Cygwin: dlfcn: add native DLLs to dll list

If native DLLs are dlopen'ed, we have to keep track of the load
count, so dlclose doesn't misbehave.  We also have to keep track
for the sake of a forked child so the handle returned by dlopen
is still valid in the child.

To accomplish that, add a new type DLL_NATIVE.

Fixes: 82b31085f6ad ("Cygwin: dlfcn: avoid ENOENT on dlcose after dlopen(cygwin1.dll)")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

4 files changed, 55 insertions, 19 deletions

diff --git a/winsup/cygwin/dlfcn.cc b/winsup/cygwin/dlfcn.cc
index fdcbb51..f029ebb 100644
--- a/winsup/cygwin/dlfcn.cc
+++ b/winsup/cygwin/dlfcn.cc
@@ -284,6 +284,16 @@ dlopen (const char *name, int flags)
 	      else
 		++d->count;
 	    }
+	  else
+	    {
+	      /* All Cygwin DLLs loaded or linked into this process get a dll
+	         record when they call dll_dllcrt0 on init.  So if we don't
+		 find the dll it's a native DLL.  Add it as DLL_NATIVE.
+		 Simply restore the LoadLibrary count after fork.  Don't care
+		 where they are loaded to, don't try to fix up their data and
+		 bss segments after fork, and don't run dtors. */
+	      dlls.alloc ((HMODULE) ret, user_data, DLL_NATIVE);
+	    }
 	}
 
       if (ret && nodelete)
@@ -364,6 +374,10 @@ dlclose (void *handle)
       else if (d->count != INT_MIN)
 	{
 	  --d->count;
+	  /* Native DLLs don't call cygwin_detach_dll so they have to be
+	     detached explicitely. */
+	  if (d->type == DLL_NATIVE && d->count <= 0)
+	    dlls.detach (handle);
 	  if (!FreeLibrary ((HMODULE) handle))
 	    {
 	      __seterrno ();
diff --git a/winsup/cygwin/dll_init.cc b/winsup/cygwin/dll_init.cc
index aab11d1..b8f38b5 100644
--- a/winsup/cygwin/dll_init.cc
+++ b/winsup/cygwin/dll_init.cc
@@ -314,7 +314,8 @@ dll_list::alloc (HINSTANCE h, per_process *p, dll_type type)
   /* Already loaded?  For linked DLLs, only compare the basenames.  Linked
      DLLs are loaded using just the basename and the default DLL search path.
      The Windows loader picks up the first one it finds.
-     This also applies to cygwin1.dll and the main-executable (DLL_SELF).
+     This also applies to cygwin1.dll and the main-executable (DLL_SELF)
+     and native DLLs (DLL_NATIVE).
      When in_load_after_fork, dynamically loaded dll's are reloaded
      using their parent's forkable_ntname, if available.  */
   dll *d = (type != DLL_LOAD) ? dlls.find_by_modname (modname) :
@@ -346,7 +347,6 @@ dll_list::alloc (HINSTANCE h, per_process *p, dll_type type)
     {
       size_t forkntsize = forkable_ntnamesize (type, ntname, modname);
 
-      /* FIXME: Change this to new at some point. */
       d = (dll *) cmalloc (HEAP_2_DLL, sizeof (*d)
 			   + ((ntnamelen + forkntsize) * sizeof (*ntname)));
 
@@ -356,14 +356,20 @@ dll_list::alloc (HINSTANCE h, per_process *p, dll_type type)
       d->modname = d->ntname + (modname - ntname);
       d->handle = h;
       d->count = 0;	/* Reference counting performed in dlopen/dlclose. */
-      /* DLL_SELF dtors (main-executable, cygwin1.dll) are run elsewhere */
-      d->has_dtors = type != DLL_SELF;
+      /* DLL_SELF dtors (main-executable, cygwin1.dll) are run elsewhere,
+         DLL_NATIVE dtors whereever native DLLs do it. */
+      d->has_dtors = (type == DLL_LINK || type == DLL_LOAD);
       d->p = p;
       d->ndeps = 0;
       d->deps = NULL;
       d->image_size = ((pefile*)h)->optional_hdr ()->SizeOfImage;
       d->preferred_base = (void*) ((pefile*)h)->optional_hdr()->ImageBase;
       d->type = type;
+      if (type == DLL_NATIVE)
+	{
+	  d->count = 1;
+	  reload_on_fork = 1;
+	}
       d->fii.IndexNumber.QuadPart = -1LL;
       if (!forkntsize)
 	d->forkable_ntname = NULL;
@@ -541,8 +547,10 @@ dll_list::topsort_visit (dll* d, bool seek_tail)
 }
 
 
+/* If called from dlopen/dlclose, from_dlfcn is true and we return any dll if
+   the address matches.  Otherwise we only want DLL_LINK and DLL_LOAD dlls. */
 dll *
-dll_list::find (void *retaddr, bool find_self)
+dll_list::find (void *retaddr, bool from_dlfcn)
 {
   MEMORY_BASIC_INFORMATION m;
   if (!VirtualQuery (retaddr, &m, sizeof m))
@@ -551,7 +559,8 @@ dll_list::find (void *retaddr, bool find_self)
 
   dll *d = &start;
   while ((d = d->next))
-    if ((d->type != DLL_SELF || find_self) && d->handle == h)
+    if ((from_dlfcn || d->type == DLL_LINK || d->type == DLL_LOAD)
+        && d->handle == h)
       break;
   return d;
 }
@@ -569,12 +578,16 @@ dll_list::detach (void *retaddr)
   guard (true);
   if ((d = find (retaddr)))
     {
-      /* Ensure our exception handler is enabled for destructors */
-      exception protect;
-      /* Call finalize function if we are not already exiting */
-      if (!exit_state)
-	__cxa_finalize (d->handle);
-      d->run_dtors ();
+      /* Only run dtors for Cygwin DLLs. */
+      if (d->type == DLL_LINK || d->type == DLL_LOAD)
+	{
+	  /* Ensure our exception handler is enabled for destructors */
+	  exception protect;
+	  /* Call finalize function if we are not already exiting */
+	  if (!exit_state)
+	    __cxa_finalize (d->handle);
+	  d->run_dtors ();
+	}
       d->prev->next = d->next;
       if (d->next)
 	d->next->prev = d->prev;
@@ -596,8 +609,9 @@ dll_list::init ()
   /* Walk the dll chain, initializing each dll */
   dll *d = &start;
   dll_global_dtors_recorded = d->next != NULL;
+  /* Init linked and early loaded Cygwin DLLs. */
   while ((d = d->next))
-    if (d->type != DLL_SELF) /* linked and early loaded dlls */
+    if (d->type == DLL_LINK || d->type == DLL_LOAD)
       d->init ();
 }
 
@@ -684,7 +698,10 @@ dll_list::load_after_fork (HANDLE parent)
 
   in_load_after_fork = true;
   if (reload_on_fork)
-    load_after_fork_impl (parent, dlls.istart (DLL_LOAD), 0);
+    {
+      load_after_fork_impl (parent, dlls.istart (DLL_NATIVE), 0);
+      load_after_fork_impl (parent, dlls.istart (DLL_LOAD), 0);
+    }
   track_self ();
   in_load_after_fork = false;
 }
@@ -709,7 +726,7 @@ void dll_list::load_after_fork_impl (HANDLE parent, dll* d, int retries)
      the LoadLibraryExW call unconditional.
    */
   for ( ; d; d = dlls.inext ())
-    if (d->handle != d->preferred_base)
+    if (hold_type == DLL_LOAD && d->handle != d->preferred_base)
       {
 	/* See if the DLL will load in proper place. If not, unload it,
 	   reserve the memory around it, and try again.
@@ -757,9 +774,11 @@ void dll_list::load_after_fork_impl (HANDLE parent, dll* d, int retries)
      interim mapping (for rebased dlls) . The dll list is sorted in
      dependency order, so we shouldn't pull in any additional dlls
      outside our control.  */
-  for (dll *d = dlls.istart (DLL_LOAD); d; d = dlls.inext ())
+  for (dll *d = dlls.istart (hold_type); d; d = dlls.inext ())
     {
-      if (d->handle == d->preferred_base)
+      if (hold_type == DLL_NATIVE)
+	/* just LoadLibrary... */;
+      else if (d->handle == d->preferred_base)
 	{
 	  if (!VirtualFree (d->handle, 0, MEM_RELEASE))
 	    fabort ("unable to release protective reservation for %W (%p), %E",
diff --git a/winsup/cygwin/local_includes/dll_init.h b/winsup/cygwin/local_includes/dll_init.h
index f79b157..4b76a74 100644
--- a/winsup/cygwin/local_includes/dll_init.h
+++ b/winsup/cygwin/local_includes/dll_init.h
@@ -34,7 +34,9 @@ struct per_module
 typedef enum
 {
   DLL_NONE,
-  DLL_SELF, /* main-program.exe, cygwin1.dll */
+  DLL_SELF,	/* main-program.exe, cygwin1.dll */
+  DLL_NATIVE,	/* dlopen'ed native DLLs.  reload after fork, but otherwise
+		   do nothing, just as with DLL_SELF. */
   DLL_LINK,
   DLL_LOAD,
   DLL_ANY
diff --git a/winsup/cygwin/release/3.6.1 b/winsup/cygwin/release/3.6.1
index 491d7dc..07a29ec 100644
--- a/winsup/cygwin/release/3.6.1
+++ b/winsup/cygwin/release/3.6.1
@@ -16,7 +16,8 @@ Fixes:
   stack area is not accessible from the signal handler.
   Addresses: https://cygwin.com/pipermail/cygwin/2025-March/257714.html
 
-- Fix reference counting when dlopen/dlclose is called on the Cygwin DLL.
+- Fix reference counting when dlopen/dlclose is called on the Cygwin DLL
+  or on non-Cygwin DLLs.
   Addresses: https://cygwin.com/pipermail/cygwin/2025-March/257783.html
 
 - Fix reference counting when dlopen/dlclose a DLL with RTLD_NODELETE.