Thanks for looking into it.  I committed the following into the Emacs
trunk as bzr 105287.  It addresses all the issues I saw, except for
the MIPS port.  The files for that don't look right: they
define a bunch of symbols that Emacs no longer uses.  The only symbol
that is current is VIRT_ADDR_VARIES, so maybe we'll have to fold
that in somehow, but that probably belongs in s/openbsd.h anyway.
Anyway, perhaps if you could get the person who does the MIPS port into
the discussion, so that they can explain what goes wrong on MIPS without
that patch, we could fix the MIPS port too.

======

Port to OpenBSD.
See http://lists.gnu.org/archive/html/emacs-devel/2011-07/msg00688.html
and the surrounding thread.
* minibuf.c (read_minibuf_noninteractive): Rewrite to use getchar
rather than fgets, and retry after EINTR.  Otherwise, 'emacs
--batch -f byte-compile-file' fails on OpenBSD if an inactivity
timer goes off.
* s/openbsd.h (BROKEN_SIGIO): Define.
* unexelf.c (unexec) [__OpenBSD__]:
Don't update the .mdebug section of the Alpha COFF symbol table.
=== modified file 'src/minibuf.c'
--- src/minibuf.c       2011-06-24 21:25:22 +0000
+++ src/minibuf.c       2011-07-19 15:46:18 +0000
@@ -19,6 +19,7 @@

 #include <config.h>
+#include <errno.h>
 #include <stdio.h>
 #include <setjmp.h>

@@ -236,8 +237,9 @@
                             int allow_props, int inherit_input_method)
 {
   ptrdiff_t size, len;
-  char *line, *s;
+  char *line;
   Lisp_Object val;
+  int c;

   fprintf (stdout, "%s", SDATA (prompt));
   fflush (stdout);
@@ -246,22 +248,30 @@
   size = 100;
   len = 0;
   line = (char *) xmalloc (size);
-  while ((s = fgets (line + len, size - len, stdin)) != NULL
-        && (len = strlen (line),
-            len == size - 1 && line[len - 1] != '\n'))
+
+  while ((c = getchar ()) != '\n')
     {
-      if (STRING_BYTES_BOUND / 2 < size)
-       memory_full (SIZE_MAX);
-      size *= 2;
-      line = (char *) xrealloc (line, size);
+      if (c < 0)
+       {
+         if (errno != EINTR)
+           break;
+       }
+      else
+       {
+         if (len == size)
+           {
+             if (STRING_BYTES_BOUND / 2 < size)
+               memory_full (SIZE_MAX);
+             size *= 2;
+             line = (char *) xrealloc (line, size);
+           }
+         line[len++] = c;
+       }
     }

-  if (s)
+  if (len)
     {
-      char *nl = strchr (line, '\n');
-      if (nl)
-       *nl = '\0';
-      val = build_string (line);
+      val = make_string (line, len);
       xfree (line);
     }
   else

=== modified file 'src/s/openbsd.h'
--- src/s/openbsd.h     2011-01-15 23:16:57 +0000
+++ src/s/openbsd.h     2011-07-19 17:19:32 +0000
@@ -1,5 +1,9 @@
 /* System file for openbsd.  */

-/* The same as NetBSD.  Note there are differences in configure.  */
+/* Nearly the same as NetBSD.  Note there are differences in configure.  */
 #include "netbsd.h"

+/* The symbol SIGIO is defined, but the feature doesn't work in the
+   way Emacs needs it to.  See
+   <http://article.gmane.org/gmane.os.openbsd.ports/46831>.  */
+#define BROKEN_SIGIO

=== modified file 'src/unexelf.c'
--- src/unexelf.c       2011-06-13 05:55:57 +0000
+++ src/unexelf.c       2011-07-19 16:47:05 +0000
@@ -1053,7 +1053,7 @@
       memcpy (NEW_SECTION_H (nn).sh_offset + new_base, src,
              NEW_SECTION_H (nn).sh_size);

-#ifdef __alpha__
+#if defined __alpha__ && !defined __OpenBSD__
       /* Update Alpha COFF symbol table: */
       if (strcmp (old_section_names + OLD_SECTION_H (n).sh_name, ".mdebug")
          == 0)
@@ -1072,7 +1072,7 @@
          symhdr->cbRfdOffset += new_data2_size;
          symhdr->cbExtOffset += new_data2_size;
        }
-#endif /* __alpha__ */
+#endif /* __alpha__ && !__OpenBSD__ */

 #if defined (_SYSTYPE_SYSV)
       if (NEW_SECTION_H (nn).sh_type == SHT_MIPS_DEBUG