newlib-cygwin/winsup/cygwin/miscfuncs.cc

/* miscfuncs.cc: misc funcs that don't belong anywhere else

   Copyright 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004,
   2005, 2006, 2007, 2008, 2009, 2010, 2011 Red Hat, Inc.

This file is part of Cygwin.

This software is a copyrighted work licensed under the terms of the
Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
details. */

#include "winsup.h"
#include "miscfuncs.h"
#include <sys/uio.h>
#include <assert.h>
#include <alloca.h>
#include <limits.h>
#include <sys/param.h>
#include <wchar.h>
#include <wingdi.h>
#include <winuser.h>
#include <winnls.h>
#include "cygtls.h"
#include "ntdll.h"
#include "path.h"
#include "fhandler.h"
#include "dtable.h"
#include "cygheap.h"
#include "pinfo.h"
#include "exception.h"

long tls_ix = -1;

const char case_folded_lower[] NO_COPY = {
   0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,  15,
  16,  17,  18,  19,  20,  21,  22,  23,  24,  25,  26,  27,  28,  29,  30,  31,
  32, '!', '"', '#', '$', '%', '&',  39, '(', ')', '*', '+', ',', '-', '.', '/',
 '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?',
 '@', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '[',  92, ']', '^', '_',
 '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '{', '|', '}', '~', 127,
 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143,
 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159,
 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175,
 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191,
 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207,
 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223,
 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239,
 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255
};

const char case_folded_upper[] NO_COPY = {
   0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,  15,
  16,  17,  18,  19,  20,  21,  22,  23,  24,  25,  26,  27,  28,  29,  30,  31,
  32, '!', '"', '#', '$', '%', '&',  39, '(', ')', '*', '+', ',', '-', '.', '/',
 '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?',
 '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[',  92, ']', '^', '_',
 '`', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '{', '|', '}', '~', 127,
 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143,
 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159,
 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175,
 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191,
 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207,
 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223,
 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239,
 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255
};

const char isalpha_array[] NO_COPY = {
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,
0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,   0,   0,   0,   0,   0,
   0,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,
0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,0x20,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0
};

extern "C" int __stdcall
cygwin_wcscasecmp (const wchar_t *ws, const wchar_t *wt)
{
  UNICODE_STRING us, ut;

  RtlInitUnicodeString (&us, ws);
  RtlInitUnicodeString (&ut, wt);
  return RtlCompareUnicodeString (&us, &ut, TRUE);
}

extern "C" int __stdcall
cygwin_wcsncasecmp (const wchar_t  *ws, const wchar_t *wt, size_t n)
{
  UNICODE_STRING us, ut;
  size_t ls = 0, lt = 0;

  while (ws[ls] && ls < n)
    ++ls;
  RtlInitCountedUnicodeString (&us, ws, ls * sizeof (WCHAR));
  while (wt[lt] && lt < n)
    ++lt;
  RtlInitCountedUnicodeString (&ut, wt, lt * sizeof (WCHAR));
  return RtlCompareUnicodeString (&us, &ut, TRUE);
}

extern "C" int __stdcall
cygwin_strcasecmp (const char *cs, const char *ct)
{
  UNICODE_STRING us, ut;
  ULONG len;

  len = (strlen (cs) + 1) * sizeof (WCHAR);
  RtlInitEmptyUnicodeString (&us, (PWCHAR) alloca (len), len);
  us.Length = sys_mbstowcs (us.Buffer, us.MaximumLength, cs) * sizeof (WCHAR);
  len = (strlen (ct) + 1) * sizeof (WCHAR);
  RtlInitEmptyUnicodeString (&ut, (PWCHAR) alloca (len), len);
  ut.Length = sys_mbstowcs (ut.Buffer, ut.MaximumLength, ct) * sizeof (WCHAR);
  return RtlCompareUnicodeString (&us, &ut, TRUE);
}

extern "C" int __stdcall
cygwin_strncasecmp (const char *cs, const char *ct, size_t n)
{
  UNICODE_STRING us, ut;
  ULONG len;
  size_t ls = 0, lt = 0;

  while (cs[ls] && ls < n)
    ++ls;
  len = (ls + 1) * sizeof (WCHAR);
  RtlInitEmptyUnicodeString (&us, (PWCHAR) alloca (len), len);
  us.Length = sys_mbstowcs (us.Buffer, ls + 1, cs, ls) * sizeof (WCHAR);
  while (ct[lt] && lt < n)
    ++lt;
  len = (lt + 1) * sizeof (WCHAR);
  RtlInitEmptyUnicodeString (&ut, (PWCHAR) alloca (len), len);
  ut.Length = sys_mbstowcs (ut.Buffer, lt + 1, ct, lt)  * sizeof (WCHAR);
  return RtlCompareUnicodeString (&us, &ut, TRUE);
}

extern "C" char * __stdcall
cygwin_strlwr (char *string)
{
  UNICODE_STRING us;
  size_t len = (strlen (string) + 1) * sizeof (WCHAR);

  us.MaximumLength = len; us.Buffer = (PWCHAR) alloca (len);
  us.Length = sys_mbstowcs (us.Buffer, len, string) * sizeof (WCHAR)
	      - sizeof (WCHAR);
  RtlDowncaseUnicodeString (&us, &us, FALSE);
  sys_wcstombs (string, len / sizeof (WCHAR), us.Buffer);
  return string;
}

extern "C" char * __stdcall
cygwin_strupr (char *string)
{
  UNICODE_STRING us;
  size_t len = (strlen (string) + 1) * sizeof (WCHAR);

  us.MaximumLength = len; us.Buffer = (PWCHAR) alloca (len);
  us.Length = sys_mbstowcs (us.Buffer, len, string) * sizeof (WCHAR)
	      - sizeof (WCHAR);
  RtlUpcaseUnicodeString (&us, &us, FALSE);
  sys_wcstombs (string, len / sizeof (WCHAR), us.Buffer);
  return string;
}

int __stdcall
check_invalid_virtual_addr (const void *s, unsigned sz)
{
  MEMORY_BASIC_INFORMATION mbuf;
  const void *end;

  for (end = (char *) s + sz; s < end;
       s = (char *) mbuf.BaseAddress + mbuf.RegionSize)
    if (!VirtualQuery (s, &mbuf, sizeof mbuf))
      return EINVAL;
  return 0;
}

static char __attribute__ ((noinline))
dummytest (volatile char *p)
{
  return *p;
}

ssize_t
check_iovec (const struct iovec *iov, int iovcnt, bool forwrite)
{
  if (iovcnt <= 0 || iovcnt > IOV_MAX)
    {
      set_errno (EINVAL);
      return -1;
    }

  myfault efault;
  if (efault.faulted (EFAULT))
    return -1;

  size_t tot = 0;

  while (iovcnt != 0)
    {
      if (iov->iov_len > SSIZE_MAX || (tot += iov->iov_len) > SSIZE_MAX)
	{
	  set_errno (EINVAL);
	  return -1;
	}

      volatile char *p = ((char *) iov->iov_base) + iov->iov_len - 1;
      if (!iov->iov_len)
	/* nothing to do */;
      else if (!forwrite)
	*p  = dummytest (p);
      else
	dummytest (p);

      iov++;
      iovcnt--;
    }

  assert (tot <= SSIZE_MAX);

  return (ssize_t) tot;
}

/* Try hard to schedule another thread. */
void
yield ()
{
  int prio = GetThreadPriority (GetCurrentThread ());
  SetThreadPriority (GetCurrentThread (), THREAD_PRIORITY_IDLE);
  for (int i = 0; i < 2; i++)
    {
      /* MSDN implies that SleepEx(0,...) will force scheduling of other
	 threads.  Unlike SwitchToThread() the documentation does not mention
	 other cpus so, presumably (hah!), this + using a lower priority will
	 stall this thread temporarily and cause another to run.  */
      SleepEx (0, false);
    }
  SetThreadPriority (GetCurrentThread (), prio);
}

/* Get a default value for the nice factor.  When changing these values,
   have a look into the below function nice_to_winprio.  The values must
   match the layout of the static "priority" array. */
int
winprio_to_nice (DWORD prio)
{
  switch (prio)
    {
      case REALTIME_PRIORITY_CLASS:
	return -20;
      case HIGH_PRIORITY_CLASS:
	return -16;
      case ABOVE_NORMAL_PRIORITY_CLASS:
	return -8;
      case NORMAL_PRIORITY_CLASS:
	return 0;
      case BELOW_NORMAL_PRIORITY_CLASS:
	return 8;
      case IDLE_PRIORITY_CLASS:
	return 16;
    }
  return 0;
}

/* Get a Win32 priority matching the incoming nice factor.  The incoming
   nice is limited to the interval [-NZERO,NZERO-1]. */
DWORD
nice_to_winprio (int &nice)
{
  static const DWORD priority[] NO_COPY =
    {
      REALTIME_PRIORITY_CLASS,		/*  0 */
      HIGH_PRIORITY_CLASS,		/*  1 */
      HIGH_PRIORITY_CLASS,
      HIGH_PRIORITY_CLASS,
      HIGH_PRIORITY_CLASS,
      HIGH_PRIORITY_CLASS,
      HIGH_PRIORITY_CLASS,
      HIGH_PRIORITY_CLASS,		/*  7 */
      ABOVE_NORMAL_PRIORITY_CLASS,	/*  8 */
      ABOVE_NORMAL_PRIORITY_CLASS,
      ABOVE_NORMAL_PRIORITY_CLASS,
      ABOVE_NORMAL_PRIORITY_CLASS,
      ABOVE_NORMAL_PRIORITY_CLASS,
      ABOVE_NORMAL_PRIORITY_CLASS,
      ABOVE_NORMAL_PRIORITY_CLASS,
      ABOVE_NORMAL_PRIORITY_CLASS,	/* 15 */
      NORMAL_PRIORITY_CLASS,		/* 16 */
      NORMAL_PRIORITY_CLASS,
      NORMAL_PRIORITY_CLASS,
      NORMAL_PRIORITY_CLASS,
      NORMAL_PRIORITY_CLASS,
      NORMAL_PRIORITY_CLASS,
      NORMAL_PRIORITY_CLASS,
      NORMAL_PRIORITY_CLASS,		/* 23 */
      BELOW_NORMAL_PRIORITY_CLASS,	/* 24 */
      BELOW_NORMAL_PRIORITY_CLASS,
      BELOW_NORMAL_PRIORITY_CLASS,
      BELOW_NORMAL_PRIORITY_CLASS,
      BELOW_NORMAL_PRIORITY_CLASS,
      BELOW_NORMAL_PRIORITY_CLASS,
      BELOW_NORMAL_PRIORITY_CLASS,
      BELOW_NORMAL_PRIORITY_CLASS,	/* 31 */
      IDLE_PRIORITY_CLASS,		/* 32 */
      IDLE_PRIORITY_CLASS,
      IDLE_PRIORITY_CLASS,
      IDLE_PRIORITY_CLASS,
      IDLE_PRIORITY_CLASS,
      IDLE_PRIORITY_CLASS,
      IDLE_PRIORITY_CLASS,
      IDLE_PRIORITY_CLASS		/* 39 */
    };
  if (nice < -NZERO)
    nice = -NZERO;
  else if (nice > NZERO - 1)
    nice = NZERO - 1;
  DWORD prio = priority[nice + NZERO];
  return prio;
}

#undef CreatePipe
bool
create_pipe (PHANDLE hr,PHANDLE hw, LPSECURITY_ATTRIBUTES sa, DWORD n)
{
  for (int i = 0; i < 10; i++)
    if (CreatePipe (hr, hw, sa, n))
      return true;
    else if (GetLastError () == ERROR_PIPE_BUSY && i < 9)
      Sleep (10);
    else
      break;
  return false;
}

/* backslashify: Convert all forward slashes in src path to back slashes
   in dst path.  Add a trailing slash to dst when trailing_slash_p arg
   is set to 1. */

void
backslashify (const char *src, char *dst, bool trailing_slash_p)
{
  const char *start = src;

  while (*src)
    {
      if (*src == '/')
	*dst++ = '\\';
      else
	*dst++ = *src;
      ++src;
    }
  if (trailing_slash_p
      && src > start
      && !isdirsep (src[-1]))
    *dst++ = '\\';
  *dst++ = 0;
}

/* slashify: Convert all back slashes in src path to forward slashes
   in dst path.  Add a trailing slash to dst when trailing_slash_p arg
   is set to 1. */

void
slashify (const char *src, char *dst, bool trailing_slash_p)
{
  const char *start = src;

  while (*src)
    {
      if (*src == '\\')
	*dst++ = '/';
      else
	*dst++ = *src;
      ++src;
    }
  if (trailing_slash_p
      && src > start
      && !isdirsep (src[-1]))
    *dst++ = '/';
  *dst++ = 0;
}

/* CygwinCreateThread.

   Replacement function for CreateThread.  What we do here is to remove
   parameters we don't use and instead to add parameters we need to make
   the function pthreads compatible. */

struct thread_wrapper_arg
{
  LPTHREAD_START_ROUTINE func;
  PVOID arg;
  char *stackaddr;
  char *stackbase;
  char *commitaddr;
};

DWORD WINAPI
thread_wrapper (VOID *arg)
{
  /* Just plain paranoia. */
  if (!arg)
    return ERROR_INVALID_PARAMETER;

  /* Fetch thread wrapper info and free from cygheap. */
  thread_wrapper_arg wrapper_arg = *(thread_wrapper_arg *) arg;
  cfree (arg);

  /* Remove _cygtls from this stack since it won't be used anymore. */
  _my_tls.remove (0);

  /* Set stack values in TEB */
  PTEB teb = NtCurrentTeb ();
  teb->Tib.StackBase = wrapper_arg.stackbase;
  teb->Tib.StackLimit = wrapper_arg.commitaddr ?: wrapper_arg.stackaddr;
  /* Set DeallocationStack value.  If we have an application-provided stack,
     we set DeallocationStack to NULL, so NtTerminateThread does not deallocate
     any stack.  If we created the stack in CygwinCreateThread, we set
     DeallocationStack to the stackaddr of our own stack, so it's automatically
     deallocated when the thread is terminated. */
  char *dealloc_addr = (char *) teb->DeallocationStack;
  teb->DeallocationStack = wrapper_arg.commitaddr ? wrapper_arg.stackaddr
						  : NULL;
  /* Store the OS-provided DeallocationStack address in wrapper_arg.stackaddr.
     The below assembler code will release the OS stack after switching to our
     new stack. */
  wrapper_arg.stackaddr = dealloc_addr;

  /* Initialize new _cygtls. */
  _my_tls.init_thread (wrapper_arg.stackbase - CYGTLS_PADSIZE,
		       (DWORD (*)(void*, void*)) wrapper_arg.func);

  /* Copy exception list over to new stack.  I'm not quite sure how the
     exception list is extended by Windows itself.  What's clear is that it
     always grows downwards and that it starts right at the stackbase.
     Therefore we first count the number of exception records and place
     the copy at the stackbase, too, so there's still a lot of room to
     extend the list up to where our _cygtls region starts. */
  _exception_list *old_start = (_exception_list *) teb->Tib.ExceptionList;
  unsigned count = 0;
  teb->Tib.ExceptionList = NULL;
  for (_exception_list *e_ptr = old_start;
       e_ptr && e_ptr != (_exception_list *) -1;
       e_ptr = e_ptr->prev)
    ++count;
  if (count)
    {
      _exception_list *new_start = (_exception_list *) wrapper_arg.stackbase
						       - count;
      teb->Tib.ExceptionList = (struct _EXCEPTION_REGISTRATION_RECORD *)
			       new_start;
      while (true)
	{
	  new_start->handler = old_start->handler;
	  if (old_start->prev == (_exception_list *) -1)
	    {
	      new_start->prev = (_exception_list *) -1;
	      break;
	    }
	  new_start->prev = new_start + 1;
	  new_start = new_start->prev;
	  old_start = old_start->prev;
	}
    }

  __asm__ ("\n\
	   movl  %[WRAPPER_ARG], %%ebx # Load &wrapper_arg into ebx  \n\
	   movl  (%%ebx), %%eax        # Load thread func into eax   \n\
	   movl  4(%%ebx), %%ecx       # Load thread arg into ecx    \n\
	   movl  8(%%ebx), %%edx       # Load stackaddr into edx     \n\
	   movl  12(%%ebx), %%ebx      # Load stackbase into ebx     \n\
	   subl  %[CYGTLS], %%ebx      # Subtract CYGTLS_PADSIZE     \n\
	   subl  $4, %%ebx             # Subtract another 4 bytes    \n\
	   movl  %%ebx, %%esp          # Set esp                     \n\
	   xorl  %%ebp, %%ebp          # Set ebp to 0                \n\
	   # Now we moved to the new stack.  Save thread func address\n\
	   # and thread arg on new stack                             \n\
	   pushl %%ecx                 # Push thread arg onto stack  \n\
	   pushl %%eax                 # Push thread func onto stack \n\
	   # Now it's safe to release the OS stack.                  \n\
	   pushl $0x8000               # dwFreeType: MEM_RELEASE     \n\
	   pushl $0x0                  # dwSize:     0               \n\
	   pushl %%edx                 # lpAddress:  stackaddr       \n\
	   call _VirtualFree@12        # Shoot                       \n\
	   # All set.  We can pop the thread function address from   \n\
	   # the stack and call it.  The thread arg is still on the  \n\
	   # stack in the expected spot.                             \n\
	   popl  %%eax                 # Pop thread_func address     \n\
	   call  *%%eax                # Call thread func            \n"
	   : : [WRAPPER_ARG] "r" (&wrapper_arg),
	       [CYGTLS] "i" (CYGTLS_PADSIZE));
  /* Never return from here. */
  ExitThread (0);
}

/* FIXME: This should be settable via setrlimit (RLIMIT_STACK). */
#define DEFAULT_STACKSIZE (512 * 1024)

HANDLE WINAPI
CygwinCreateThread (LPTHREAD_START_ROUTINE thread_func, PVOID thread_arg,
		    PVOID stackaddr, ULONG stacksize, ULONG guardsize,
		    DWORD creation_flags, LPDWORD thread_id)
{
  PVOID real_stackaddr = NULL;
  ULONG real_stacksize = 0;
  ULONG real_guardsize = 0;
  thread_wrapper_arg *wrapper_arg;
  HANDLE thread = NULL;

  wrapper_arg = (thread_wrapper_arg *) ccalloc (HEAP_STR, 1,
						sizeof *wrapper_arg);
  if (!wrapper_arg)
    {
      SetLastError (ERROR_OUTOFMEMORY);
      return NULL;
    }
  wrapper_arg->func = thread_func;
  wrapper_arg->arg = thread_arg;

  /* Set stacksize. */
  real_stacksize = stacksize ?: DEFAULT_STACKSIZE;
  if (real_stacksize < PTHREAD_STACK_MIN)
    real_stacksize = PTHREAD_STACK_MIN;
  if (stackaddr)
    {
      /* If the application provided the stack, just use it. */
      wrapper_arg->stackaddr = (char *) stackaddr;
      wrapper_arg->stackbase = (char *) stackaddr + real_stacksize;
    }
  else
    {
      /* If not, we have to create the stack here. */
      real_stacksize = roundup2 (real_stacksize, wincap.page_size ());
      /* If no guardsize has been specified by the application, use the
	 system pagesize as default. */
      real_guardsize = (guardsize != (ULONG) -1)
		       ? guardsize : wincap.page_size ();
      if (real_guardsize)
	real_guardsize = roundup2 (real_guardsize, wincap.page_size ());
      /* Add the guardsize to the stacksize, but only if the stacksize and
	 the guardsize have been explicitely specified. */
      if (stacksize || guardsize != (ULONG) -1)
	real_stacksize += real_guardsize;
      /* Now roundup the result to the next allocation boundary. */
      real_stacksize = roundup2 (real_stacksize,
				 wincap.allocation_granularity ());
      /* Reserve stack.
	 FIXME? If the TOP_DOWN method tends to collide too much with
	 other stuff, we should provide our own mechanism to find a
	 suitable place for the stack.  Top down from the start of
	 the Cygwin DLL comes to mind. */
      real_stackaddr = VirtualAlloc (NULL, real_stacksize,
				     MEM_RESERVE | MEM_TOP_DOWN,
				     PAGE_EXECUTE_READWRITE);
      if (!real_stackaddr)
	return NULL;
      /* Set up committed region.  In contrast to the OS we commit 64K and
	 set up just a single guard page at the end. */
      char *commitaddr = (char *) real_stackaddr
				  + real_stacksize
				  - wincap.allocation_granularity ();
      if (!VirtualAlloc (commitaddr, wincap.page_size (), MEM_COMMIT,
			 PAGE_EXECUTE_READWRITE | PAGE_GUARD))
	goto err;
      commitaddr += wincap.page_size ();
      if (!VirtualAlloc (commitaddr, wincap.allocation_granularity ()
				     - wincap.page_size (), MEM_COMMIT,
			 PAGE_EXECUTE_READWRITE))
	goto err;
      if (real_guardsize)
	VirtualAlloc (real_stackaddr, real_guardsize, MEM_COMMIT,
		      PAGE_NOACCESS);
      wrapper_arg->stackaddr = (char *) real_stackaddr;
      wrapper_arg->stackbase = (char *) real_stackaddr + real_stacksize;
      wrapper_arg->commitaddr = commitaddr;
    }
  /* Use the STACK_SIZE_PARAM_IS_A_RESERVATION parameter so only the
     minimum size for a thread stack is reserved by the OS.  This doesn't
     work on Windows 2000, but we deallocate the OS stack in thread_wrapper
     anyway, so this should be a problem only in a tight memory condition.
     Note that we reserve a 256K stack, not 64K, otherwise the thread creation
     might crash the process due to a stack overflow. */
  thread = CreateThread (&sec_none_nih, 4 * PTHREAD_STACK_MIN,
			 thread_wrapper, wrapper_arg,
			 creation_flags | STACK_SIZE_PARAM_IS_A_RESERVATION,
			 thread_id);

err:
  if (!thread && real_stackaddr)
    {
      /* Don't report the wrong error even though VirtualFree is very unlikely
	 to fail. */
      DWORD err = GetLastError ();
      VirtualFree (real_stackaddr, 0, MEM_RELEASE);
      SetLastError (err);
    }
  return thread;
}