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

*** 22,31 ****
--- 22,35 ----
  /*
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
+ /*
+  * Copyright 2023 Oxide Computer Company
+  */
+ 
          .file   "__getcontext.s"
  
  /*
   * __getcontext() must be implemented in assembler, as opposed
   * to the other members of the SYS_context family (see ucontext.c)
*** 39,43 ****
--- 43,55 ----
          movq    $0, %rdi
          SYSTRAP_RVAL1(context)
          SYSCERROR
          RETC
          SET_SIZE(__getcontext)
+ 
+         ENTRY(__getcontext_extd)
+         movq    %rdi, %rsi
+         movq    $4, %rdi
+         SYSTRAP_RVAL1(context)
+         SYSCERROR
+         RETC
+         SET_SIZE(__getcontext_extd)