From 1e7c81b2d9a20ad6cae8b938a4d8fb1b34c83808 Mon Sep 17 00:00:00 2001
From: Chris Denton <chris@chrisdenton.dev>
Date: Fri, 3 Jul 2026 17:44:58 +0000
Subject: [PATCH] Look for cdb location in the registry first

This is more robust then assuming it's in Program Files. We still fallback to Program Files as a last resort.
---
 src/bootstrap/Cargo.lock                | 12 +++++++++
 src/bootstrap/Cargo.toml                |  3 +++
 src/bootstrap/src/core/debuggers/cdb.rs | 35 ++++++++++++++++---------
 3 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/src/bootstrap/Cargo.lock b/src/bootstrap/Cargo.lock
index 7c890e3f2004c..f988d207529b6 100644
--- a/src/bootstrap/Cargo.lock
+++ b/src/bootstrap/Cargo.lock
@@ -71,6 +71,7 @@ dependencies = [
  "tracing-subscriber",
  "walkdir",
  "windows 0.61.1",
+ "windows-registry",
  "xz2",
 ]
 
@@ -1095,6 +1096,17 @@ dependencies = [
  "windows-link 0.2.1",
 ]
 
+[[package]]
+name = "windows-registry"
+version = "0.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "02752bf7fbdcce7f2a27a742f798510f3e5ad88dbe84871e5168e2120c3d5720"
+dependencies = [
+ "windows-link 0.2.1",
+ "windows-result 0.4.1",
+ "windows-strings 0.5.1",
+]
+
 [[package]]
 name = "windows-result"
 version = "0.3.2"
diff --git a/src/bootstrap/Cargo.toml b/src/bootstrap/Cargo.toml
index 60e52102dc46b..b2e8c42adf48b 100644
--- a/src/bootstrap/Cargo.toml
+++ b/src/bootstrap/Cargo.toml
@@ -66,6 +66,9 @@ tracing = { version = "0.1", optional = true, features = ["attributes"] }
 tracing-chrome = { version = "0.7", optional = true }
 tracing-subscriber = { version = "0.3", optional = true, features = ["env-filter", "fmt", "registry", "std"] }
 
+[target.'cfg(windows)'.dependencies.windows-registry]
+version = "0.6"
+
 [target.'cfg(windows)'.dependencies.junction]
 version = "1.3.0"
 
diff --git a/src/bootstrap/src/core/debuggers/cdb.rs b/src/bootstrap/src/core/debuggers/cdb.rs
index a19b70477ecfe..7f835f3618724 100644
--- a/src/bootstrap/src/core/debuggers/cdb.rs
+++ b/src/bootstrap/src/core/debuggers/cdb.rs
@@ -7,15 +7,12 @@ pub(crate) struct Cdb {
     pub(crate) cdb: PathBuf,
 }
 
-/// FIXME: This CDB discovery code was very questionable when it was in
-/// compiletest, and it's just as questionable now that it's in bootstrap.
+/// We consult the registry to find the installed cdb.exe and try "Program Files" if that fails.
 pub(crate) fn discover_cdb(target: TargetSelection) -> Option<Cdb> {
     if !cfg!(windows) || !target.ends_with("-pc-windows-msvc") {
         return None;
     }
 
-    let pf86 =
-        PathBuf::from(env::var_os("ProgramFiles(x86)").or_else(|| env::var_os("ProgramFiles"))?);
     let cdb_arch = if cfg!(target_arch = "x86") {
         "x86"
     } else if cfg!(target_arch = "x86_64") {
@@ -28,14 +25,28 @@ pub(crate) fn discover_cdb(target: TargetSelection) -> Option<Cdb> {
         return None; // No compatible CDB.exe in the Windows 10 SDK
     };
 
-    let mut path = pf86;
-    path.push(r"Windows Kits\10\Debuggers"); // We could check 8.1 etc. too?
-    path.push(cdb_arch);
-    path.push(r"cdb.exe");
+    let path = discover_cdb_registry(cdb_arch).or_else(|| discover_cdb_program_files(cdb_arch))?;
+    Some(Cdb { cdb: path })
+}
 
-    if !path.exists() {
-        return None;
-    }
+#[cfg(windows)]
+fn discover_cdb_registry(cdb_arch: &'static str) -> Option<PathBuf> {
+    use windows_registry::LOCAL_MACHINE;
+    let roots = LOCAL_MACHINE.open(r"SOFTWARE\Microsoft\Windows Kits\Installed Roots").ok()?;
+    // "KitsRoot10" is used by both the Windows 10 and 11 SDKs.
+    let mut path: PathBuf = roots.get_string("KitsRoot10").ok()?.into();
+    path.extend([r"Debuggers", cdb_arch, r"cdb.exe"]);
+    path.exists().then_some(path)
+}
 
-    Some(Cdb { cdb: path })
+#[cfg(not(windows))]
+fn discover_cdb_registry(_cdb_arch: &'static str) -> Option<PathBuf> {
+    None
+}
+
+fn discover_cdb_program_files(cdb_arch: &'static str) -> Option<PathBuf> {
+    let mut path =
+        PathBuf::from(env::var_os("ProgramFiles(x86)").or_else(|| env::var_os("ProgramFiles"))?);
+    path.extend([r"Windows Kits\10\Debuggers", cdb_arch, r"cdb.exe"]);
+    path.exists().then_some(path)
 }