From 2fa2746aca02b97ce49e72ac529c16d709cee92f Mon Sep 17 00:00:00 2001
From: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Date: Mon, 22 Jun 2026 12:01:34 +0200
Subject: [PATCH] Fix linking for wasm with crate metadata included

On wasm the crate metadata ends up in a custom section. It is not
possible to refer to create symbols inside a custom section, so
attempting to export it during linking will result in a linker error.
This keeps the target spec flag to deny compiling rust dylibs for wasm,
but may theoretically allow compiling wasm rust dylibs with a custom
target spec. It will help with wasm proc-macros. And in the future we
can try to flip the only-cdylib option to false on wasm.
---
 compiler/rustc_codegen_ssa/src/back/linker.rs | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index bde285c5c18fd..4041bfaa24cf0 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -1817,7 +1817,13 @@ pub(crate) fn exported_symbols(
         exported_symbols_for_non_proc_macro(tcx, crate_type)
     };
 
-    if crate_type == CrateType::Dylib || crate_type == CrateType::ProcMacro {
+    // Preserve the metadata symbol to ensure the metadata section doesn't get removed by the
+    // linker. On wasm however the metadata is put in a custom section, to which symbols can't
+    // refer, so there is no metadata symbol there. Luckily custom sections are always preserved by
+    // the linker.
+    if (crate_type == CrateType::Dylib || crate_type == CrateType::ProcMacro)
+        && !tcx.sess.target.is_like_wasm
+    {
         let metadata_symbol_name = exported_symbols::metadata_symbol_name(tcx);
         symbols.push((metadata_symbol_name, SymbolExportKind::Data));
     }