Skip to content

Extend support for 4.10.0 nnp check to msvc64#5

Merged
kayceesrk merged 2 commits intokayceesrk:4.10.0+nnp+checkfrom
dra27:nnpcheck-msvc64
Sep 5, 2020
Merged

Extend support for 4.10.0 nnp check to msvc64#5
kayceesrk merged 2 commits intokayceesrk:4.10.0+nnp+checkfrom
dra27:nnpcheck-msvc64

Conversation

@dra27
Copy link
Copy Markdown

@dra27 dra27 commented Sep 4, 2020

This incorporates @stedolan's alternate function for msvc64 and @nojb observation that 1ul is the wrong size on Windows! I realise I was probably overly pedantic sticking with 1ul for Linux, but I only realise that after I'd committed it........

@kayceesrk
Copy link
Copy Markdown
Owner

Thanks! It is surprising that 1ul is not 64-bits on Windows. Importantly, does this catch naked pointers on msvc64? :-) Curious what the performance overhead is with the use of exceptions.

@kayceesrk
Copy link
Copy Markdown
Owner

I noticed ocaml#9534 (comment) only after posting the previous comment. I shall merge this one. Thanks!

@kayceesrk kayceesrk merged commit d7c7f5d into kayceesrk:4.10.0+nnp+check Sep 5, 2020
@nojb
Copy link
Copy Markdown

nojb commented Sep 5, 2020

Thanks! It is surprising that 1ul is not 64-bits on Windows. Importantly, does this catch naked pointers on msvc64? :-) Curious what the performance overhead is with the use of exceptions.

For info, long (and int) is always 32-bit on Windows (both 32- and 64-bits) so that code written for 32-bits can be recompiled without any change under 64-bits.

@dra27 dra27 deleted the nnpcheck-msvc64 branch July 6, 2021 16:16
kayceesrk pushed a commit that referenced this pull request Aug 21, 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 <gabriel.scherer@gmail.com>

Signed-off-by: Edwin Török <edwin.torok@cloud.com>
Co-authored-by: Edwin Török <edwin.torok@cloud.com>
kayceesrk pushed a commit that referenced this pull request Jul 30, 2025
Move the orphaned ephemerons GC colour check inside the barrier.
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Labels

None yet

Projects

None yet

Development

Successfully merging this pull request may close these issues.

3 participants