libc/winsup/cygwin/init.cc

/* init.cc

   Copyright 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
   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 <stdlib.h>
#include "thread.h"
#include "perprocess.h"
#include "cygtls.h"
#include "pinfo.h"
#include <ntdef.h>
#include "ntdll.h"

int NO_COPY dynamically_loaded;
static char *search_for = (char *) cygthread::stub;
unsigned threadfunc_ix[8] __attribute__((section (".cygwin_dll_common"), shared));
DWORD tls_func;

HANDLE sync_startup;

#define OLDFUNC_OFFSET -1

static void WINAPI
threadfunc_fe (VOID *arg)
{
  (void)__builtin_return_address(1);
  asm volatile ("andl $-16,%%esp" ::: "%esp");
  _cygtls::call ((DWORD (*)  (void *, void *)) (((char **) _tlsbase)[OLDFUNC_OFFSET]), arg);
}

static DWORD WINAPI
calibration_thread (VOID *arg)
{
  ExitThread (0);
}

static DWORD calibration_id;

/* We need to know where the OS stores the address of the thread function
   on the stack so that we can intercept the call and insert some tls
   stuff on the stack.  This function starts a known calibration thread.
   When it starts, a call will be made to dll_entry which will call munge_threadfunc
   looking for the calibration thread offset on the stack.  This offset will
   be stored and used by all executing cygwin processes. */
static void
prime_threads ()
{
  if (threadfunc_ix[0])
    sync_startup = INVALID_HANDLE_VALUE;
  else
    {
      search_for = (char *) calibration_thread;
      sync_startup = CreateThread (NULL, 0, calibration_thread, 0, 0, &calibration_id);
    }
}

/* If possible, redirect the thread entry point to a cygwin routine which
   adds tls stuff to the stack. */
static void
munge_threadfunc ()
{
  int i;
  char **ebp = (char **) __builtin_frame_address (0);
  if (!threadfunc_ix[0])
    {
      char **peb;
      char **top = (char **) _tlsbase;
      for (peb = ebp, i = 0; peb < top && i < 7; peb++)
	if (*peb == search_for)
	  threadfunc_ix[i++] = peb - ebp;
      if (0 && !threadfunc_ix[0])
	{
	  try_to_debug ();
	  return;
	}
    }

  char *threadfunc = ebp[threadfunc_ix[0]];
  if (threadfunc == (char *) calibration_thread)
    /* no need for the overhead */;
  else if (threadfunc_ix[0])
    {
      for (i = 0; threadfunc_ix[i]; i++)
	ebp[threadfunc_ix[i]] = (char *) threadfunc_fe;
      ((char **) _tlsbase)[OLDFUNC_OFFSET] = threadfunc;
    }
}

inline static void
respawn_wow64_process ()
{
  NTSTATUS ret;
  PROCESS_BASIC_INFORMATION pbi;
  HANDLE parent;

  BOOL is_wow64_proc = TRUE;	/* Opt on the safe side. */

  /* Unfortunately there's no simpler way to retrieve the
     parent process in NT, as far as I know.  Hints welcome. */
  ret = NtQueryInformationProcess (GetCurrentProcess (),
				   ProcessBasicInformation,
				   (PVOID) &pbi,
				   sizeof pbi, NULL);
  if (ret == STATUS_SUCCESS
      && (parent = OpenProcess (PROCESS_QUERY_INFORMATION,
				FALSE,
				pbi.InheritedFromUniqueProcessId)))
    {
      IsWow64Process (parent, &is_wow64_proc);
      CloseHandle (parent);
    }

  /* The parent is a real 64 bit process?  Respawn! */
  if (!is_wow64_proc)
    {
      PROCESS_INFORMATION pi;
      STARTUPINFO si;
      GetStartupInfo (&si);
      if (!CreateProcessA (NULL, GetCommandLineA (), NULL, NULL, TRUE,
			   CREATE_DEFAULT_ERROR_MODE
			   | GetPriorityClass (GetCurrentProcess ()),
			   NULL, NULL, &si, &pi))
	api_fatal ("Failed to create process <%s>, %E", GetCommandLineA ());
      CloseHandle (pi.hThread);
      if (WaitForSingleObject (pi.hProcess, INFINITE) == WAIT_FAILED)
	api_fatal ("Waiting for process %d failed, %E", pi.dwProcessId);
      CloseHandle (pi.hProcess);
      ExitProcess (0);
    }
}

extern void __stdcall dll_crt0_0 ();

HMODULE NO_COPY cygwin_hmodule;

extern "C" BOOL WINAPI
dll_entry (HANDLE h, DWORD reason, void *static_load)
{
  BOOL is_wow64_proc = FALSE;
  // _STRACE_ON;

  switch (reason)
    {
    case DLL_PROCESS_ATTACH:
      cygwin_hmodule = (HMODULE) h;
      dynamically_loaded = (static_load == NULL);

      /* Is the stack at an unusual address?  This is, an address which
	 is in the usual space occupied by the process image, but below
	 the auto load address of DLLs?
	 Check if we're running in WOW64 on a 64 bit machine *and* are
	 spawned by a genuine 64 bit process.  If so, respawn. */
      if (&is_wow64_proc >= (PBOOL) 0x400000
	  && &is_wow64_proc <= (PBOOL) 0x10000000
	  && IsWow64Process (GetCurrentProcess (), &is_wow64_proc)
	  && is_wow64_proc)
	respawn_wow64_process ();

      dll_crt0_0 ();
      prime_threads ();	// this should be the last thing to happen
      break;
    case DLL_PROCESS_DETACH:
      break;
    case DLL_THREAD_ATTACH:
      if (!sync_startup || GetCurrentThreadId () == calibration_id)
	munge_threadfunc ();
      break;
    case DLL_THREAD_DETACH:
      if (!sync_startup)
	_my_tls.remove (0);
      break;
    }

  return TRUE;
}