From b1ac97db88406492de5618ad0ad783867f74e281 Mon Sep 17 00:00:00 2001
From: Maksim An <maksiman@microsoft.com>
Date: Mon, 13 Apr 2026 16:48:13 -0700
Subject: [PATCH] Log cimwriter.dll version on load

Add getFileVersion/formatFileVersion helpers to extract the PE
file version from the loaded DLL and include it in the existing
log line. Add unit tests for version extraction.

Ref: https://learn.microsoft.com/en-us/windows/win32/api/verrsrc/ns-verrsrc-vs_fixedfileinfo

Signed-off-by: Maksim An <maksiman@microsoft.com>
---
 internal/winapi/cimwriter/cimwriter.go      | 37 +++++++++++++++-
 internal/winapi/cimwriter/cimwriter_test.go | 47 +++++++++++++++++++++
 2 files changed, 83 insertions(+), 1 deletion(-)
 create mode 100644 internal/winapi/cimwriter/cimwriter_test.go

diff --git a/internal/winapi/cimwriter/cimwriter.go b/internal/winapi/cimwriter/cimwriter.go
index 5d58e487d6..d8f4d4dc12 100644
--- a/internal/winapi/cimwriter/cimwriter.go
+++ b/internal/winapi/cimwriter/cimwriter.go
@@ -3,7 +3,9 @@
 package cimwriter
 
 import (
+	"fmt"
 	"sync"
+	"unsafe"
 
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/windows"
@@ -53,7 +55,12 @@ var load = sync.OnceValue(func() error {
 	var buf [windows.MAX_PATH]uint16
 	n, _ := windows.GetModuleFileName(windows.Handle(modcimwriter.Handle()), &buf[0], uint32(len(buf)))
 	if n > 0 {
-		logrus.WithField("path", windows.UTF16ToString(buf[:n])).Info("loaded cimwriter.dll")
+		path := windows.UTF16ToString(buf[:n])
+		fields := logrus.Fields{"path": path}
+		if ver, err := getFileVersion(path); err == nil {
+			fields["version"] = ver
+		}
+		logrus.WithFields(fields).Info("loaded cimwriter.dll")
 	}
 	return nil
 })
@@ -62,3 +69,31 @@ var load = sync.OnceValue(func() error {
 func Supported() bool {
 	return load() == nil
 }
+
+// getFileVersion returns the file version string (e.g. "10.0.26100.1") for the given path.
+func getFileVersion(path string) (string, error) {
+	size, err := windows.GetFileVersionInfoSize(path, nil)
+	if err != nil {
+		return "", err
+	}
+	data := make([]byte, size)
+	if err := windows.GetFileVersionInfo(path, 0, size, unsafe.Pointer(&data[0])); err != nil {
+		return "", err
+	}
+	var info *windows.VS_FIXEDFILEINFO
+	var infoLen uint32
+	if err := windows.VerQueryValue(unsafe.Pointer(&data[0]), `\`, unsafe.Pointer(&info), &infoLen); err != nil {
+		return "", err
+	}
+	return formatFileVersion(info), nil
+}
+
+// formatFileVersion formats the file version from a VS_FIXEDFILEINFO as "major.minor.build.revision".
+// See https://learn.microsoft.com/en-us/windows/win32/api/verrsrc/ns-verrsrc-vs_fixedfileinfo
+func formatFileVersion(info *windows.VS_FIXEDFILEINFO) string {
+	major := info.FileVersionMS >> 16
+	minor := info.FileVersionMS & 0xffff
+	build := info.FileVersionLS >> 16
+	revision := info.FileVersionLS & 0xffff
+	return fmt.Sprintf("%d.%d.%d.%d", major, minor, build, revision)
+}
diff --git a/internal/winapi/cimwriter/cimwriter_test.go b/internal/winapi/cimwriter/cimwriter_test.go
new file mode 100644
index 0000000000..49ce50a992
--- /dev/null
+++ b/internal/winapi/cimwriter/cimwriter_test.go
@@ -0,0 +1,47 @@
+//go:build windows
+
+package cimwriter
+
+import (
+	"os"
+	"regexp"
+	"testing"
+)
+
+func TestGetFileVersion_Kernel32(t *testing.T) {
+	// kernel32.dll is always present and always has version info.
+	path := os.Getenv("SystemRoot") + `\System32\kernel32.dll`
+	ver, err := getFileVersion(path)
+	if err != nil {
+		t.Fatalf("getFileVersion(%q) failed: %v", path, err)
+	}
+	// Version should match "major.minor.build.revision" pattern.
+	matched, _ := regexp.MatchString(`^\d+\.\d+\.\d+\.\d+$`, ver)
+	if !matched {
+		t.Fatalf("unexpected version format: %q", ver)
+	}
+	t.Logf("kernel32.dll version: %s", ver)
+}
+
+func TestGetFileVersion_NonexistentFile(t *testing.T) {
+	_, err := getFileVersion(`C:\nonexistent_path\fake.dll`)
+	if err == nil {
+		t.Fatal("expected error for nonexistent file, got nil")
+	}
+}
+
+func TestGetFileVersion_CimwriterDLL(t *testing.T) {
+	if !Supported() {
+		t.Skip("cimwriter.dll is not supported on this system")
+	}
+	path := os.Getenv("SystemRoot") + `\System32\cimwriter.dll`
+	ver, err := getFileVersion(path)
+	if err != nil {
+		t.Fatalf("getFileVersion(%q) failed: %v", path, err)
+	}
+	matched, _ := regexp.MatchString(`^\d+\.\d+\.\d+\.\d+$`, ver)
+	if !matched {
+		t.Fatalf("unexpected version format: %q", ver)
+	}
+	t.Logf("cimwriter.dll version: %s", ver)
+}