Make core-dumps have all the relevant regions in it.

Based on input from Roland McGrath and Hugh Dickins.

This simplifies the logic, and takes advantage of the
"new" VM information in the form of vma->anon_vma.

fs/binfmt_elf.c

@@ -1054,22 +1054,14 @@ static int dump_seek(struct file *file, off_t off)
  */
 static int maydump(struct vm_area_struct *vma)
 {
-	/*
-	 * If we may not read the contents, don't allow us to dump
-	 * them either. "dump_write()" can't handle it anyway.
-	 */
-	if (!(vma->vm_flags & VM_READ))
+	/* Do not dump I/O mapped devices, shared memory, or special mappings */
+	if (vma->vm_flags & (VM_IO | VM_SHARED | VM_RESERVED))
 		return 0;
 
-	/* Do not dump I/O mapped devices! -DaveM */
-	if (vma->vm_flags & VM_IO)
-		return 0;
-#if 1
-	if (vma->vm_flags & (VM_WRITE|VM_GROWSUP|VM_GROWSDOWN))
-		return 1;
-	if (vma->vm_flags & (VM_READ|VM_EXEC|VM_EXECUTABLE|VM_SHARED))
+	/* If it hasn't been written to, don't write it out */
+	if (!vma->anon_vma)
 		return 0;
-#endif
+
 	return 1;
 }