Would an increase to PTHREAD_KEYS_MAX be an example of a FreeBSD ABI change? (lang/rust involved in why I ask)

Would an increase to PTHREAD_KEYS_MAX be an example of a FreeBSD ABI change?


Why I ask: an active failure for at least rust use on armv7 . . .

The armv7 1.94.0 rust-bootstrap used to try to build 1.95.0 of lang/rust
for armv7 gets the Thread Local Storage failure "Out of TLS keys".

The same was true for the armv7 1.93.0 rust-bootstrap used to try to
build the armv7 1.94.0:

<https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294545>
(Robert Clausecker, not me.)


OpenBSD increased PTHREAD_KEYS_MAX to 512 to avoid getting such "Out of
TLS keys" failures, not necessarily for armv7 or for building rustc:

<https://github.com/openbsd/src/commit/f90c65410264d8346b711e36bca7ee1f0dde5ca9>
(2025-11-11)

QUOTE from OpenBSD's commit:
bump PTHREAD_KEYS_MAX to 512
the rust libstd emutls version is using one pthread_key per
thread-variable. it means the maximum number of thread-variable at a
time is PTHREAD_KEYS_MAX.

with recent rustc 1.91.0, we start hiting the limit while compiling some
programs (like sysutils/rustic).

ok robert@
"Let's go 512 and hope someone eventually does proper TLS" deraadt@
END QUOTE

I think they had 256 previous to the change, not just 128.

(The "libstd emutls version" may not be always involved for rust's
context? Also: the failure type is apparently not limited to building
the rust compiler/toolchain. The overall issue is not FreeBSD OS specific.)


Note: It appears that the official FreeBSD port-package building for
armv7 stopped shortly before this started to be an issue. That is why
fallout reports have not been accumulating for the "out of TLS keys" issue.


If increasing PTHREAD_KEYS_MAX is an ABI change, an implication is that
14.*-RELEASE and 15.*-RELEASE could not be changed, possibly eliminating
rust use on armv7 going forward.


Note:
It is my understanding that alternate Thread Local Storage models for
rust require use of rust-nightly (unstable) builds instead of stable
rust builds.


-- 
===
Mark Millard
marklmi at yahoo.com