[PATCH 1/5] htl: Let Mach place thread stacks

[Sergey Bugaev]

Instead of trying to allocate a thread stack at a specific address,
looping over the address space, just set the ANYWHERE flag in
vm_allocate (). The previous behavior:

- defeats ASLR (for Mach versions that support ASLR),
- is particularly slow if the lower 4 GB of the address space are mapped
  inaccessible, as we're planning to do on 64-bit Hurd,
- is just silly.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
---
 sysdeps/mach/htl/pt-stack-alloc.c | 35 ++++++-------------------------
 1 file changed, 6 insertions(+), 29 deletions(-)

diff --git a/sysdeps/mach/htl/pt-stack-alloc.c 
b/sysdeps/mach/htl/pt-stack-alloc.c
index 429ac2d9..97e6b445 100644
--- a/sysdeps/mach/htl/pt-stack-alloc.c
+++ b/sysdeps/mach/htl/pt-stack-alloc.c
@@ -19,14 +19,9 @@
 #include <errno.h>
 
 #include <mach.h>
-#include <mach/machine/vm_param.h>
 
 #include <pt-internal.h>
 
-/* The next address to use for stack allocation.  */
-static vm_address_t next_stack_base = VM_MIN_ADDRESS;
-
-
 /* Allocate a new stack of size STACKSIZE.  If successful, store the
    address of the newly allocated stack in *STACKADDR and return 0.
    Otherwise return an error code (EINVAL for an invalid stack size,
@@ -35,30 +30,12 @@ static vm_address_t next_stack_base = VM_MIN_ADDRESS;
 int
 __pthread_stack_alloc (void **stackaddr, size_t stacksize)
 {
-  vm_offset_t base;
-  int i = 0;
-
-get_stack:
-  i++;
-  for (base = next_stack_base;
-       base < VM_MAX_ADDRESS
-       && __vm_allocate (__mach_task_self (), &base,
-                        stacksize, FALSE) != KERN_SUCCESS; base += stacksize)
-    ;
-
-  if (base >= VM_MAX_ADDRESS)
-    {
-      if (i == 1)
-       {
-         next_stack_base = VM_MIN_ADDRESS;
-         goto get_stack;
-       }
-      else
-       return EAGAIN;
-    }
+  error_t err;
 
-  next_stack_base = base + stacksize;
+  err = __vm_allocate (__mach_task_self (), (vm_offset_t *) stackaddr,
+                      stacksize, TRUE);
 
-  (*stackaddr) = (void *) base;
-  return 0;
+  if (err == KERN_NO_SPACE)
+    err = EAGAIN;
+  return err;
 }
-- 
2.41.0