[src/trunk]: src/sys/compat/osf1 evil hack to work around non-fixed mmap requ...

[cgd <cgd%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/6fadd2e0c8fd
branches:  trunk
changeset: 472313:6fadd2e0c8fd
user:      cgd <cgd%NetBSD.org@localhost>
date:      Tue Apr 27 06:37:12 1999 +0000

description:
evil hack to work around non-fixed mmap requests

diffstat:

 sys/compat/osf1/osf1_misc.c |  72 +++++++++++++++++++++++++++++++++++++++++---
 1 files changed, 67 insertions(+), 5 deletions(-)

diffs (93 lines):

diff -r 31d91afe77d5 -r 6fadd2e0c8fd sys/compat/osf1/osf1_misc.c
--- a/sys/compat/osf1/osf1_misc.c       Tue Apr 27 06:08:58 1999 +0000
+++ b/sys/compat/osf1/osf1_misc.c       Tue Apr 27 06:37:12 1999 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: osf1_misc.c,v 1.24 1999/04/26 18:34:05 cgd Exp $ */
+/* $NetBSD: osf1_misc.c,v 1.25 1999/04/27 06:37:12 cgd Exp $ */
 
 /*
  * Copyright (c) 1999 Christopher G. Demetriou.  All rights reserved.
@@ -75,6 +75,8 @@
 #include <sys/exec.h>
 #include <sys/vnode.h>
 #include <sys/socketvar.h>
+#include <vm/vm.h>                             /* XXX UVM headers are Cool */
+#include <uvm/uvm.h>                           /* XXX see mmap emulation */
 
 #include <compat/osf1/osf1.h>
 #include <compat/osf1/osf1_syscall.h>
@@ -305,10 +307,70 @@
        if (leftovers != 0)
                return (EINVAL);
 
-#if 0
-       /* XXX EVIL!!! */
-       SCARG(&a, flags) |= MAP_FIXED;
-#endif
+       /*
+        * XXX The following code is evil.
+        *
+        * The OSF/1 mmap() function attempts to map non-fixed entries
+        * near the address that the user specified.  Therefore, for
+        * non-fixed entires we try to find space in the address space
+        * starting at that address.  If the user specified zero, we
+        * start looking at at least NBPG, so that programs can't
+        * accidentally live through deferencing NULL.
+        *
+        * The need for this kludgery is increased by the fact that
+        * the loader data segment is mapped at
+        * (end of user address space) - 1G, MAXDSIZ is 1G, and
+        * the VM system tries allocate non-fixed mappings _AFTER_
+        * (start of data) + MAXDSIZ.  With the loader, of course,
+        * that means that it'll start trying at
+        * (end of user address space), and will never succeed!
+        *
+        * Notes:
+        *
+        * * Though we find space here, if something else (e.g. a second
+        *   thread) were mucking with the address space the mapping
+        *   we found might be used by another mmap(), and this call
+        *   would clobber that region.
+        *
+        * * In general, tricks like this only work for MAP_ANON mappings,
+        *   because of sharing/cache issues.  That's not a problem on
+        *   the Alpha, and though it's not good style to abuse that fact,
+        *   there's little choice.
+        *
+        * * In order for this to be done right, the VM system should
+        *   really try to use the requested 'addr' passed in to mmap()
+        *   as a hint, even if non-fixed.  If it's passed as zero,
+        *   _maybe_ then try (start of data) + MAXDSIZ, or maybe
+        *   provide a better way to avoid the data region altogether.
+        */
+       if ((SCARG(&a, flags) & MAP_FIXED) == 0) {
+               vaddr_t addr = round_page(SCARG(&a, addr));
+               vsize_t size = round_page(SCARG(&a, len));
+               int fixed = 0;
+
+               vm_map_lock(&p->p_vmspace->vm_map);
+
+               /* if non-NULL address given, start looking there */
+               if (addr != 0 && uvm_map_findspace(&p->p_vmspace->vm_map,
+                   addr, size, &addr, NULL, 0, 0) != NULL) {
+                       fixed = 1;
+                       goto done;
+               }
+
+               /* didn't find anything.  take it again from the top. */
+               if (uvm_map_findspace(&p->p_vmspace->vm_map, NBPG, size, &addr,
+                   NULL, 0, 0) != NULL) {
+                       fixed = 1;
+                       goto done;
+               }
+
+done:
+               vm_map_unlock(&p->p_vmspace->vm_map);
+               if (fixed) {
+                       SCARG(&a, flags) |= MAP_FIXED;
+                       SCARG(&a, addr) = (void *)addr;
+               }
+       }
 
        return sys_mmap(p, &a, retval);
 }