Skip to content

Conversation

Octachron
Copy link
Owner

No description provided.

panglesd and others added 3 commits October 23, 2023 15:50
The parsetree-change label is useful for PPX-related maintainance, this new CI
check enforces that parsetree-change is equivalent to a change in parsetree.mli

Unfortunately, a change in the documentation comments will need a
parsetree-change label.

Signed-off-by: Paul-Elliot <[email protected]>
Octachron pushed a commit that referenced this pull request Jul 26, 2024
…l#13294)

The toplevel printer detects cycles by keeping a hashtable of values
that it has already traversed.

However, some OCaml runtime types (at least bigarrays) may be
partially uninitialized, and hashing them at arbitrary program points
may read uninitialized memory. In particular, the OCaml testsuite
fails when running with a memory-sanitizer enabled, as bigarray
printing results in reads to uninitialized memory:

```
==133712==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x4e6d11 in caml_ba_hash /var/home/edwin/git/ocaml/runtime/bigarray.c:486:45
    #1 0x52474a in caml_hash /var/home/edwin/git/ocaml/runtime/hash.c:251:35
    #2 0x599ebf in caml_interprete /var/home/edwin/git/ocaml/runtime/interp.c:1065:14
    #3 0x5a909a in caml_main /var/home/edwin/git/ocaml/runtime/startup_byt.c:575:9
    #4 0x540ccb in main /var/home/edwin/git/ocaml/runtime/main.c:37:3
    #5 0x7f0910abb087 in __libc_start_call_main (/lib64/libc.so.6+0x2a087) (BuildId: 8f53abaad945a669f2bdcd25f471d80e077568ef)
    #6 0x7f0910abb14a in __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x2a14a) (BuildId: 8f53abaad945a669f2bdcd25f471d80e077568ef)
    #7 0x441804 in _start (/var/home/edwin/git/ocaml/runtime/ocamlrun+0x441804) (BuildId: 7a60eef57e1c2baf770bc38d10d6c227e60ead37)

  Uninitialized value was created by a heap allocation
    #0 0x47d306 in malloc (/var/home/edwin/git/ocaml/runtime/ocamlrun+0x47d306) (BuildId: 7a60eef57e1c2baf770bc38d10d6c227e60ead37)
    #1 0x4e7960 in caml_ba_alloc /var/home/edwin/git/ocaml/runtime/bigarray.c:246:12
    #2 0x4e801f in caml_ba_create /var/home/edwin/git/ocaml/runtime/bigarray.c:673:10
    #3 0x59b8fc in caml_interprete /var/home/edwin/git/ocaml/runtime/interp.c:1058:14
    #4 0x5a909a in caml_main /var/home/edwin/git/ocaml/runtime/startup_byt.c:575:9
    #5 0x540ccb in main /var/home/edwin/git/ocaml/runtime/main.c:37:3
    #6 0x7f0910abb087 in __libc_start_call_main (/lib64/libc.so.6+0x2a087) (BuildId: 8f53abaad945a669f2bdcd25f471d80e077568ef)
    #7 0x7f0910abb14a in __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x2a14a) (BuildId: 8f53abaad945a669f2bdcd25f471d80e077568ef)
    #8 0x441804 in _start (/var/home/edwin/git/ocaml/runtime/ocamlrun+0x441804) (BuildId: 7a60eef57e1c2baf770bc38d10d6c227e60ead37)

SUMMARY: MemorySanitizer: use-of-uninitialized-value /var/home/edwin/git/ocaml/runtime/bigarray.c:486:45 in caml_ba_hash
```

The only use of hashing in genprintval is to avoid cycles, that is, it
is only useful for OCaml values that contain other OCaml values
(including possibly themselves). Bigarrays cannot introduce cycles,
and they are always printed as "<abstr>" anyway.

The present commit proposes to be more conservative in which values
are hashed by the cycle detector to avoid this issue: we skip hashing
any value with tag above No_scan_tag -- which may not contain any
OCaml values.

Suggested-by: Gabriel Scherer <[email protected]>

Signed-off-by: Edwin Török <[email protected]>
Co-authored-by: Edwin Török <[email protected]>
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Projects

None yet

Development

Successfully merging this pull request may close these issues.

2 participants