# notes.txt -rw-r--r-- 2.0 KiB View raw
                                                                                
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- 32-bit capability addresses (64 in practice on x86_64)
- if addressing the last slot, that refers to the cspace itself
  - when referencing this slot, the cspace is referenced
  - when allocating to this slot, an address is assigned

k = cspace bits (1 << k slots)
g = cspace guard bits

  cspace A
  k=8  g=0
+==========+
|   ....   |
|          |            cspace B
+----------+            k=8  g=4
| cnode    | 0x42 --> +==========+
+----------+          |   ....   |
|   ....   |          |          |            cspace C
|          |          +----------+            k=16 g=4
+----------+          | cnode    | 0x24 --> +==========+
|%reserved%| 0xFF     +----------+          |   ....   |
+==========+          |   ....   |          |          |
                      |          |          +----------+
                      +----------+          | page     | 0xBEEF
                      |%reserved%| 0xFF     +----------+
                      +==========+          |   ....   |
                                            |          |
                                            +----------+
                                            |%reserved%| 0xFFFF
                                            +==========+


Example capability address:

0xAAGBBGCC
  | || ||
  +-||-||----> cspace A slot address
    +|-||----> cspace B guard (always zero)
     +-||----> cspace B slot address
       +|----> cspace C guard (always zero)
        +----> cspace C slot address

Page capability in cspace C:    0x420240BEEF
cspace B:                       0x420FFFFFFF (last 24 bits not used)
cspace C:                       0x42024FFFFF

To allocate a new page in cspace B, address slot 0x420FFFFFFF

Example usage scenario: process manager spawns a process
- The process manager's cspace is k=8 g=24
- A cspace of process caps is kept at 0x80XXXYYY (k=12)
- The cspace for pid 0x123 is thus at 0x80123YYY
- To insert caps into the new process, process manager addresses them at
  0x80123YYY (or 0x80123FFF to capalloc)
- To destroy the process, the process manager just destroys 0x80123FFF