[MarcZX10]

What

Carry Hussein Kadhim's raise(0) fix onto current main, preserving his original commit author. Signal zero is now treated as a thread-validity check: it returns 0 without touching dispositions, blocked/pending state, handlers or errno. Other out-of-range values still return EINVAL.

Tested

• Linux: built guest_signal_tests, guest_kill_tests and guest_sigtimedwait_tests.
• Linux: guest_signals, guest_kill and guest_sigtimedwait passed (3/3).
• Linux: python3 tools/check_conventions.py --base upstream/main passed.
• No GPU or game runtime tests apply.
• The Windows checks are reported in issue libkernel: raise(0) returns EINVAL where FreeBSD treats signal 0 as a validity check and returns 0; fix branch ready #5257; I did not run them locally.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed under Silent stubs in their library's technical debt file
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: fix(libkernel): keep the signal mask per thread #3986 (it changes the same raise implementation; this fix should layer on its per-thread signal behavior)
• Unblocks: none
• GPUs tested: n/a
• AI-assisted: yes

[xXPBSXx]

Windows 10 (19045), MinGW-w64 GCC 15.2.0, Release, -j4: head 57655db38 of this PR merged onto main d7bb2fee3 (clean merge, 2 files).

• guest_signals passes (1.55 s, ctest).
• With core/libs/prx/libkernel/System/src/Signals.cpp taken back to main and the PR's new test lines kept, guest_signals fails (exit code 0xc0000409).
• Not run: Linux, a console, a title.

AI-assisted (Claude Code).

[oneandonlydean]

Closing: no title is known to reach this. With the queue at 700+ open PRs, please hold off on new PRs that don't name a title needing the change until it's down. If a title stops on this on current main, reopen with the title ID and the log line.