From 1eed35dddccbcb3a47ffddf999df43ecd1f217ea Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <m@mitchellh.com>
Date: Mon, 23 Mar 2026 11:41:45 -0700
Subject: [PATCH] build: default to MSVC ABI on Windows

Zig defaults to the GNU ABI on Windows, which produces COFF objects
with invalid COMDAT sections in compiler_rt that the MSVC linker
rejects (LNK1143), and uses GNU conventions like ___chkstk_ms that
are unavailable in the MSVC CRT.

Default to the MSVC ABI when no explicit ABI is requested, following
the same pattern as the existing macOS target override. This ensures
compiler_rt produces valid COFF and the generated code uses
MSVC-compatible symbols. Users can still explicitly request the GNU
ABI via -Dtarget.

Also disable bundling ubsan_rt on Windows (its /exclude-symbols
directives are MSVC-incompatible) and add ntdll and kernel32 as
transitive link dependencies for the static library.
---
 src/build/Config.zig       | 13 +++++++++++++
 src/build/GhosttyLibVt.zig |  5 -----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/build/Config.zig b/src/build/Config.zig
index 53d3c737b..eaaeaac90 100644
--- a/src/build/Config.zig
+++ b/src/build/Config.zig
@@ -83,6 +83,19 @@ pub fn init(b: *std.Build, appVersion: []const u8) !Config {
             result = genericMacOSTarget(b, result.query.cpu_arch);
         }
 
+        // On Windows, default to the MSVC ABI so that produced COFF
+        // objects (including compiler_rt) are compatible with the MSVC
+        // linker. Zig defaults to the GNU ABI which produces objects
+        // with invalid COMDAT sections that MSVC rejects (LNK1143).
+        // Only override when no explicit ABI was requested.
+        if (result.result.os.tag == .windows and
+            result.query.abi == null)
+        {
+            var query = result.query;
+            query.abi = .msvc;
+            result = b.resolveTargetQuery(query);
+        }
+
         // If we have no minimum OS version, we set the default based on
         // our tag. Not all tags have a minimum so this may be null.
         if (result.query.os_version_min == null) {
diff --git a/src/build/GhosttyLibVt.zig b/src/build/GhosttyLibVt.zig
index 59e7a46e3..408f1ebc8 100644
--- a/src/build/GhosttyLibVt.zig
+++ b/src/build/GhosttyLibVt.zig
@@ -110,11 +110,6 @@ fn initLib(
         // Zig's ubsan emits /exclude-symbols linker directives that
         // are incompatible with the MSVC linker (LNK4229).
         lib.bundle_ubsan_rt = false;
-
-        // The self-hosted backend produces COFF objects with invalid
-        // COMDAT sections in compiler_rt that the MSVC linker rejects
-        // (LNK1143). Use the LLVM backend to produce valid objects.
-        lib.use_llvm = true;
     }
 
     if (lib.rootModuleTarget().abi.isAndroid()) {