From 6a650941d28c8bf1b8453340eb6f3ccca2ff6453 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard@metafoo.co.uk>
Date: Thu, 5 Mar 2026 12:01:44 -0800
Subject: [PATCH] Don't run clang to link when fuzzing. (#6835)

The clang driver is too easy to crash with fuzzer-generated command
lines, and it's not interesting to find those bugs.
---
 toolchain/driver/link_subcommand.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/toolchain/driver/link_subcommand.cpp b/toolchain/driver/link_subcommand.cpp
index 1ebdca573f99..99f4a4d5ef36 100644
--- a/toolchain/driver/link_subcommand.cpp
+++ b/toolchain/driver/link_subcommand.cpp
@@ -117,6 +117,11 @@ auto LinkSubcommand::Run(DriverEnv& driver_env) -> DriverResult {
 
   ClangRunner runner(driver_env.installation, driver_env.fs,
                      driver_env.vlog_stream);
+  // Don't run Clang when fuzzing, it is known to not be reliable under fuzzing
+  // due to many unfixed issues.
+  if (TestAndDiagnoseIfFuzzingExternalLibraries(driver_env, "clang")) {
+    return {.success = false};
+  }
   ErrorOr<bool> run_result =
       driver_env.prebuilt_runtimes
           ? runner.RunWithPrebuiltRuntimes(clang_args,