate-passes
-// ignore-emscripten compiled with panic=abort by default
+// ignore-wasm32-bare compiled with panic=abort by default
 
 #![crate_type = "lib"]
 #![feature(unwind_attributes)]