cpu/native: fix lockup on libucontext

[maribu]

Contribution description

The setcontext() implementation of glibc does restore the signal mask to the target thread during the switch, libucontext does not

Instead, we just manually enable signals again just before the call to setcontext().

With this, tests like tests/core/mutex_canel or tests/core/irq now pass on native64 when using libucontext.

Testing procedure

Run

make BOARD=native64 -C tests/core/irq
make BOARD=native64 -C tests/core/mutex_cancel 

On master e.g. using Alpine Linux

git:(master) ~/Repos/software/RIOT/master ➜ make BOARD=native64 flash test -j -C tests/core/irq         
make: Entering directory '/home/maribu/Repos/software/RIOT/master/tests/core/irq'
Building application "tests_irq" for "native64" with CPU "native".
[...]
RIOT native interrupts/signals initialized.
TZ not set, setting UTC
RIOT native64 board initialized.
RIOT native hardware initialization complete.

main(): This is RIOT! (Version: 2026.01-devel-164-gb8c553)
START
busy_thread created
xtimer_wait()
busy_thread starting
Timeout in expect script at "child.expect('SUCCESS')" (tests/core/irq/tests/01-run.py:9)

make: *** [/home/maribu/Repos/software/RIOT/master/makefiles/tests/tests.inc.mk:32: test] Error 1
make: Leaving directory '/home/maribu/Repos/software/RIOT/master/tests/core/irq'

git:(master) ~/Repos/software/RIOT/master ➜ make BOARD=native64 flash test -j -C tests/core/mutex_cancel
make: Entering directory '/home/maribu/Repos/software/RIOT/master/tests/core/mutex_cancel'
Building application "tests_mutex_cancel" for "native64" with CPU "native".
[...]
RIOT native interrupts/signals initialized.
TZ not set, setting UTC
RIOT native64 board initialized.
RIOT native hardware initialization complete.

main(): This is RIOT! (Version: 2026.01-devel-164-gb8c553)
Test Application for mutex_cancel / mutex_lock_cancelable
=========================================================

Test without cancellation: OK
Test early cancellation: OK
Verify no side effects on subsequent calls: Timeout in expect script at "child.expect("TEST PASSED")" (tests/core/mutex_cancel/tests/01-run.py:16)

make: *** [/home/maribu/Repos/software/RIOT/master/makefiles/tests/tests.inc.mk:32: test] Error 1
make: Leaving directory '/home/maribu/Repos/software/RIOT/master/tests/core/mutex_cancel'

This PR

git:(cpu/native/libucontext/fix-lockup) ~/Repos/software/RIOT/master ➜ make BOARD=native64 flash test -j -C tests/core/irq
make: Entering directory '/home/maribu/Repos/software/RIOT/master/tests/core/irq'
Building application "tests_irq" for "native64" with CPU "native".
[...]
RIOT native interrupts/signals initialized.
TZ not set, setting UTC
RIOT native64 board initialized.
RIOT native hardware initialization complete.

main(): This is RIOT! (Version: 2026.01-devel-165-g8c44f-cpu/native/libucontext/fix-lockup)
START
busy_thread created
xtimer_wait()
busy_thread starting
main: return
{ "threads": [{ "name": "idle", "stack_size": 16384, "stack_used": 1048 }]}
{ "threads": [{ "name": "main", "stack_size": 20480, "stack_used": 2600 }]}
i: 119908691
j: 119908691
k: 119908691
SUCCESS
{ "threads": [{ "name": "busy_thread", "stack_size": 20480, "stack_used": 2552 }]}

Process already stopped
make: Leaving directory '/home/maribu/Repos/software/RIOT/master/tests/core/irq'

git:(cpu/native/libucontext/fix-lockup) ~/Repos/software/RIOT/master ➜ make BOARD=native64 flash test -j -C tests/core/mutex_cancel 
make: Entering directory '/home/maribu/Repos/software/RIOT/master/tests/core/mutex_cancel'
Building application "tests_mutex_cancel" for "native64" with CPU "native".
[...]
RIOT native interrupts/signals initialized.
TZ not set, setting UTC
RIOT native64 board initialized.
RIOT native hardware initialization complete.

main(): This is RIOT! (Version: 2026.01-devel-165-g8c44f-cpu/native/libucontext/fix-lockup)
Test Application for mutex_cancel / mutex_lock_cancelable
=========================================================

Test without cancellation: OK
Test early cancellation: OK
Verify no side effects on subsequent calls: OK
Test late cancellation: OK
TEST PASSED
{ "threads": [{ "name": "idle", "stack_size": 16384, "stack_used": 1296 }]}
{ "threads": [{ "name": "main", "stack_size": 20480, "stack_used": 2728 }]}

Process already stopped
make: Leaving directory '/home/maribu/Repos/software/RIOT/master/tests/core/mutex_cancel'

Issues/PRs references

None

[riot-ci]

Murdock results

✔️ PASSED

87af1a4 cpu/native: fix lockup on libucontext

Success	Failures	Total	Runtime
10932	0	10932	13m:14s

Artifacts

• Documentation preview

[mguetschow]

I have reproduced the bug with the patched tinybuild-native64 from RIOT-OS/riotdocker#259 (comment) using BUILD_IN_DOCKER=1 DOCKER_IMAGE=local/tinybuild-native64:latest make -C tests/core/irq all test.

With the changes from this PR applied, both this one and tests/core/mutex_cancel successfully complete.

Thanks for finding and fixing! I haven't looked much into the changes themselves though, being quite unfamiliar with native context switching, trusting your expertise here.

[maribu]

Thx ❤️