Document requirements for calling mmcheck to install corruption checking

hooks and set up to enforce the requirements.  However, we still allow
unconditional installation until some complications are resolved.

1 files changed, 208 insertions, 0 deletions

diff --git a/mmalloc/attach.c b/mmalloc/attach.c
new file mode 100644
index 0000000..44fff4f
--- /dev/null
+++ b/mmalloc/attach.c
@@ -0,0 +1,208 @@
+/* Initialization for access to a mmap'd malloc managed region.
+   Copyright 1992 Free Software Foundation, Inc.
+
+   Contributed by Fred Fish at Cygnus Support.   fnf@cygnus.com
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include "mmalloc.h"
+
+#ifndef SEEK_SET
+#define SEEK_SET 0
+#endif
+
+/* Forward declarations/prototypes for local functions */
+
+static struct mdesc *reuse PARAMS ((int));
+
+/* Initialize access to a mmalloc managed region.
+
+   If FD is a valid file descriptor for an open file then data for the
+   mmalloc managed region is mapped to that file, otherwise "/dev/zero"
+   is used and the data will not exist in any filesystem object.
+
+   If the open file corresponding to FD is from a previous use of
+   mmalloc and passes some basic sanity checks to ensure that it is
+   compatible with the current mmalloc package, then it's data is
+   mapped in and is immediately accessible at the same addresses in
+   the current process as the process that created the file.
+
+   If BASEADDR is not NULL, the mapping is established starting at the
+   specified address in the process address space.  If BASEADDR is NULL,
+   the mmalloc package chooses a suitable address at which to start the
+   mapped region, which will be the value of the previous mapping if
+   opening an existing file which was previously built by mmalloc, or
+   for new files will be a value chosen by mmap.
+
+   Specifying BASEADDR provides more control over where the regions
+   start and how big they can be before bumping into existing mapped
+   regions or future mapped regions.
+
+   On success, returns a "malloc descriptor" which is used in subsequent
+   calls to other mmalloc package functions.  It is explicitly "void *"
+   ("char *" for systems that don't fully support void) so that users
+   of the package don't have to worry about the actual implementation
+   details.
+
+   On failure returns NULL. */
+
+
+#if defined(HAVE_MMAP)
+
+PTR
+mmalloc_attach (fd, baseaddr)
+  int fd;
+  PTR baseaddr;
+{
+  struct mdesc mtemp;
+  struct mdesc *mdp;
+  PTR mbase;
+  struct stat sbuf;
+
+  /* First check to see if FD is a valid file descriptor, and if so, see
+     if the file has any current contents (size > 0).  If it does, then
+     attempt to reuse the file.  If we can't reuse the file, either
+     because it isn't a valid mmalloc produced file, was produced by an
+     obsolete version, or any other reason, then we fail to attach to
+     this file. */
+
+  if (fd >= 0)
+    {
+      if (fstat (fd, &sbuf) < 0)
+	{
+	  return (NULL);
+	}
+      else if (sbuf.st_size > 0)
+	{
+	  return ((PTR) reuse (fd));
+	}
+    }
+
+  /* We start off with the malloc descriptor allocated on the stack, until
+     we build it up enough to call _mmalloc_mmap_morecore() to allocate the
+     first page of the region and copy it there.  Ensure that it is zero'd and
+     then initialize the fields that we know values for. */
+
+  mdp = &mtemp;
+  memset ((char *) mdp, 0, sizeof (mtemp));
+  strncpy (mdp -> magic, MMALLOC_MAGIC, MMALLOC_MAGIC_SIZE);
+  mdp -> headersize = sizeof (mtemp);
+  mdp -> version = MMALLOC_VERSION;
+  mdp -> morecore = __mmalloc_mmap_morecore;
+  mdp -> fd = fd;
+  mdp -> base = mdp -> breakval = mdp -> top = baseaddr;
+
+  /* If we have not been passed a valid open file descriptor for the file
+     to map to, then open /dev/zero and use that to map to. */
+
+  if (mdp -> fd < 0)
+    {
+      if ((mdp -> fd = open ("/dev/zero", O_RDWR)) < 0)
+	{
+	  return (NULL);
+	}
+      else
+	{
+	  mdp -> flags |= MMALLOC_DEVZERO;
+	}
+    }
+
+  /*  Now try to map in the first page, copy the malloc descriptor structure
+      there, and arrange to return a pointer to this new copy.  If the mapping
+      fails, then close the file descriptor if it was opened by us, and arrange
+      to return a NULL. */
+
+  if ((mbase = mdp -> morecore (mdp, sizeof (mtemp))) != NULL)
+    {
+      memcpy (mbase, mdp, sizeof (mtemp));
+      mdp = (struct mdesc *) mbase;
+    }
+  else
+    {
+      if (mdp -> flags & MMALLOC_DEVZERO)
+	{
+	  close (mdp -> fd);
+	}
+      mdp = NULL;
+    }
+
+  return ((PTR) mdp);
+}
+
+/* Given an valid file descriptor on an open file, test to see if that file
+   is a valid mmalloc produced file, and if so, attempt to remap it into the
+   current process at the same address to which it was previously mapped.
+
+   Note that we have to update the file descriptor number in the malloc-
+   descriptor read from the file to match the current valid one, before
+   trying to map the file in, and again after a successful mapping and
+   after we've switched over to using the mapped in malloc descriptor 
+   rather than the temporary one on the stack.
+
+   Also note that if the heap being remapped previously used the mmcheck()
+   routines, we need to update the hooks since their target functions
+   will have certainly moved if the executable has changed in any way.
+   We do this by calling mmcheck() internally.
+
+   Returns a pointer to the malloc descriptor if successful, or NULL if
+   unsuccessful for some reason. */
+
+static struct mdesc *
+reuse (fd)
+  int fd;
+{
+  struct mdesc mtemp;
+  struct mdesc *mdp = NULL;
+
+  if ((lseek (fd, 0L, SEEK_SET) == 0) &&
+      (read (fd, (char *) &mtemp, sizeof (mtemp)) == sizeof (mtemp)) &&
+      (mtemp.headersize == sizeof (mtemp)) &&
+      (strcmp (mtemp.magic, MMALLOC_MAGIC) == 0) &&
+      (mtemp.version <= MMALLOC_VERSION))
+    {
+      mtemp.fd = fd;
+      if (__mmalloc_remap_core (&mtemp) == mtemp.base)
+	{
+	  mdp = (struct mdesc *) mtemp.base;
+	  mdp -> fd = fd;
+	  if (mdp -> mfree_hook != NULL)
+	    {
+	      (void) mmcheck ((PTR) mdp, (void (*) PARAMS ((void))) NULL);
+	    }
+	}
+    }
+  return (mdp);
+}
+
+#else	/* !defined (HAVE_MMAP) */
+
+/* For systems without mmap, the library still supplies an entry point
+   to link to, but trying to initialize access to an mmap'd managed region
+   always fails. */
+
+PTR
+mmalloc_attach (fd, baseaddr)
+  int fd;
+  PTR baseaddr;
+{
+   return (NULL);
+}
+
+#endif	/* defined (HAVE_MMAP) */
+