From 7c8be3d3816d10c992a5cc0998b1912a1a167155 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E7=8E=8B=E5=AE=87=E9=80=B8?= <Strawberry_Str@hotmail.com>
Date: Tue, 20 May 2025 14:38:55 +0800
Subject: [PATCH] Don't reload proc macros on fork

---
 compiler/rustc_metadata/Cargo.toml     | 2 +-
 compiler/rustc_metadata/src/creader.rs | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_metadata/Cargo.toml b/compiler/rustc_metadata/Cargo.toml
index cfe412e99d8d5..451b231fed54e 100644
--- a/compiler/rustc_metadata/Cargo.toml
+++ b/compiler/rustc_metadata/Cargo.toml
@@ -31,7 +31,7 @@ tempfile = "3.7.1"
 tracing = "0.1"
 # tidy-alphabetical-end
 
-[target.'cfg(target_os = "aix")'.dependencies]
+[target.'cfg(any(target_os = "aix", target_os = "cygwin"))'.dependencies]
 # tidy-alphabetical-start
 libc = "0.2"
 # tidy-alphabetical-end
diff --git a/compiler/rustc_metadata/src/creader.rs b/compiler/rustc_metadata/src/creader.rs
index 07fb2de8a3e0c..4d12c73d0dd07 100644
--- a/compiler/rustc_metadata/src/creader.rs
+++ b/compiler/rustc_metadata/src/creader.rs
@@ -1442,6 +1442,11 @@ fn load_dylib(path: &Path, max_attempts: usize) -> Result<libloading::Library, S
                         attempt + 1
                     );
                 }
+                #[cfg(target_os = "cygwin")]
+                unsafe {
+                    // We don't need to reload proc macros in child processes.
+                    libc::dlfork(libc::FORK_NO_RELOAD);
+                }
                 return Ok(lib);
             }
             Err(err) => {