Dear OCaml users, 

We have the pleasure of announcing the release of OCaml 5.2.1, dedicated to the 
memory of Niels Bohr and Paul Éluard on the anniversary of their deaths. 

OCaml 5.2.1 is a collection of safe but import runtime time bug fixes backported 
from the 5.3 branch of OCaml to improve the stability of the 5.2 runtime while waiting for the 
upcoming release of OCaml 5.3.0. 

The full list of bug fixes is available below for more details. 

Happy hacking, 
-- Florian Angeletti, for the OCaml team. 

Installation Instructions 
------------------------------- 

The base compiler can be installed as an opam switch with the following commands: 

opam update 
opam switch create 5.2.1 

The source code for the release is also directly available on: 

* GitHub: https://github.com/ocaml/ocaml/archive/5.2.1.tar.gz) 
* Inria archive: https://caml.inria.fr/pub/distrib/ocaml-5.2/ocaml-5.2.1.tar.gz 


Bug Fixes In OCaml 5.2.1 (18 November 2024) 
------------------------------------------------------------- 

- #13207(https://github.com/ocaml/ocaml/issues/13207): Be sure to reload the register caching the exception handler in 
`caml_c_call` and `caml_c_call_stack_args`, as its value may have been changed 
if the OCaml stack is expanded during a callback. 
(Miod Vallat, report by Vesa Karvonen, review by Gabriel Scherer and 
Xavier Leroy) 

- #13252(https://github.com/ocaml/ocaml/issues/13252): Rework register assignment in the interpreter code on m68k on Linux, 
due to the %a5 register being used by GLIBC. 
(Miod Vallat, report by Stéphane Glondu, review by Gabriel Scherer and 
Xavier Leroy) 

- #13268(https://github.com/ocaml/ocaml/issues/13268): Fix a call to test in `configure.ac` that was causing errors when 
LDFLAGS contains several words. 
(Stéphane Glondu, review by Miod Vallat) 

- #13234(https://github.com/ocaml/ocaml/issues/13234), #13267(https://github.com/ocaml/ocaml/issues/13267): Open runtime events file in read-write mode on ARMel 
(ARMv5) systems due to atomic operations limitations on that 
platform. 
(Stéphane Glondu, review by Miod Vallat and Vincent Laviron) 

- #13188(https://github.com/ocaml/ocaml/issues/13188): fix races in the FFI code coming from the use of `Int_val(...)` 
on rooted values inside blocking questions / without the runtime lock. 
(Calling `Int_val(...)` on non-rooted immediates is fine, but any 
access to rooted values must be done outside blocking sections / 
with the runtime lock.) 
(Etienne Millon, review by Gabriel Scherer, Jan Midtgaard, Olivier Nicole) 

- #13318(https://github.com/ocaml/ocaml/issues/13318): Fix regression in GC alarms, and fix them for Flambda. 
(Guillaume Munch-Maccagnoni, report by Benjamin Monate, review by 
Vincent Laviron and Gabriel Scherer) 

- #13140(https://github.com/ocaml/ocaml/issues/13140): POWER back-end: fix issue with call to `caml_call_realloc_stack` 
from a DLL 
(Xavier Leroy, review by Miod Vallat) 

- #13370]https://github.com/ocaml/ocaml/issues/13370): Fix a low-probability crash when calling `Gc.counters`. 
(Demi Marie Obenour, review by Gabriel Scherer) 

- #13402(https://github.com/ocaml/ocaml/issues/13402), #13512(https://github.com/ocaml/ocaml/issues/13512), #13549(https://github.com/ocaml/ocaml/issues/13549), #13553(https://github.com/ocaml/ocaml/issues/13553): Revise bytecode implementation of callbacks 
so that it no longer produces dangling registered bytecode fragments. 
(Xavier Leroy, report by Jan Midtgaard, analysis by Stephen Dolan, 
review by Miod Vallat) 

- #13502(https://github.com/ocaml/ocaml/issues/13502): Fix misindexing related to `Gc.finalise_last` that could prevent 
finalisers from being run. 
(Nick Roberts, review by Mark Shinwell) 

- #13520(https://github.com/ocaml/ocaml/issues/13520): Fix compilation of native-code version of systhreads. Bytecode fields 
were being included in the thread descriptors. 
(David Allsopp, review by Sébastien Hinderer and Miod Vallat)