* dll_init.cc (dll_list::alloc): Allocate memory using a section

	object.  Explain why.  Drop call to GetSystemInfo, rather call
	getpagesize to get allocation granularity.  Only align to allocation
	granularity under WOW64.  Use roundup2 to align.
	(dll_list::detach): Call NtUnmapViewOfSection instead of VirtualFree.

1 files changed, 64 insertions, 25 deletions

diff --git a/winsup/cygwin/dll_init.cc b/winsup/cygwin/dll_init.cc
index e42718d..5b026c7 100644
--- a/winsup/cygwin/dll_init.cc
+++ b/winsup/cygwin/dll_init.cc
@@ -21,6 +21,9 @@ details. */
 #include "cygtls.h"
 #include <wchar.h>
 #include <alloca.h>
+#include <unistd.h>
+#include <sys/param.h>
+#include "ntdll.h"
 
 extern void __stdcall check_sanity_and_sync (per_process *);
 
@@ -110,7 +113,6 @@ dll_list::alloc (HINSTANCE h, per_process *p, dll_type type)
 {
   WCHAR name[NT_MAX_PATH];
   DWORD namelen = GetModuleFileNameW (h, name, sizeof (name));
-  size_t d_size = sizeof (dll) + namelen * sizeof (WCHAR);
 
   /* Already loaded? */
   dll *d = dlls[name];
@@ -120,15 +122,18 @@ dll_list::alloc (HINSTANCE h, per_process *p, dll_type type)
       return d;		/* Return previously allocated pointer. */
     }
 
-  SYSTEM_INFO s1;
-  GetSystemInfo (&s1);
-
-  int i;
   void *s = p->bss_end;
-  DWORD n;
+  size_t d_size = sizeof (dll) + namelen * sizeof (WCHAR);
+
   MEMORY_BASIC_INFORMATION m;
+  NTSTATUS status = 0;
+  HANDLE sect_h;
+  OBJECT_ATTRIBUTES oa;
+  InitializeObjectAttributes (&oa, NULL, 0, NULL,
+			      sec_none.lpSecurityDescriptor);
+
   /* Search for space after the DLL */
-  for (i = 0; i <= RETRIES; i++, s = (char *) m.BaseAddress + m.RegionSize)
+  for (int i = 0; i <= RETRIES; i++, s = (char *) m.BaseAddress + m.RegionSize)
     {
       if (!VirtualQuery (s, &m, sizeof (m)))
 	return NULL;	/* Can't do it. */
@@ -138,30 +143,64 @@ dll_list::alloc (HINSTANCE h, per_process *p, dll_type type)
 	  if (i == RETRIES)
 	    return NULL;	/* Oh well.  Couldn't locate free space. */
 
-	  /* Ensure that this is rounded to the nearest page boundary.
-	     FIXME: Should this be ensured by VirtualQuery? */
-	  n = (DWORD) m.BaseAddress;
-	  DWORD r = n % s1.dwAllocationGranularity;
-
-	  if (r)
-	    n = ((n - r) + s1.dwAllocationGranularity);
+	  d = (dll *) m.BaseAddress;
+	  /* Instead of calling VirtualAlloc, which always allocates memory
+	     on a 64K boundary, we allocate the memory using a section
+	     object.  The disadvantage of the 64K boundary in this case is
+	     the fact that that boundary could be easily the start address
+	     of another DLL yet to load into memory.
+
+	     On x86, using a section object allows us to allocate the struct
+	     dll into a memory slot in the remainder of the last 64K slot of
+	     the DLL.  This memory slot will never be used for anything
+	     else.  Given that the struct dll will fit into a single page
+	     99.99% of the time anyway, this is a neat way to avoid DLL load
+	     address collisions in most cases.
+
+	     Of course, this doesn't help if the DLL needs all of the 64K
+	     memory slot but there's only a 1 in 16 chance for that.
+
+	     And, alas, it won't work on 64 bit systems because the
+	     AT_ROUND_TO_PAGE flag required to make a page-aligned allocation
+	     isn't supported under WOW64.  So, as with VirtualAlloc, ensure
+	     that address is rounded up to next 64K allocation boundary if
+	     running under WOW64. */
+	  if (wincap.is_wow64 ())
+	    d = (dll *) roundup2 ((uintptr_t) d, getpagesize ());
+
+	  LARGE_INTEGER so = { QuadPart: d_size };
+	  status = NtCreateSection (&sect_h, SECTION_ALL_ACCESS, &oa, &so,
+				    PAGE_READWRITE, SEC_COMMIT, NULL);
+	  if (NT_SUCCESS (status))
+	    {
+	      ULONG viewsize = 0;
+	      so.QuadPart = 0;
+	      status = NtMapViewOfSection (sect_h, GetCurrentProcess (),
+					   (void **) &d, 0, d_size, &so,
+					   &viewsize, ViewUnmap,
+					   wincap.is_wow64 ()
+					   ? 0 : AT_ROUND_TO_PAGE,
+					   PAGE_READWRITE);
+#ifdef DEBUGGING
+	      if (!NT_SUCCESS (status))
+		system_printf ("NtMapViewOfSection failed, %p", status);
+#endif
+	      NtClose (sect_h);
+	    }
+#ifdef DEBUGGING
+	  else
+	    system_printf ("NtCreateSection failed, %p", status);
+#endif
 
-	  /* First reserve the area of memory, then commit it. */
-	  if (VirtualAlloc ((void *) n, d_size, MEM_RESERVE, PAGE_READWRITE))
-	    d = (dll *) VirtualAlloc ((void *) n, d_size, MEM_COMMIT,
-				      PAGE_READWRITE);
-	  if (d)
+	  if (NT_SUCCESS (status))
 	    break;
 	}
     }
 
   /* Did we succeed? */
-  if (d == NULL)
+  if (!NT_SUCCESS (status))
     {			/* Nope. */
-#ifdef DEBUGGING
-      system_printf ("VirtualAlloc failed, %E");
-#endif
-      __seterrno ();
+      __seterrno_from_nt_status (status);
       return NULL;
     }
 
@@ -212,7 +251,7 @@ dll_list::detach (void *retaddr)
 	  loaded_dlls--;
 	if (end == d)
 	  end = d->prev;
-	VirtualFree (d, 0, MEM_RELEASE);
+	NtUnmapViewOfSection (GetCurrentProcess (), d);
 	break;
       }
 }