From 10e053dbb5c7ac3679044f222112682c9fc0758a Mon Sep 17 00:00:00 2001
From: Hood Chatham <roberthoodchatham@gmail.com>
Date: Mon, 26 Jan 2026 10:34:50 -0800
Subject: [PATCH] Implement `set_output_kind` for Emscripten linker

This makes cdylibs compile to working Emscripten dynamic libraries without passing extra
RUSTFLAGS. This was previously approved as PR 98358 but there were CI failures that I
never got around to fixing.
---
 compiler/rustc_codegen_ssa/src/back/linker.rs     | 15 ++++++++++++++-
 .../src/spec/targets/wasm32_unknown_emscripten.rs |  2 ++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index 1b75db51140b..db49f92e39ac 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -1208,10 +1208,23 @@ impl<'a> Linker for EmLinker<'a> {
 
     fn set_output_kind(
         &mut self,
-        _output_kind: LinkOutputKind,
+        output_kind: LinkOutputKind,
         _crate_type: CrateType,
         _out_filename: &Path,
     ) {
+        match output_kind {
+            LinkOutputKind::DynamicNoPicExe | LinkOutputKind::DynamicPicExe => {
+                self.cmd.arg("-sMAIN_MODULE=2");
+            }
+            LinkOutputKind::DynamicDylib | LinkOutputKind::StaticDylib => {
+                self.cmd.arg("-sSIDE_MODULE=2");
+            }
+            // -fno-pie is the default on Emscripten.
+            LinkOutputKind::StaticNoPicExe | LinkOutputKind::StaticPicExe => {}
+            LinkOutputKind::WasiReactorExe => {
+                unreachable!();
+            }
+        }
     }
 
     fn link_dylib_by_name(&mut self, name: &str, _verbatim: bool, _as_needed: bool) {
diff --git a/compiler/rustc_target/src/spec/targets/wasm32_unknown_emscripten.rs b/compiler/rustc_target/src/spec/targets/wasm32_unknown_emscripten.rs
index 47623c34dce3..fb735b54dd82 100644
--- a/compiler/rustc_target/src/spec/targets/wasm32_unknown_emscripten.rs
+++ b/compiler/rustc_target/src/spec/targets/wasm32_unknown_emscripten.rs
@@ -19,6 +19,8 @@ pub(crate) fn target() -> Target {
         pre_link_args,
         post_link_args,
         relocation_model: RelocModel::Pic,
+        crt_static_respected: true,
+        crt_static_default: true,
         panic_strategy: PanicStrategy::Unwind,
         no_default_libraries: false,
         families: cvs!["unix", "wasm"],