feat(libc): implement syslog and vsyslog

[johnmaia]

What

Implements syslog (NID s-e0hFe21FA) and vsyslog (NID rzvf5zicF88) in libc. Two of the homebrew titles in #1578 import syslog from libSceLibcInternal, which resolves through libc: ps5-opengl (PPSA99005) and ProsperoRadio (PPSA99001).

• Output: each message is written to stderr as [syslog:<priority>] <message>, under a lock and flushed, with a newline added when the message has none. This is the same convention sceKernelDebugOutText uses ([debug:<channel>]).
• Format and priority follow FreeBSD's vsyslog:
  • %m expands to the guest errno's message (FreeBSD numbering via strerror_r), with any % in it doubled, and %%m stays a literal %m.
  • Bits outside LOG_PRIMASK | LOG_FACMASK produce syslog: unknown facility/priority: <hex> and are then masked off.
  • A missing facility becomes LOG_USER.
  • errno is preserved.
• Formatting uses the same paths as vfprintf: SysV va_list on Linux and LibcDetail::FormatWindows on Windows.
• Recorded in TechnicalDebt: messages go to stderr instead of the console's system log, and openlog, setlogmask and closelog are not implemented, so identity, options and mask are not applied. Neither title imports them.

Tested

• New guest_syslog test, registered in ctest. It captures stderr and checks the exact output for:

  • plain formatting;
  • %m with errno 2, a literal %%m and %%;
  • unknown priority bits (0x10004, the warning line followed by the masked message);
  • the default facility;
  • an empty message.

  It also checks that errno is unchanged.

• Linux (Ubuntu 24.04.5, GCC 13.3) and Windows 11 (WinLibs GCC 15.2.0 r7): guest_syslog, guest_errors, guest_formatting and guest_filesystem pass.

• No title was run: both titles still have other missing imports listed in Four open-source homebrew titles stop at start-up on unresolved imports (sysctl, pthread_set_name_np, isatty, mkstemp, signal sets, Opus decoders) #1578.

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 in TechnicalDebt
• 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: none
• AI-assisted: yes

🤖 Generated with Claude Code

[github-actions]

Progress report (54f28f2 → 9d1ac90)

📈 System libraries: 85.31% (+0.01%, +2 implemented functions)

✅ 2 implemented

Library	Name
libc	syslog_nid_postfix
libc	vsyslog_nid_postfix

[github-actions]

Other open pull requests touch the same code. Merging one will break the other, or both implement the same thing. If this one builds on them, list them in Depends on.

Pull request	Conflicting files (lines on main)	Same exports	Same new files
#1727		__error_nid_postfix
#1738		__error_nid_postfix
#1772		__error_nid_postfix
#1831	docs/dev/TechnicalDebt.md L362
#1860		__error_nid_postfix
#2051		__error_nid_postfix
#2057	core/libs/prx/libc/CMakeLists.txt L235
#2123		__error_nid_postfix

[adriadam10]

Checked build + full ctest on Linux (guest_syslog passes and fails without the change), and %m/%%/facility handling against FreeBSD lib/libc/gen/syslog.c; the Windows relinker failure is the runner's clang lacking the amdgcn target, unrelated to this PR.

One fix added as a separate commit on your branch:

• FreeBSD reports the "unknown facility/priority" complaint through syslog(LOG_ERR|LOG_CONS|LOG_PERROR|LOG_PID, ...), so the priority it logs is 0x23, not 3. Syslog.cpp, the test expectation ([syslog:35]) and the TechnicalDebt line now say so.

Not verified here: Windows runtime of the formatting path and any title. Merging once CI is green.