From 63260ec7221741fb0c0a0e2f1018da094b116af9 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <m@mitchellh.com>
Date: Mon, 23 Mar 2026 12:31:17 -0700
Subject: [PATCH] build: disable ubsan for SIMD C++ files on MSVC

The SIMD C++ files reference __ubsan_handle_* symbols when compiled
in debug mode, but we do not link or bundle the ubsan runtime on
MSVC. This matches what the highway and simdutf packages already do
in their own build files.
---
 src/build/SharedDeps.zig | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/build/SharedDeps.zig b/src/build/SharedDeps.zig
index 573c68b74..e01adb1fa 100644
--- a/src/build/SharedDeps.zig
+++ b/src/build/SharedDeps.zig
@@ -812,6 +812,14 @@ pub fn addSimd(
             "-std=c++17",
         );
 
+        // Disable ubsan for MSVC to avoid undefined references to
+        // __ubsan_handle_* symbols that require a runtime we don't link
+        // and bundle. Hopefully we can fix this one day since ubsan is nice!
+        if (target.result.abi == .msvc) try flags.appendSlice(b.allocator, &.{
+            "-fno-sanitize=undefined",
+            "-fno-sanitize-trap=undefined",
+        });
+
         m.addCSourceFiles(.{
             .files = &.{
                 "src/simd/base64.cpp",