Add mes and mescc-tools-extra

mescc-tools-extra contains two important tools:
- cp
- chmod

mes first builds itself from a mes 0.21 seed as used by guix, and then
builds a mes 0.22 and then mes 0.22 using that created mes 0.22.

It does /not/ use bootstrap.sh as we don't have a proper shell at this
point, it has been manually adapted for kaem.

sysa/mes-0.22/lib/linux/signal.c

@@ -0,0 +1,72 @@
+/* -*-comment-start: "//";comment-end:""-*-
+ * GNU Mes --- Maxwell Equations of Software
+ * Copyright © 2018,2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+ *
+ * This file is part of GNU Mes.
+ *
+ * GNU Mes is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * GNU Mes is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Mes.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/syscall.h>
+#include <syscall.h>
+#include <unistd.h>
+#include <signal.h>
+
+#if __i386__
+#else
+void
+_restorer_for_siginfo (void)
+{
+  _sys_call (SYS_rt_sigreturn);
+}
+#endif
+
+sighandler_t
+signal (int signum, sighandler_t action)
+{
+#if __i386__
+  return _sys_call2 (SYS_signal, signum, action);
+#else
+  static struct sigaction setup_action = { 0 };
+  static struct sigaction old = { 0 };
+  unsigned short bitindex;
+  unsigned short itembitcount;
+
+  setup_action.sa_handler = action;
+  /* The sa_restorer is not used.  Reason:
+     * The kernel uses its own restorer anyway by pretending we gave one on
+     our side (no, really).
+     glibc still has a custom restorer because they want to be able to
+     backtrace.  gdb has a second part that detects a specific instruction
+     sequence and then fixes up the backtrace.  Since we don't use that
+     specific instruction sequence and also the non-siginfo restorer
+     is complicated (pops foreign item off the stack--so needs inline
+     assembly) and we don't support great debuggability in other places,
+     I've decided to take the easy way out for now. */
+  /*setup_action.sa_restorer = _restorer_for_siginfo;*/
+  bitindex = signum - 1;
+  itembitcount = 8 * sizeof(setup_action.sa_mask.items[0]);
+  setup_action.sa_mask.items[bitindex / itembitcount] = 1UL << (bitindex % itembitcount);
+  old.sa_handler = SIG_DFL;
+  setup_action.sa_flags = SA_RESTART;
+#if __x86_64__
+  /* Tell kernel that we use a restorer, on penalty of segfault.  */
+  setup_action.sa_flags |= SA_RESTORER;
+#endif
+  int r = _sys_call4 (SYS_rt_sigaction, signum, (long)&setup_action, (long)&old, sizeof (sigset_t));
+  if (r)
+    return 0;
+  return old.sa_handler;
+#endif
+}