From ef36e4fd0eec3283a43d03bc6bff7da4e5e03c06 Mon Sep 17 00:00:00 2001 From: Cherry Zhang Date: Tue, 13 Apr 2021 23:41:45 -0400 Subject: [PATCH] reflect: keep pointer register results alive in callMethod When callMethod calls the underlying method, after reflectcall it gets the result registers in "Ints" slots but not in "Ptrs" slots. If the GC runs at this point, it may lose track of those pointers and free the memory they point to. To make sure the GC sees the pointer results, copy "Ints" to "Ptrs", and keep them alive until we return to the caller. This fixes test/fixedbugs/issue27695.go with register ABI. Change-Id: I4092c91bcbd6954683740a12d91d689900446875 Reviewed-on: https://go-review.googlesource.com/c/go/+/309909 Trust: Cherry Zhang Run-TryBot: Cherry Zhang TryBot-Result: Go Bot Reviewed-by: Michael Knyszek --- src/reflect/abi.go | 16 ++++++++++++++++ src/reflect/value.go | 8 ++++++++ 2 files changed, 24 insertions(+) diff --git a/src/reflect/abi.go b/src/reflect/abi.go index caa770fcb0..17b79a8394 100644 --- a/src/reflect/abi.go +++ b/src/reflect/abi.go @@ -366,6 +366,22 @@ func (a *abiDesc) dump() { println("stackCallArgsSize", a.stackCallArgsSize) println("retOffset", a.retOffset) println("spill", a.spill) + print("inRegPtrs:") + dumpPtrBitMap(a.inRegPtrs) + println() + print("outRegPtrs:") + dumpPtrBitMap(a.outRegPtrs) + println() +} + +func dumpPtrBitMap(b abi.IntArgRegBitmap) { + for i := 0; i < intArgRegs; i++ { + x := 0 + if b.Get(i) { + x = 1 + } + print(" ", x) + } } func newAbiDesc(t *funcType, rcvr *rtype) abiDesc { diff --git a/src/reflect/value.go b/src/reflect/value.go index 7890c125d8..6f1a3c02d6 100644 --- a/src/reflect/value.go +++ b/src/reflect/value.go @@ -1023,6 +1023,9 @@ func callMethod(ctxt *methodValue, frame unsafe.Pointer, retValid *bool, regs *a methodFrameSize = align(methodFrameSize, ptrSize) methodFrameSize += methodABI.spill + // Mark pointers in registers for the return path. + methodRegs.ReturnIsPtr = methodABI.outRegPtrs + // Call. // Call copies the arguments from scratch to the stack, calls fn, // and then copies the results back into scratch. @@ -1059,6 +1062,11 @@ func callMethod(ctxt *methodValue, frame unsafe.Pointer, retValid *bool, regs *a // See the comment in callReflect. runtime.KeepAlive(ctxt) + + // Keep valueRegs alive because it may hold live pointer results. + // The caller (methodValueCall) has it as a stack object, which is only + // scanned when there is a reference to it. + runtime.KeepAlive(valueRegs) } // funcName returns the name of f, for use in error messages. -- 2.50.0