Dangling pointers are not a problem unless they are dereferenced and used. However, they are a source of UaF bugs and highly discouraged unless you are 100% confident that they are never dereferenced after the pointed-to objects are freed.
Behind build flags, Chrome implements a dangling pointer detector. It causes Chrome to crash, whenever a raw_ptr becomes dangling:
raw_ptr<T> ptr_never_dangling;
On the other hand, we cannot simply ban all the usage of dangling pointers
because there are valid use cases. The DisableDanglingPtrDetection
option can
be used to annotate "intentional-and-safe" dangling pointers. It is meant to be
used as a last resort, only if there is no better way to re-architecture the
code.
raw_ptr<T, DisableDanglingPtrDetection> ptr_may_dangle;
It is gated behind both build and runtime flags:
gn args ./out/dangling/
use_goma = true
is_debug = false
dcheck_always_on = true
use_backup_ref_ptr = true
use_partition_alloc = true
enable_dangling_raw_ptr_checks = true
./out/dangling/content_shell --enable-features=PartitionAllocBackupRefPtr
Chrome will crash on the first dangling raw_ptr detected.
Instead of immediately crashing, you can list all the dangling raw_ptr
occurrences. This is gated behind the PartitionAllocDanglingPtrRecord
feature.
For instance:
./out/dangling/content_shell --enable-features=PartitionAllocBackupRefPtr,PartitionAllocDanglingPtrRecord |& tee output
The logs can be filtered and transformed into a tab separated table:
cat output \
| grep "DanglingSignature" \
| cut -f2,3 \
| sort \
| uniq -c \
| sed -E 's/^ *//; s/ /\t/' \
| sort -rn
This is used to list issues and track progresses.