Hi all,
This patch fixes a bug in the reserve_at function which caused it to
sometimes reserve space needed by the dll it was supposed to help land.
This happens when the dll tries to land in a free region which overlaps
the desired location. The new code exploits the image introspection
(patch #2) to get the dll's image size and avoids the corner cases.
Ryan
diff --git a/dll_init.cc b/dll_init.cc
--- a/dll_init.cc
+++ b/dll_init.cc
@@ -164,6 +164,7 @@ dll_list::alloc (HINSTANCE h, per_proces
d->handle = h;
d->has_dtors = true;
d->p = p;
+ d->image_size = ((pefile*)h)->optional_hdr ()->SizeOfImage;
d->ndeps = 0;
d->deps = NULL;
d->modname = wcsrchr (d->name, L'\\');
@@ -407,21 +408,33 @@ release_upto (const PWCHAR name, DWORD h
}
}
-/* Mark one page at "here" as reserved. This may force
- Windows NT to load a DLL elsewhere. */
+/* Reserve the chunk of free address space starting _here_ and (usually)
+ covering at least _dll_size_ bytes. However, we must take care not
+ to clobber the dll's target address range because it often overlaps.
+ */
static DWORD
-reserve_at (const PWCHAR name, DWORD here)
+reserve_at (const PWCHAR name, DWORD here, DWORD dll_base, DWORD dll_size)
{
DWORD size;
MEMORY_BASIC_INFORMATION mb;
if (!VirtualQuery ((void *) here, &mb, sizeof (mb)))
- size = 64 * 1024;
-
+ api_fatal ("couldn't examine memory at %08lx while mapping %W, %E",
+ here, name);
if (mb.State != MEM_FREE)
return 0;
size = mb.RegionSize;
+
+ // don't clobber the space where we want the dll to land
+ DWORD end = here + size;
+ DWORD dll_end = dll_base + dll_size;
+ if (dll_base < here && dll_end > here)
+ here = dll_end; // the dll straddles our left edge
+ else if (dll_base >= here && dll_base < end)
+ end = dll_base; // the dll overlaps partly or fully to our right
+
+ size = end - here;
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);
@@ -499,7 +512,8 @@ dll_list::load_after_fork (HANDLE parent
can in the child, due to differences in the load ordering.
Block memory at it's preferred address and try again. */
if ((DWORD) h > (DWORD) d->handle)
- preferred_block = reserve_at (d->name, (DWORD) h);
+ preferred_block = reserve_at (d->name, (DWORD) h,
+ (DWORD) d->handle, d->image_size);
}
}
diff --git a/dll_init.h b/dll_init.h
--- a/dll_init.h
+++ b/dll_init.h
@@ -52,6 +52,7 @@ struct dll
int count;
bool has_dtors;
dll_type type;
+ DWORD image_size;
long ndeps;
dll** deps;
PWCHAR modname;
* dll_init.cc (dll_list::alloc): initialize dll::image_size.
(reserve_at): no longer reserves space needed by the target dll if
the latter overlaps the free region to be blocked.
(dll_list::load_after_fork): use new version of reserve_at.
* dll_init.h (struct dll): add new members to track dll size.
