Add a libsys status report

website/content/en/status/report-2024-01-2024-03/libsys.adoc

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+=== libsys
+
+Contact: Brooks Davis <[email protected]>
+
+The libsys project removes direct system calls from `libc.so` and
+`libpthread.so` (aka `libthr.so`) to a separate `libsys.so`.
+This will:
+
+ * Isolate language runtimes from the details of system call implementations.
+ * Better support logging and replay frameworks for systems calls.
+ * Support elimination of the ability to make system calls outside trusted code in the runtime linker and `libsys`.
+
+This work was initially inspired by a compartmentalization prototype in CheriBSD in 2016.
+Ali Mashtizadeh and Tal Garfinkel picked that work up and attempted to upstream it (link:https://reviews.freebsd.org/D14609[D14609]).
+Unfortunately we couldn't figure out how to review and land the massive reorganization required through a phabricator review so it languished.
+Last year the CHERI project once again found a need for system call separation in a new library-based compartmentalization framework in CheriBSD so I rebuilt the patch from scratch, committing dozens of libc cleanups along the way.
+I landed the first batch of changes on February 5th.
+Since then I've made a number of refinements to the way we link libsys as well as which symbols are provided in which library.
+
+Thanks to Konstantin Belousov <[email protected]> for many rounds of review and feedback as well as runtime linker fixes.
+Thanks to Mark Johnston <[email protected]> for runtime linker debugging and Dimitry Andric <[email protected]> for sanitizer fixes.  
+Thanks also to everyone who reported bugs and helped debug issues.
+
+==== Known issues (as of the end of the reporting period)
+
+ * The `libsys` ABI is not yet considered stable (it's safe to assume `__sys_foo()` will be supported so language runtimes can use it now).
+ * Programs using the address sanitizer must be linked with `-lsys` (resolved in base at publication time).
+
+==== TODO
+
+ * Add a `libsys.h`.  (See link:https://reviews.freebsd.org/D44387[D44387] and other reviews in the stack.)
+ * Update man:intro[2] for `libsys`.
+ * Finalize the ABI.  I'm likely to reduce the set of `_` (underscore) prefixed symbols we expose.
+ * MFC the existence of `libsys`?  It's not clear this is practical, but it might be possible to MFC something useful for language runtimes.
+
+==== Help wanted
+
+ * Port language runtimes that don't use `libc` to use `libsys` for system calls rather than rolling their own interfaces.
+ * Explore limitations on where system calls can be made similar to OpenBSD's link:https://man.openbsd.org/OpenBSD-7.3/msyscall[msyscall(2)] (now obsolete) and link:https://man.openbsd.org/pinsyscalls[pinsyscalls(2)] (not an obvious match to our libsys).
+
+Sponsor: AFRL, DARPA