[PATCH v2 0/3] gnumach VM entry re-coalescing

[Sergey Bugaev]

This is the remaining patches from "Forward merging entries and other
VM shenanigans" (specifically the vm_map_coalesce_entry part), with
that one issue fixed. And here's a reproducer that fails with v1 and
works now:

Sergey


#define _GNU_SOURCE

#include <stdio.h>
#include <mach.h>
#include <error.h>
#include <errno.h>
#include <unistd.h>
#include <spawn.h>
#include <sys/wait.h>

int
main ()
{
  error_t err;
  vm_offset_t offset;
  extern char **environ;
  pid_t pid;
  int *ptr;
  char *child_argv[] = { "vminfo", NULL, NULL };

  asprintf (&child_argv[1], "%d", getpid ());

  /* Allocate space for four pages.  */
  err = vm_allocate (mach_task_self (), &offset, vm_page_size * 4, 1);
  if (err)
    error (1, err, "vm_allocate space");

  printf ("Allocated at %p\n", (void *) (offset + vm_page_size));

  /* Deallocate them back!  */
  err = vm_deallocate (mach_task_self (), offset, vm_page_size * 4);
  if (err)
    error (1, err, "vm_deallocate space");

  offset += vm_page_size;

  /* Allocate the two pages.  */
  err = vm_allocate (mach_task_self (), &offset, vm_page_size * 2, 0);
  if (err)
    error (1, err, "vm_allocate");

  ptr = (int *) (offset + vm_page_size);

  /* Realize the object.  */
  *ptr = 1234;

  /* Deallocate the first page, and reallocate it
     with a different protection.  */
  err = vm_deallocate (mach_task_self (), offset, vm_page_size);
  if (err)
    error (1, err, "vm_deallocate page");

  err = vm_map (mach_task_self (), &offset, vm_page_size, 0, 0,
                MACH_PORT_NULL, 0, 0, VM_PROT_ALL, VM_PROT_ALL,
                VM_INHERIT_COPY);
  if (err)
    error (1, err, "vm_map");

  printf ("====== Before coalescing ======\n");
  fflush (stdout);
  posix_spawn (&pid, "/bin/vminfo", NULL, NULL, child_argv, environ);
  wait (NULL);

  /* Coalesce the two entries back together.  */
  err = vm_protect (mach_task_self (), offset,
                    vm_page_size, 0, VM_PROT_DEFAULT);
  if (err)
    error (1, err, "vm_protect (VM_PROT_DEFAULT)");

  printf ("====== After coalescing ======\n");
  fflush (stdout);
  posix_spawn (&pid, "/bin/vminfo", NULL, NULL, child_argv, environ);
  wait (NULL);

  /* Check whether the data is still there.  */
  printf ("%d\n", *(const int *) (offset + vm_page_size));
}