From 777c02825229f14cf91c6044827ea42a77ded4a3 Mon Sep 17 00:00:00 2001 From: Ian Lance Taylor Date: Sat, 17 Aug 2019 04:35:37 +0000 Subject: [PATCH] runtime: scan write barrier buffer conservatively In gccgo, we insert the write barriers in the frontend, and so we cannot completely prevent write barriers on stack writes. So it is possible for a bad pointer appearing in the write barrier buffer. When flushing the write barrier, treat it the same as sacnning the stack. In particular, don't mark a pointer if it does not point to an allocated object. We already have similar logic in greyobject. With this, hopefully, we can prevent an unallocated object from being marked completely. Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/190599 From-SVN: r274598 --- gcc/go/gofrontend/MERGE | 2 +- libgo/go/runtime/mwbbuf.go | 9 ++++++++- 2 files changed, 9 insertions(+), 2 deletions(-) diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE index 48b42496965..78597da6417 100644 --- a/gcc/go/gofrontend/MERGE +++ b/gcc/go/gofrontend/MERGE @@ -1,4 +1,4 @@ -0f6d673d5b1a3474c3424cb6994ae8ff9baed255 +838f926c93898767f0337122725a4f52a1335186 The first line of this file holds the git revision number of the last merge done from the gofrontend repository. diff --git a/libgo/go/runtime/mwbbuf.go b/libgo/go/runtime/mwbbuf.go index 4c875ff2d15..a27406e2987 100644 --- a/libgo/go/runtime/mwbbuf.go +++ b/libgo/go/runtime/mwbbuf.go @@ -285,10 +285,17 @@ func wbBufFlush1(_p_ *p) { // path to reduce the rate of flushes? continue } - obj, span, objIndex := findObject(ptr, 0, 0, false) + obj, span, objIndex := findObject(ptr, 0, 0, !usestackmaps) if obj == 0 { continue } + if span.isFree(objIndex) { + // For gccgo, it is possible that we have a write barrier + // writing to unintialized stack memory. So we could see + // a bad pointer in the write barrier buffer. Don't mark + // it in this case. + continue + } // TODO: Consider making two passes where the first // just prefetches the mark bits. mbits := span.markBitsForIndex(objIndex)