hitsumabushi: add PageSize

Closes #26

1.20_linux/runtime/runtime1.go.patch

@@ -14,10 +14,6 @@ func args(c int32, v **byte) {
 }
 //--to
 func args(c int32, v **byte) {
-	// Malloc is not defined yet and getting an address of a global variable might fail here.
-	// Overwrite goargs later.
-
-	physPageSize = 4096
 }
 //--append
 // Expose the entry point for some special environments.

overlay.go

@@ -34,6 +34,7 @@ type config struct {
 	overlayDir       string
 	os               string
 	args             []string
+	pageSize         int
 	clockGettimeName string
 	futexName        string
 	replaceDLLs      []replaceString
@@ -67,7 +68,7 @@ func Args(args ...string) Option {
 // If name is an empty string, the function is not replaced.
 // This is useful for special environments where `clock_gettime` doesn't work correctly.
 //
-// ReplaceClockGettime works only for Linux with Go 1.18 and older.
+// ReplaceClockGettime works only for Linux.
 // For Go 1.19 and newer, use Overlay and ClockFilePath.
 func ReplaceClockGettime(name string) Option {
 	return func(cfg *config) {
@@ -79,7 +80,7 @@ func ReplaceClockGettime(name string) Option {
 // If name is an empty string, a pseudo futex implementation is used.
 // This is useful for special environments where the pseudo `futex` doesn't work correctly.
 //
-// ReplaceFutex works only for Linux with Go 1.18 and older.
+// ReplaceFutex works only for Linux.
 // For Go 1.19 and newer, use Overlay and FutexFilePath.
 func ReplaceFutex(name string) Option {
 	return func(cfg *config) {
@@ -95,6 +96,16 @@ func GOOS(os string) Option {
 	}
 }
 
+// PageSize specifies the page size.
+// The deafult value is 4096.
+//
+// This works only for Linux.
+func PageSize(pageSize int) Option {
+	return func(cfg *config) {
+		cfg.pageSize = pageSize
+	}
+}
+
 // ReplaceDLL replaces a DLL file name loaded at LoadLibraryW and LoadLibraryExW.
 //
 // This works only for Windows.
@@ -139,7 +150,8 @@ func GenOverlayJSON(options ...Option) ([]byte, error) {
 	}
 
 	cfg := config{
-		os: runtime.GOOS,
+		os:       runtime.GOOS,
+		pageSize: 4096,
 	}
 	for _, op := range options {
 		op(&cfg)
@@ -301,6 +313,14 @@ func goargs() {
 			}
 		}
 
+		{
+			old := `var physPageSize uintptr`
+			new := fmt.Sprintf(`var physPageSize uintptr = %d`, cfg.pageSize)
+			if err := replace(tmpDir, replaces, "runtime", "malloc.go", old, new, cfg.os); err != nil {
+				return nil, err
+			}
+		}
+
 		// Replace clock_gettime.
 		if cfg.clockGettimeName != "" {
 			old := "#define clock_gettime clock_gettime"