Revised handling of the list of all opened channels #7
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Octachron
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May 20, 2022
runtime/io.c
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| /* Testing channel->fd >= 0 looks unnecessary, as | ||
| caml_ml_close_channel changes max when setting fd to -1. */ | ||
| if (channel->max == NULL | ||
| && channel->flags & CHANNEL_FLAG_MANAGED_BY_GC) { |
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Shouldn't we remove this part of the test or replace it by an assert now that we only link gc-managed channels?
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Yes, absolutely. Will put an assertion.
|
Thanks! I was visibly missing a forest behind the tree this time. I will review the changes properly and probably merge them in this PR branch. |
- Don't put channels opened from C on this list, only those opened from OCaml and tracked by the GC. - Simplify several functions accordingly. - Fix an error in caml_finalize_channel where the channel could be unlinked from the list, then not freed because not flushed.
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Well, this code is complicated to begin with, and went through (too?) many iterations and incremental changes already. I considered putting output channels only in the doubly-linked list used by |
Octachron
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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]>
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This is a variant on @Octachron's PR about I/O channels.
It simplifies the code by not putting channels opened from C on the list of all opened channels, only those opened from OCaml
and tracked by the GC.
It also fixes an earlier error in
caml_finalize_channelwhere the channel could be unlinked from the list, then not freed because not flushed. But it will never be flushed duringat_exitsince it was unlinked !