15254 %ymm registers not restored after signal handler
15367 x86 getfpregs() summons corrupting %xmm ghosts
15333 want x86 /proc xregs support (libc_db, libproc, mdb, etc.)
15336 want libc functions for extended ucontext_t
15334 want ps_lwphandle-specific reg routines
15328 FPU_CW_INIT mistreats reserved bit
15335 i86pc fpu_subr.c isn't really platform-specific
15332 setcontext(2) isn't actually noreturn
15331 need <sys/stdalign.h>
Change-Id: I7060aa86042dfb989f77fc3323c065ea2eafa9ad
Conflicts:
    usr/src/uts/common/fs/proc/prcontrol.c
    usr/src/uts/intel/os/archdep.c
    usr/src/uts/intel/sys/ucontext.h
    usr/src/uts/intel/syscall/getcontext.c

*** 22,48 ****
--- 22,60 ----
  /*
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
+ /*
+  * Copyright 2023 Oxide Computer Company
+  */
+ 
  #include "lint.h"
  #include <sys/types.h>
  #include <sys/ucontext.h>
  #include <setjmp.h>
  #include <ucontext.h>
+ #include <strings.h>
+ #include <upanic.h>
  #include "sigjmp_struct.h"
  #include "libc.h"
  
  #pragma weak _siglongjmp = siglongjmp
  
  void
  siglongjmp(sigjmp_buf env, int val)
  {
+         const char *msg = "siglongjmp(): setcontext() returned";
          ucontext_t *ucp = SIGJMP2UCONTEXT(env);
  
          if (val)
                  ucp->uc_mcontext.gregs[REG_R0] = val;
          else
                  ucp->uc_mcontext.gregs[REG_R0] = 1;
  
+         /*
+          * While unlikely, it is possible that setcontext() may fail for some
+          * reason. If that happens, we will kill the process.
+          */
          (void) setcontext(ucp);
+         upanic(msg, strlen(msg) + 1);
  }