diff --git a/tool/_testc/python-3.14.8/cpython-pythread.go b/tool/_testc/python-3.14.8/cpython-pythread.go
deleted file mode 100644
index 2a58460e0..000000000
--- a/tool/_testc/python-3.14.8/cpython-pythread.go
+++ /dev/null
@@ -1,17 +0,0 @@
-// Code generated by llcppg; DO NOT EDIT.
-
-package py
-
-import (
-	"github.com/goplus/lib/c"
-	"github.com/goplus/lib/c/pthread"
-	_ "unsafe"
-)
-
-type X_PyTssT struct {
-	X_isInitialized c.Int
-	X_key           pthread.Key
-}
-
-//go:linkname PY_TIMEOUT_MAX C.PY_TIMEOUT_MAX
-var PY_TIMEOUT_MAX c.LongLong
diff --git a/tool/_testc/python-3.14.8/llcppg.cfg b/tool/_testc/python-3.14.8/llcppg.cfg
index 7bb72c8db..998886eec 100644
--- a/tool/_testc/python-3.14.8/llcppg.cfg
+++ b/tool/_testc/python-3.14.8/llcppg.cfg
@@ -17,6 +17,7 @@
 	},
 	"MacroIgnore": [],
 	"TypeIgnore": [],
+	"GroupSubdirBy": "fname",
 	"FailFast": 10,
 	"IgnoreInline": true,
 	"Language": "c"
diff --git a/tool/_testc/python-3.14.8/pythread.go b/tool/_testc/python-3.14.8/pythread.go
index 5691553b7..226402bd6 100644
--- a/tool/_testc/python-3.14.8/pythread.go
+++ b/tool/_testc/python-3.14.8/pythread.go
@@ -2,7 +2,11 @@
 
 package py
 
-import "github.com/goplus/lib/c"
+import (
+	"github.com/goplus/lib/c"
+	"github.com/goplus/lib/c/pthread"
+	_ "unsafe"
+)
 
 type PyLockStatus c.Uint
 
@@ -13,4 +17,11 @@ const (
 )
 
 type PyThreadTypeLock uintptr
+type X_PyTssT struct {
+	X_isInitialized c.Int
+	X_key           pthread.Key
+}
 type PyTssT = X_PyTssT
+
+//go:linkname PY_TIMEOUT_MAX C.PY_TIMEOUT_MAX
+var PY_TIMEOUT_MAX c.LongLong
diff --git a/tool/_testcpp/llvm-22.1.8-support/llcppg-adt.cfg b/tool/_testcpp/llvm-22.1.8-support/llcppg-adt.cfg
index 67318aba9..088690a4c 100644
--- a/tool/_testcpp/llvm-22.1.8-support/llcppg-adt.cfg
+++ b/tool/_testcpp/llvm-22.1.8-support/llcppg-adt.cfg
@@ -14,5 +14,6 @@
 	"Rename": {
 	},
 	"TypeIgnore": [],
-	"NSIgnore": []
+	"NSIgnore": [],
+	"GroupSubdirBy": "dir"
 }
diff --git a/tool/config.go b/tool/config.go
index 5d6fd5d26..59bc91c71 100644
--- a/tool/config.go
+++ b/tool/config.go
@@ -57,7 +57,8 @@ type Config struct {
 	FailFast         int               `json:"FailFast"`         // exit on first N errors, optional
 	IgnoreInline     bool              `json:"IgnoreInline"`     // quietly ignore inline functions
 	NoManglingIgnore bool              `json:"NoManglingIgnore"` // quietly ignore functions with no mangled symbol
-	GroupSubdir      bool              `json:"GroupSubdir"`      // treats sub-directory files as a single file
+	GroupSubdir      bool              `json:"GroupSubdir"`      // treats sub-directory files as a single file. Deprecated: use GroupSubdirBy instead.
+	GroupSubdirBy    string            `json:"GroupSubdirBy"`    // criterion to group sub-directory files by, e.g., "dir" or "fname". `GroupSubdir = true` is equivalent to `GroupSubdirBy = "dir"`.
 }
 
 // -----------------------------------------------------------------------------
diff --git a/tool/gen.go b/tool/gen.go
index 538de20de..fb5b7362b 100644
--- a/tool/gen.go
+++ b/tool/gen.go
@@ -173,7 +173,19 @@ func (cfg *Config) NewPackage(pkgPath, pkgName, workDir string, index clang.Inde
 	}
 	defer DisposeSources(files)
 
-	groupSubdir := cfg.GroupSubdir
+	groupSubdirBy := groupSubdirByNone
+	switch cfg.GroupSubdirBy {
+	case "dir":
+		groupSubdirBy = groupSubdirByDir
+	case "fname":
+		groupSubdirBy = groupSubdirByFname
+	case "":
+		if cfg.GroupSubdir {
+			groupSubdirBy = groupSubdirByDir
+		}
+	default:
+		log.Println("[WARN] unknown GroupSubdirBy value:", cfg.GroupSubdirBy)
+	}
 	srcFilePrefix := dir + string(os.PathSeparator)
 	if pkgName == "" {
 		pkgName = path.Base(cfg.Name)
@@ -216,7 +228,7 @@ func (cfg *Config) NewPackage(pkgPath, pkgName, workDir string, index clang.Inde
 			return
 		},
 		GoFileOf: func(headerFile string) (fname string, ok bool) {
-			return goFileOf(headerFile, srcFilePrefix, groupSubdir)
+			return goFileOf(headerFile, srcFilePrefix, groupSubdirBy)
 		},
 	})
 	return
@@ -232,16 +244,27 @@ func listHeaderFiles(selFiles []string, headerDir string) (topHeaders []string)
 	return
 }
 
-func goFileOf(at, srcFilePrefix string, groupSubdir bool) (fname string, ok bool) {
+const (
+	groupSubdirByNone = iota
+	groupSubdirByDir
+	groupSubdirByFname
+)
+
+func goFileOf(at, srcFilePrefix string, groupSubdirBy int) (fname string, ok bool) {
 	const pathSep = string(os.PathSeparator)
 	const goFileExt = ".go"
 	fname, ok = strings.CutPrefix(at, srcFilePrefix)
 	if ok {
-		if groupSubdir {
+		switch groupSubdirBy {
+		case groupSubdirByDir:
 			if pos := strings.Index(fname, pathSep); pos > 0 {
 				fname = fname[:pos]
 			}
-		} else {
+		case groupSubdirByFname:
+			if pos := strings.LastIndex(fname, pathSep); pos >= 0 {
+				fname = fname[pos+1:]
+			}
+		default:
 			fname = strings.ReplaceAll(fname, pathSep, "-")
 		}
 		if pos := strings.LastIndex(fname, "."); pos > 0 {