FW: adding a red zone at the start of the allocation cause GC issue

135 views
Skip to first unread message

Fannie Zhang

unread,
Nov 9, 2021, 8:21:49 PM11/9/21
to golan...@googlegroups.com

Hi all,

 

Recently, some Asan enabling patches have been merged into master. But the CL  https://go-review.googlesource.com/c/go/+/298614 only adds a red zone at the end of the allocation, it may cause -asan option to fail to detect underflows, Ian commented on this CL that a red zone may be added at the start of the allocation.  

 

Unfortunately, the modification will cause a GC issue.  Because the process of Go memory allocation and GC are closely linked, like mallocgc() calls heapBitsSetType() to set heap bitmap for the new allocation.

 

If adding a red zone at the start of the allocation, the allocated pointer that returned is not equal to  “(span().base  +  s.elemsize*freeidx), it is equal to “(span().base +s.elemsize*freeidx + redZoneSize)”. I do not know whether this behavior will break some of underlying assumptions in GC.

 

The modification patch is https://go-review.googlesource.com/c/go/+/361966.

The test case is https://play.golang.org/p/B_nXGywju4w.

The command: go run -asan test.go

 

I am not very familiar with the whole GC process, the related change may be wrong, or it may miss important things.  If you have time, can you please take a look and give me some comments?

 

Thank you very much!

 

Best regards,

Fannie Zhang

Keith Randall

unread,
Nov 10, 2021, 1:51:21 AM11/10/21
to Fannie Zhang, golan...@googlegroups.com
Yes, it is tricky.
I tried to do a similar thing in https://go-review.googlesource.com/c/go/+/315029 , but ended up only getting it to work for tinyalloc.


--
You received this message because you are subscribed to the Google Groups "golang-dev" group.
To unsubscribe from this group and stop receiving emails from it, send an email to golang-dev+...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/golang-dev/PAXPR08MB6640BF62E7648E3D3B32D85894939%40PAXPR08MB6640.eurprd08.prod.outlook.com.
Reply all
Reply to author
Forward
0 new messages