1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 
  22 /*
  23  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  24  * Use is subject to license terms.
  25  */
  26 
  27 /*
  28  *      Copyright (c) 1990, 1991 UNIX System Laboratories, Inc.
  29  *      Copyright (c) 1988 AT&T
  30  *        All Rights Reserved
  31  */
  32 
  33 /*
  34  * Copyright 2023 Oxide Computer Company
  35  */
  36 
  37 /*
  38  * Establish the default settings for the floating-point state for a C language
  39  * program:
  40  *      rounding mode           -- round to nearest default by OS,
  41  *      exceptions enabled      -- all masked
  42  *      sticky bits             -- all clear by default by OS.
  43  *      precision control       -- double extended
  44  * Set _fp_hw according to what floating-point hardware is available.
  45  * Set _sse_hw according to what SSE hardware is available.
  46  * Set __flt_rounds according to the rounding mode.
  47  */
  48 
  49 #pragma weak _fpstart = __fpstart
  50 
  51 #include        "lint.h"
  52 #include        <sys/types.h>
  53 #include        <sys/sysi86.h>    /* for SI86FPHW/SI86FPSTART definitions */
  54 #include        <sys/fp.h>        /* for FPU_CW_INIT and SSE_MXCSR_INIT */
  55 #include        <upanic.h>
  56 
  57 extern int      __fltrounds();
  58 
  59 int     _fp_hw;                 /* default: bss: 0 == no hardware */
  60 int     _sse_hw;                /* default: bss: 0 == no sse */
  61 int     __flt_rounds;           /* ANSI rounding mode */
  62 
  63 #define UPANIC_MSG      "32-bit FPU init failed!"
  64 
  65 void
  66 __fpstart()
  67 {
  68         /*
  69          * query OS for HW status and ensure the x87 and (optional)
  70          * SSE control words are (will be) set correctly.
  71          */
  72         if ((_sse_hw = sysi86(SI86FPSTART,
  73             &_fp_hw, FPU_CW_INIT, SSE_MXCSR_INIT)) == -1) {
  74                 /*
  75                  * Because the system only supports a 64-bit kernel, the above
  76                  * should always work (we assume it does in 64-bit libc). If it
  77                  * should fail, we upanic. Note, because the FPU state is
  78                  * unknown, we use a static message below and don't rely upon
  79                  * strlen(), but rather constant time lengths.
  80                  */
  81                 upanic(UPANIC_MSG, sizeof (UPANIC_MSG));
  82         }
  83 
  84         /*
  85          * At this point the x87 fp environment that has been (or more
  86          * hopefully, will be) established by the kernel is:
  87          *
  88          * affine infinity      0x1000
  89          * round to nearest     0x0000
  90          * 64-bit doubles       0x0300
  91          * precision, underflow, overflow, zero-divide, denorm, invalid masked
  92          *                      0x003f
  93          *
  94          * which conforms to the 4th edition i386 ABI definition.
  95          *
  96          * Additionally, if we have SSE hardware, we've also masked all
  97          * the same traps, and have round to nearest.
  98          */
  99 
 100         __flt_rounds = 1;       /* ANSI way of saying round-to-nearest */
 101 }