From baf0369b90d6cd171d1948a747211f38d3974bea Mon Sep 17 00:00:00 2001
From: Alexandre Zollinger Chohfi <alzollin@microsoft.com>
Date: Thu, 22 Oct 2026 10:53:32 -0700
Subject: [PATCH 1/2] perf(windows): delay-load system DLLs the proxies don't
 use

Add user32, shell32, ole32, oleaut32, crypt32, secur32 and ws2_32 to the existing delay-load list for rustup-init, so proxied cargo/rustc calls do not map them (and their dependencies) at start-up. They still load from System32 on first use.
---
 build.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/build.rs b/build.rs
index e6e6a69197..07bca81f20 100644
--- a/build.rs
+++ b/build.rs
@@ -70,6 +70,16 @@ fn main() {
     for dll in delay_load_dlls {
         println!("cargo::rustc-link-arg-bin=rustup-init=/delayload:{dll}.dll");
     }
+    // Also delay load system DLLs that the proxies never call. Every `cargo`,
+    // `rustc` etc. started through rustup is a separate process on Windows, and
+    // each of these DLLs (with what it pulls in, such as gdi32 for user32) costs
+    // start-up time when it is loaded eagerly.
+    let delay_load_for_startup = [
+        "user32", "shell32", "ole32", "oleaut32", "crypt32", "secur32", "ws2_32",
+    ];
+    for dll in delay_load_for_startup {
+        println!("cargo::rustc-link-arg-bin=rustup-init=/delayload:{dll}.dll");
+    }
     // When using delayload, it's necessary to also link delayimp.lib
     // https://learn.microsoft.com/en-us/cpp/build/reference/dependentloadflag?view=msvc-170
     println!("cargo::rustc-link-arg-bin=rustup-init=delayimp.lib");

From 958542d47bb7d66569542cb23f382418885123a5 Mon Sep 17 00:00:00 2001
From: Alexandre Zollinger Chohfi <alzollin@microsoft.com>
Date: Thu, 22 Oct 2026 11:20:04 -0700
Subject: [PATCH 2/2] build(windows): don't build test and bench harnesses for
 rustup-init

rustup-init has no unit tests or benchmarks. Building its harnesses with --all-targets applies the binary's link arguments, so the delay-load list is linked without the code that imports user32, and /WX turns LNK4199 into a link error.
---
 Cargo.toml | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Cargo.toml b/Cargo.toml
index 23807c7ad4..3e8a74df81 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -163,6 +163,16 @@ wildcard_imports = "warn"
 name = "rustup"
 path = "src/lib.rs"
 
+[[bin]]
+name = "rustup-init"
+path = "src/bin/rustup-init.rs"
+# The binary has no unit tests or benchmarks. Its empty test and bench harnesses
+# would otherwise be linked with the binary's delay-load list (see `build.rs`) but
+# without the code that imports those DLLs, which `/WX` turns into a link error
+# (LNK4199).
+test = false
+bench = false
+
 [profile.release]
 codegen-units = 1
 lto = true