Re: Protection errors on Mac OS X 10.6 (Snow Leopard)

[Abdulaziz Ghuloum <aghuloum at gmail dot com>]

On Sep 8, 2009, at 12:55 AM, Andrew Haley wrote:

> Sure, its overkill, but it'll still work.

There are stuff from <mntent.h> that's not available on darwin, so,
it seems like we can only mmap.

> > > Go into closures.c, find the definition of FFI_MMAP_EXEC_WRIT for
> > > your system, and set it accordingly.
> >
> > I can do that on my computer, yes.  But what about people who
> > use my program that depends on libffi?  I cannot expect them to
> > have to patch and recompile libffi just to use my program, right?
>
> Try it.  If it works, we can check it in.  The alternative is to write
> a bunch of special case code for Snow Leopard.  I'm happy either
> way; your call.


I tried this patch (against 3.0.8) and after running the autotools,
reconfiguring, and building, it seems to work for my system (Ikarus
Scheme <http://ikarus-scheme.org/>).  Basically, in closure.c, all
the stuff about temporary files is used iff FFI_MMAP_EXEC_SELINUX is
set (not darwin) or else dlmmap would just do mmap and return the
pointer (unchecked).  Also, configure.ac sets FFI_MMAP_EXEC_WRIT
explicitly on darwin10, making it go through the mmap-only path.

Let me know if this is good enough (or not).

Aziz,,,

=== modified file 'configure.ac'
--- configure.ac	2009-09-07 22:56:10 +0000
+++ configure.ac	2009-09-07 22:57:36 +0000
@@ -260,6 +260,16 @@
     fi
 fi

+case "$target" in
+  i?86-apple-darwin10*)
+    AC_DEFINE(FFI_MMAP_EXEC_WRIT, 1,
+              [Cannot use malloc on this target, so, we revert to
+               alternative means])
+    ;;
+esac
+
+
+
 AC_CACHE_CHECK([whether .eh_frame section should be read-only],
     libffi_cv_ro_eh_frame, [
 	libffi_cv_ro_eh_frame=no

=== modified file 'src/closures.c'
--- src/closures.c	2009-09-07 22:56:10 +0000
+++ src/closures.c	2009-09-07 23:08:05 +0000
@@ -93,7 +93,6 @@
 #include <unistd.h>
 #include <string.h>
 #include <stdio.h>
-#include <mntent.h>
 #include <sys/param.h>
 #include <pthread.h>

@@ -105,6 +104,7 @@
 #if FFI_MMAP_EXEC_SELINUX
 #include <sys/statfs.h>
 #include <stdlib.h>
+#include <mntent.h>

 static int selinux_enabled = -1;

@@ -180,6 +180,7 @@
 #undef mmap
 #undef munmap

+#if FFI_MMAP_EXEC_SELINUX
 /* A mutex used to synchronize access to *exec* variables in this  
file.  */
 static pthread_mutex_t open_temp_exec_file_mutex =  
PTHREAD_MUTEX_INITIALIZER;

@@ -444,6 +445,27 @@

   return dlmmap_locked (start, length, prot, flags, offset);
 }
+#else
+
+static void *
+dlmmap (void *start, size_t length, int prot,
+	int flags, int fd, off_t offset)
+{
+
+  assert (start == NULL && length % malloc_getpagesize == 0
+	  && prot == (PROT_READ | PROT_WRITE)
+	  && flags == (MAP_PRIVATE | MAP_ANONYMOUS)
+	  && fd == -1 && offset == 0);
+
+#if FFI_CLOSURE_TEST
+  printf ("mapping in %zi\n", length);
+#endif
+
+  return mmap (start, length, prot | PROT_EXEC, flags, fd, offset);
+}
+
+#endif
+

 /* Release memory at the given address, as well as the corresponding
    executable page if it's separate.  */