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

*** 29,38 ****
--- 29,42 ----
   *      Copyright (c) 1988 AT&T
   *        All Rights Reserved
   */
  
  /*
+  * Copyright 2023 Oxide Computer Company
+  */
+ 
+ /*
   * Establish the default settings for the floating-point state for a C language
   * program:
   *      rounding mode           -- round to nearest default by OS,
   *      exceptions enabled      -- all masked
   *      sticky bits             -- all clear by default by OS.
*** 46,79 ****
  
  #include        "lint.h"
  #include        <sys/types.h>
  #include        <sys/sysi86.h>  /* for SI86FPHW/SI86FPSTART definitions */
  #include        <sys/fp.h>      /* for FPU_CW_INIT and SSE_MXCSR_INIT */
  
  extern int      __fltrounds();
  
  int     _fp_hw;                 /* default: bss: 0 == no hardware */
  int     _sse_hw;                /* default: bss: 0 == no sse */
  int     __flt_rounds;           /* ANSI rounding mode */
  
  void
  __fpstart()
  {
          /*
           * query OS for HW status and ensure the x87 and (optional)
           * SSE control words are (will be) set correctly.
           */
          if ((_sse_hw = sysi86(SI86FPSTART,
              &_fp_hw, FPU_CW_INIT, SSE_MXCSR_INIT)) == -1) {
-                 extern void _putcw();
- 
                  /*
!                  * (fallback to old syscall on old kernels)
                   */
!                 _sse_hw = 0;
!                 (void) sysi86(SI86FPHW, &_fp_hw);
!                 _putcw(0x133f);
          }
  
          /*
           * At this point the x87 fp environment that has been (or more
           * hopefully, will be) established by the kernel is:
--- 50,86 ----
  
  #include        "lint.h"
  #include        <sys/types.h>
  #include        <sys/sysi86.h>  /* for SI86FPHW/SI86FPSTART definitions */
  #include        <sys/fp.h>      /* for FPU_CW_INIT and SSE_MXCSR_INIT */
+ #include        <upanic.h>
  
  extern int      __fltrounds();
  
  int     _fp_hw;                 /* default: bss: 0 == no hardware */
  int     _sse_hw;                /* default: bss: 0 == no sse */
  int     __flt_rounds;           /* ANSI rounding mode */
  
+ #define UPANIC_MSG      "32-bit FPU init failed!"
+ 
  void
  __fpstart()
  {
          /*
           * query OS for HW status and ensure the x87 and (optional)
           * SSE control words are (will be) set correctly.
           */
          if ((_sse_hw = sysi86(SI86FPSTART,
              &_fp_hw, FPU_CW_INIT, SSE_MXCSR_INIT)) == -1) {
                  /*
!                  * Because the system only supports a 64-bit kernel, the above
!                  * should always work (we assume it does in 64-bit libc). If it
!                  * should fail, we upanic. Note, because the FPU state is
!                  * unknown, we use a static message below and don't rely upon
!                  * strlen(), but rather constant time lengths.
                   */
!                 upanic(UPANIC_MSG, sizeof (UPANIC_MSG));
          }
  
          /*
           * At this point the x87 fp environment that has been (or more
           * hopefully, will be) established by the kernel is: