runtime: eagerly mark Boehm global roots

src/runtime/gc_boehm.go

@@ -165,6 +165,9 @@ func libgc_size(ptr uintptr) uintptr
 //export GC_push_all
 func libgc_push_all(bottom, top uintptr)
 
+//export GC_push_all_eager
+func libgc_push_all_eager(bottom, top uintptr)
+
 //export GC_push_all_stack
 func libgc_push_all_stack(bottom, top uintptr)
 

src/runtime/gc_globals_range.go

@@ -5,31 +5,12 @@ package runtime
 import "unsafe"
 
 func markGlobals() {
-	rangeCount := gcGlobalRootCount()
-	if rangeCount == 0 {
-		return
+	for i := uintptr(0); i < gcGlobalRootCount(); i++ {
+		addr := gcGlobalRoot(uintptr(i))
+		// GC_push_all queues one range per call and overflows Boehm's mark
+		// stack for programs with thousands of roots. Scan each range now.
+		libgc_push_all_eager(uintptr(addr), uintptr(addr)+gcGlobalRootSize(i))
 	}
-
-	var rootCount uintptr
-	for i := uintptr(0); i < rangeCount; i++ {
-		rootCount += gcGlobalRootSize(i) / unsafe.Sizeof(uintptr(0))
-	}
-
-	// markRoots only accepts a range, so copy all global pointers into
-	// contiguous scratch space for marking.
-	roots := unsafe.Slice((*uintptr)(gcGlobalRootValues()), rootCount)
-	var rootIndex uintptr
-	for i := uintptr(0); i < rangeCount; i++ {
-		addr := gcGlobalRoot(i)
-		size := gcGlobalRootSize(i)
-		for offset := uintptr(0); offset < size; offset += unsafe.Sizeof(uintptr(0)) {
-			roots[rootIndex] = *(*uintptr)(unsafe.Add(addr, offset))
-			rootIndex++
-		}
-	}
-
-	start := uintptr(unsafe.Pointer(&roots[0]))
-	markRoots(start, start+rootCount*unsafe.Sizeof(roots[0]))
 }
 
 // These functions are generated by the compiler from the pointer layouts of
@@ -37,4 +18,3 @@ func markGlobals() {
 func gcGlobalRootCount() uintptr
 func gcGlobalRoot(index uintptr) unsafe.Pointer
 func gcGlobalRootSize(index uintptr) uintptr
-func gcGlobalRootValues() unsafe.Pointer

transform/testdata/gc-stackslots.ll

@@ -19,8 +19,6 @@ declare ptr @runtime.gcGlobalRoot(i32)
 
 declare i32 @runtime.gcGlobalRootSize(i32)
 
-declare ptr @runtime.gcGlobalRootValues()
-
 ; Generic function that returns a pointer (that must be tracked).
 define ptr @getPointer() {
     ret ptr @someGlobal

transform/testdata/gc-stackslots.out.ll

@@ -9,7 +9,6 @@ target triple = "wasm32-unknown-unknown-wasm"
 @ptrArrayGlobal = global [8 x ptr] zeroinitializer
 @constantPtrGlobal = constant ptr @someGlobal
 @runtime.gcGlobalRoots = internal constant [4 x { ptr, i32 }] [{ ptr, i32 } { ptr @ptrGlobal, i32 4 }, { ptr, i32 } { ptr @structGlobal, i32 4 }, { ptr, i32 } { ptr getelementptr (i8, ptr @structGlobal, i32 8), i32 8 }, { ptr, i32 } { ptr @ptrArrayGlobal, i32 32 }]
-@runtime.gcGlobalRootValueArray = internal global [12 x i32] zeroinitializer
 
 declare void @runtime.trackPointer(ptr nocapture readonly)
 
@@ -36,11 +35,6 @@ entry:
   ret i32 %3
 }
 
-define ptr @runtime.gcGlobalRootValues() {
-entry:
-  ret ptr @runtime.gcGlobalRootValueArray
-}
-
 define ptr @getPointer() {
   ret ptr @someGlobal
 }