--- old/usr/src/lib/libc/i386/gen/makectxt.c
          +++ new/usr/src/lib/libc/i386/gen/makectxt.c

   1    1  /*
   2    2   * CDDL HEADER START
   3    3   *
   4    4   * The contents of this file are subject to the terms of the
   5    5   * Common Development and Distribution License (the "License").
   6    6   * You may not use this file except in compliance with the License.
   7    7   *
   8    8   * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9    9   * or http://www.opensolaris.org/os/licensing.
  10   10   * See the License for the specific language governing permissions
  11   11   * and limitations under the License.
  12   12   *
  13   13   * When distributing Covered Code, include this CDDL HEADER in each
  14   14   * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15   15   * If applicable, add the following below this CDDL HEADER, with the
  16   16   * fields enclosed by brackets "[]" replaced with your own identifying
  17   17   * information: Portions Copyright [yyyy] [name of copyright owner]
  18   18   *
  19   19   * CDDL HEADER END
  20   20   */
  21   21  
  22   22  /*
  23   23   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  24   24   * Use is subject to license terms.
  25   25   */
  26   26  
  27   27  /*      Copyright (c) 1988 AT&T */
  28   28  /*        All Rights Reserved   */
  29   29  
  30   30  /*
  31   31   * Copyright 2023 Oxide Computer Company
  32   32   */
  33   33  
  34   34  #pragma weak _makecontext = makecontext
  35   35  
  36   36  #include "lint.h"
  37   37  #include <stdarg.h>
  38   38  #include <ucontext.h>
  39   39  #include <sys/stack.h>
  40   40  #include <sys/auxv.h>
  41   41  #include <errno.h>
  42   42  #include "libc.h"
  43   43  
  44   44  /*
  45   45   * The ucontext_t that the user passes in must have been primed with a
  46   46   * call to getcontext(2), have the uc_stack member set to reflect the
  47   47   * stack which this context will use, and have the uc_link member set
  48   48   * to the context which should be resumed when this context returns.
  49   49   * When makecontext() returns, the ucontext_t will be set to run the
  50   50   * given function with the given parameters on the stack specified by
  51   51   * uc_stack, and which will return to the ucontext_t specified by uc_link.
  52   52   */
  53   53  
  54   54  /*
  55   55   * The original i386 ABI said that the stack pointer need be only 4-byte
  56   56   * aligned before a function call (STACK_ALIGN == 4).  The ABI supplement
  57   57   * version 1.0 changed the required alignment to 16-byte for the benefit of
  58   58   * floating point code compiled using sse2.  The compiler assumes this
  59   59   * alignment and maintains it for calls it generates.  If the stack is
  60   60   * initially properly aligned, it will continue to be so aligned.  If it is
  61   61   * not initially so aligned, it will never become so aligned.
  62   62   *
  63   63   * One slightly confusing detail to keep in mind is that the 16-byte
  64   64   * alignment (%esp & 0xf == 0) is true just *before* the call instruction.
  65   65   * The call instruction will then push a return value, decrementing %esp by
  66   66   * 4.  Therefore, if one dumps %esp at the at the very first instruction in
  67   67   * a function, it will end with a 0xc.  The compiler expects this and
  68   68   * compensates for it properly.
  69   69   *
  70   70   * Note: If you change this value, you need to change it in the following
  71   71   * files as well:
  72   72   *
  73   73   *  - lib/libc/i386/threads/machdep.c
  74   74   *  - lib/crt/i386/crti.s
  75   75   *  - lib/crt/i386/crt1.s
  76   76   */
  77   77  #undef  STACK_ALIGN
  78   78  #define STACK_ALIGN     16
  79   79  
  80   80  static void resumecontext(void);
  81   81  
  82   82  void
  83   83  makecontext(ucontext_t *ucp, void (*func)(), int argc, ...)
  84   84  {
  85   85          long *sp;
  86   86          long *tsp;
  87   87          va_list ap;
  88   88          size_t size;
  89   89  
  90   90          ucp->uc_mcontext.gregs[EIP] = (greg_t)func;
  91   91  
  92   92          size = sizeof (long) * (argc + 1);
  93   93  
  94   94          tsp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
  95   95              ucp->uc_stack.ss_size - size) & ~(STACK_ALIGN - 1));
  96   96  
  97   97          /*
  98   98           * Since we're emulating the call instruction, we must push the
  99   99           * return address (which involves adjusting the stack pointer to
 100  100           * have the proper 4-byte bias).
 101  101           */
 102  102          sp = tsp - 1;
 103  103  
 104  104          *sp = (long)resumecontext;              /* return address */
 105  105  
 106  106          ucp->uc_mcontext.gregs[UESP] = (greg_t)sp;
 107  107  
 108  108          /*
 109  109           * "push" all the arguments
 110  110           */
 111  111          va_start(ap, argc);
 112  112          while (argc-- > 0)
 113  113                  *tsp++ = va_arg(ap, long);
 114  114          va_end(ap);
 115  115  }
 116  116  
 117  117  
 118  118  static void
 119  119  resumecontext(void)
 120  120  {
 121  121          ucontext_t uc;
 122  122  
 123  123          (void) getcontext(&uc);
 124  124          (void) setcontext(uc.uc_link);
 125  125  }
 126  126  
 127  127  /*
 128  128   * This is the ISA-specific allocation logic for allocating and setting up an
 129  129   * extended ucontext_t. In particular, right now we need to allocate and add
 130  130   * space for the UC_XSAVE member if we have the appropriate hardware support.
 131  131   * The i386 / amd64 versions could be consolidated in a single x86 impl, but we
 132  132   * don't have that right now.
 133  133   */
 134  134  ucontext_t *
 135  135  ucontext_alloc(uint32_t flags)
 136  136  {
 137  137          boolean_t do_xsave = B_FALSE;
 138  138          size_t to_alloc = sizeof (ucontext_t);
 139  139          ucontext_t *ucp;
 140  140  
 141  141          if (flags != 0) {
 142  142                  errno = EINVAL;
 143  143                  return (NULL);
 144  144          }
 145  145  
 146  146          /*
 147  147           * This value isn't really 100% accurate. The xsave size is basically
 148  148           * the worst case that we can have. The XMM / xsave structures aren't
 149  149           * included in here, but are going to be enough to cover this. We can
 150  150           * probably try to do a little better and should consider asking the
 151  151           * kernel for something more accurate. In particular, the problem with
 152  152           * tis is that it doesn't account for the right size of future-looking
 153  153           * dynamic things, but then again neither does rtld. We'll deal with
 154  154           * this when we have support for the xfd MSR and actually use it. For
 155  155           * more information see uts/intel/os/fpu.c's big theory statement.
 156  156           */
 157  157          switch (___getauxval(AT_SUN_FPTYPE)) {
 158  158          case AT_386_FPINFO_XSAVE:
 159  159          case AT_386_FPINFO_XSAVE_AMD:
 160  160                  do_xsave = B_TRUE;
 161  161                  to_alloc += ___getauxval(AT_SUN_FPSIZE);
 162  162                  break;
 163  163          default:
 164  164                  break;
 165  165          }
 166  166  
 167  167          ucp = calloc(1, to_alloc);
 168  168          if (ucp == NULL) {
 169  169                  return (NULL);
 170  170          }
 171  171  
 172  172          if (do_xsave) {
 173  173                  uintptr_t addr = (uintptr_t)ucp;
 174  174                  ucp->uc_xsave = addr + sizeof (ucontext_t);
 175  175          }
 176  176  
 177  177          return (ucp);
 178  178  }
 179  179  
 180  180  void
 181  181  ucontext_free(ucontext_t *ucp)
 182  182  {
 183  183          free(ucp);
 184  184  }

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