From 9abcfa55c31881a3f72becd5bca9504b46c3ed8f Mon Sep 17 00:00:00 2001
From: Dan Gohman <dev@sunfishcode.online>
Date: Thu, 21 Jan 2021 15:58:50 -0800
Subject: [PATCH] Don't link with --export-dynamic on wasm32-wasi

Remove --export-dynamic from the link arguments on the wasm32-wasi
target, as it emits spurious exports and increases code size.

Leave it in place for wasm32-unknown-unknown and
wasm32-unknown-emscripten. Even though it isn't a great solution
there, users are likely depending on its behavior there.
---
 compiler/rustc_target/src/spec/wasm32_base.rs   |  9 ---------
 .../src/spec/wasm32_unknown_emscripten.rs       | 13 ++++++++++++-
 .../src/spec/wasm32_unknown_unknown.rs          | 17 ++++++++++++-----
 3 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/compiler/rustc_target/src/spec/wasm32_base.rs b/compiler/rustc_target/src/spec/wasm32_base.rs
index a7957d84cbe..bfef3d37228 100644
--- a/compiler/rustc_target/src/spec/wasm32_base.rs
+++ b/compiler/rustc_target/src/spec/wasm32_base.rs
@@ -55,15 +55,6 @@ pub fn options() -> TargetOptions {
     // to do so.
     arg("--no-demangle");
 
-    // The symbol visibility story is a bit in flux right now with LLD.
-    // It's... not entirely clear to me what's going on, but this looks to
-    // make everything work when `export_symbols` isn't otherwise called for
-    // things like executables.
-    //
-    // This is really only here to get things working. If it can be removed and
-    // basic tests still work, then sounds like it should be removed!
-    arg("--export-dynamic");
-
     let mut pre_link_args = BTreeMap::new();
     pre_link_args.insert(LinkerFlavor::Lld(LldFlavor::Wasm), lld_args);
     pre_link_args.insert(LinkerFlavor::Gcc, clang_args);
diff --git a/compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs b/compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs
index c12757b8f98..9f69ce16c21 100644
--- a/compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs
+++ b/compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs
@@ -2,6 +2,17 @@ use super::wasm32_base;
 use super::{LinkArgs, LinkerFlavor, PanicStrategy, Target, TargetOptions};
 
 pub fn target() -> Target {
+    let mut options = wasm32_base::options();
+
+    let clang_args = options.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap();
+
+    // Rust really needs a way for users to specify exports and imports in
+    // the source code. --export-dynamic isn't the right tool for this job,
+    // however it does have the side effect of automatically exporting a lot
+    // of symbols, which approximates what people want when compiling for
+    // wasm32-unknown-unknown expect, so use it for now.
+    clang_args.push("--export-dynamic".to_string());
+
     let mut post_link_args = LinkArgs::new();
     post_link_args.insert(
         LinkerFlavor::Em,
@@ -28,7 +39,7 @@ pub fn target() -> Target {
         panic_strategy: PanicStrategy::Unwind,
         post_link_args,
         os_family: Some("unix".to_string()),
-        ..wasm32_base::options()
+        ..options
     };
     Target {
         llvm_target: "wasm32-unknown-emscripten".to_string(),
diff --git a/compiler/rustc_target/src/spec/wasm32_unknown_unknown.rs b/compiler/rustc_target/src/spec/wasm32_unknown_unknown.rs
index 6037aa5b430..5e89ba2520b 100644
--- a/compiler/rustc_target/src/spec/wasm32_unknown_unknown.rs
+++ b/compiler/rustc_target/src/spec/wasm32_unknown_unknown.rs
@@ -26,11 +26,18 @@ pub fn target() -> Target {
     // For now this target just never has an entry symbol no matter the output
     // type, so unconditionally pass this.
     clang_args.push("-Wl,--no-entry".to_string());
-    options
-        .pre_link_args
-        .get_mut(&LinkerFlavor::Lld(LldFlavor::Wasm))
-        .unwrap()
-        .push("--no-entry".to_string());
+
+    // Rust really needs a way for users to specify exports and imports in
+    // the source code. --export-dynamic isn't the right tool for this job,
+    // however it does have the side effect of automatically exporting a lot
+    // of symbols, which approximates what people want when compiling for
+    // wasm32-unknown-unknown expect, so use it for now.
+    clang_args.push("-Wl,--export-dynamic".to_string());
+
+    // Add the flags to wasm-ld's args too.
+    let lld_args = options.pre_link_args.get_mut(&LinkerFlavor::Lld(LldFlavor::Wasm)).unwrap();
+    lld_args.push("--no-entry".to_string());
+    lld_args.push("--export-dynamic".to_string());
 
     Target {
         llvm_target: "wasm32-unknown-unknown".to_string(),