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

@@ -22,10 +22,14 @@
 /*
  * 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)

@@ -42,5 +46,16 @@
         popl    %edx
         movl    %edx, 0(%esp)
         SYSCERROR
         RET
         SET_SIZE(__getcontext)
+
+        ENTRY(__getcontext_extd)
+        popl    %edx
+        pushl   $4
+        pushl   %edx
+        SYSTRAP_RVAL1(context)
+        popl    %edx
+        movl    %edx, 0(%esp)
+        SYSCERROR
+        RET
+        SET_SIZE(__getcontext_extd)