From 1a4cb2032e2a7346c449205abd36fe4ed8f4db70 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Fri, 7 Aug 2026 10:20:57 -0700
Subject: [PATCH] runtime: test container GC layouts

---
 testdata/gc.go | 151 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 150 insertions(+), 1 deletion(-)

diff --git a/testdata/gc.go b/testdata/gc.go
index 456d763b4..445290cbb 100644
--- a/testdata/gc.go
+++ b/testdata/gc.go
@@ -1,6 +1,9 @@
 package main
 
-import "runtime"
+import (
+	"reflect"
+	"runtime"
+)
 
 var xorshift32State uint32 = 1
 
@@ -19,6 +22,9 @@ func randuint32() uint32 {
 
 func main() {
 	testNonPointerHeap()
+	testGlobalMapRoots()
+	testGlobalChannelRoots()
+	testReflectRoots()
 	testKeepAlive()
 }
 
@@ -74,3 +80,146 @@ func testKeepAlive() {
 	var x int
 	runtime.KeepAlive(&x)
 }
+
+type globalMapObject struct {
+	marker int
+	data   [64]byte
+}
+
+var globalMap = make(map[int]*globalMapObject)
+var globalChannel chan *globalMapObject
+var globalPointerSlice []*globalMapObject
+var globalGCClobber any
+
+type globalMapLargeKey struct {
+	object *globalMapObject
+	data   [129]byte
+}
+
+type globalMapLargeValue struct {
+	object *globalMapObject
+	data   [129]byte
+}
+
+var globalLargeKeyMap = make(map[globalMapLargeKey]int)
+var globalLargeValueMap = make(map[int]globalMapLargeValue)
+
+//go:noinline
+func populateGlobalMaps() {
+	for i := 0; i < 32; i++ {
+		globalMap[i] = &globalMapObject{marker: 100 + i}
+		globalPointerSlice = append(globalPointerSlice, &globalMapObject{marker: 800 + i})
+	}
+	globalLargeKeyMap[globalMapLargeKey{
+		object: &globalMapObject{marker: 200},
+	}] = 1
+	globalLargeValueMap[0] = globalMapLargeValue{
+		object: &globalMapObject{marker: 300},
+	}
+}
+
+func testGlobalMapRoots() {
+	populateGlobalMaps()
+
+	runtime.GC()
+	for i := 0; i < 100; i++ {
+		globalGCClobber = new(globalMapObject)
+	}
+	runtime.GC()
+
+	for i := 0; i < 32; i++ {
+		if globalMap[i].marker != 100+i {
+			panic("global map value was collected")
+		}
+	}
+	for key := range globalLargeKeyMap {
+		if key.object.marker != 200 {
+			panic("indirect global map key was collected")
+		}
+	}
+	if globalLargeValueMap[0].object.marker != 300 {
+		panic("indirect global map value was collected")
+	}
+	for i, object := range globalPointerSlice {
+		if object.marker != 800+i {
+			panic("global slice value was collected")
+		}
+	}
+}
+
+//go:noinline
+func populateGlobalChannel() {
+	globalChannel = make(chan *globalMapObject, 4)
+	globalChannel <- &globalMapObject{marker: 400}
+}
+
+func testGlobalChannelRoots() {
+	populateGlobalChannel()
+
+	runtime.GC()
+	for i := 0; i < 100; i++ {
+		globalGCClobber = new(globalMapObject)
+	}
+	runtime.GC()
+
+	if (<-globalChannel).marker != 400 {
+		panic("global channel value was collected")
+	}
+}
+
+type reflectRootObject struct {
+	marker int
+	child  *reflectRootObject
+	data   [128]byte
+}
+
+type reflectMapKey struct {
+	object *reflectRootObject
+	data   [129]byte
+}
+
+type reflectMapValue struct {
+	object *reflectRootObject
+	data   [129]byte
+}
+
+type reflectRootMap map[reflectMapKey]reflectMapValue
+
+var globalReflectObject *reflectRootObject
+var globalReflectMap reflectRootMap
+
+//go:noinline
+func populateReflectRoots() {
+	value := reflect.New(reflect.TypeOf(reflectRootObject{}))
+	globalReflectObject = value.Interface().(*reflectRootObject)
+	globalReflectObject.child = &reflectRootObject{marker: 500}
+
+	mapValue := reflect.MakeMapWithSize(reflect.TypeOf(globalReflectMap), 1)
+	mapValue.SetMapIndex(
+		reflect.ValueOf(reflectMapKey{object: &reflectRootObject{marker: 600}}),
+		reflect.ValueOf(reflectMapValue{object: &reflectRootObject{marker: 700}}),
+	)
+	globalReflectMap = mapValue.Interface().(reflectRootMap)
+}
+
+func testReflectRoots() {
+	populateReflectRoots()
+
+	runtime.GC()
+	for i := 0; i < 100; i++ {
+		globalGCClobber = new(reflectRootObject)
+	}
+	runtime.GC()
+
+	if globalReflectObject.child.marker != 500 {
+		panic("reflected object field was collected")
+	}
+	for key, value := range globalReflectMap {
+		if key.object.marker != 600 {
+			panic("reflected map key was collected")
+		}
+		if value.object.marker != 700 {
+			panic("reflected map value was collected")
+		}
+	}
+}