2011-03-12  Jon TURNEY  <jon.turney@dronecode.org.uk>

	* dll_init.cc (reserve_at, release_at): New functions.
	(load_after_fork): Make a 3rd pass at trying to load the DLL in
	the right place.


Index: cygwin/dll_init.cc
===================================================================
--- cygwin/dll_init.cc.orig	2011-03-27 18:19:06.000000000 +0100
+++ cygwin/dll_init.cc	2011-03-28 23:43:47.125000000 +0100
@@ -254,15 +254,47 @@
       }
 }
 
+/* Mark one page at "here" as reserved.  This may force
+   Windows NT to load a DLL elsewhere. */
+static DWORD
+reserve_at (const PWCHAR name, DWORD here)
+{
+  DWORD size;
+  MEMORY_BASIC_INFORMATION mb;
+
+  if (!VirtualQuery ((void *) here, &mb, sizeof (mb)))
+    size = 64 * 1024;
+
+  if (mb.State != MEM_FREE)
+    return 0;
+
+  size = mb.RegionSize;
+  if (!VirtualAlloc ((void *) here, size, MEM_RESERVE, PAGE_NOACCESS))
+    api_fatal ("couldn't allocate memory %p(%d) for '%W' alignment, %E\n",
+               here, size, name);
+  return here;
+}
+
+/* Release the memory previously allocated by "reserve_at" above. */
+static void
+release_at (const PWCHAR name, DWORD here)
+{
+  if (!VirtualFree ((void *) here, 0, MEM_RELEASE))
+    api_fatal ("couldn't release memory %p for '%W' alignment, %E\n",
+               here, name);
+}
+
 /* Reload DLLs after a fork.  Iterates over the list of dynamically loaded
    DLLs and attempts to load them in the same place as they were loaded in the
    parent. */
 void
 dll_list::load_after_fork (HANDLE parent)
 {
+  DWORD preferred_block = 0;
+
   for (dll *d = &dlls.start; (d = d->next) != NULL; )
     if (d->type == DLL_LOAD)
-      for (int i = 0; i < 2; i++)
+      for (int i = 0; i < 3; i++)
 	{
 	  /* See if DLL will load in proper place.  If so, free it and reload
 	     it the right way.
@@ -281,15 +313,26 @@
 	      if (h == d->handle)
 		h = LoadLibraryW (d->name);
 	    }
-	  /* If we reached here on the second iteration of the for loop
+
+	  /* If we reached here on subsequent iterations of the for loop
 	     then there is a lot of memory to release. */
 	  if (i > 0)
 	    release_upto (d->name, (DWORD) d->handle);
+
+          /* If we reached here on the last iteration of the for loop
+             then there's a bit of memory to release */
+          if (i > 1)
+            {
+              if (preferred_block)
+                release_at(d->name, preferred_block);
+              preferred_block = 0;
+            }
+
 	  if (h == d->handle)
 	    break;		/* Success */
 
-	  if (i > 0)
-	    /* We tried once to relocate the dll and it failed. */
+	  if (i > 1)
+	    /* We tried to relocate the dll and it failed. */
 	    api_fatal ("unable to remap %W to same address as parent: %p != %p",
 		       d->name, d->handle, h);
 
@@ -299,6 +342,15 @@
 	     second DLL always loads into a different location. So, block all
 	     of the memory up to the new load address and try again. */
 	  reserve_upto (d->name, (DWORD) d->handle);
+
+          /* Dll *still* loaded in the wrong place.  This can happen if it
+             couldn't load at the preferred base in the parent, but can in
+             the child, due to ordering differences.  Block memory at it's
+             preferred address and try again. */
+          if (i > 0)
+            {
+              preferred_block = reserve_at(d->name, (DWORD)h);
+            }
 	}
   in_forkee = false;
 }