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Section with Special Capabilities #62

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Section with Special Capabilities #62

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29 changes: 18 additions & 11 deletions src/cap-description.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -426,23 +426,21 @@ if ( (E < (CAP_MAX_E - 1)) & (t[XLENMAX: XLENMAX - 1] - b[XLENMAX - 1] > 1) )
That is, invert the most significant bit of _t_ if the decoded length of the
capability is larger than E.

[#section_null_inf_cap]
=== NULL and Infinite Capabilities
[#section_special_caps]
=== Special Capabilities

[#section_null_cap]
==== NULL Capability

ifdef::cheri_v9_annotations[]
NOTE: *CHERI v9 Note:* Encoding <<null-cap>> as zeros removes the need for
the difference between in-memory and architectural format.
endif::[]

The <<null-cap>> capability is represented with 0 in all fields. This implies
that <<null-cap>> has no permissions and its exponent E is CAP_MAX_E e.g. 52
when XLENMAX=64, so its bounds cover the entire address space such that the
expanded base is 0 and top is 2^XLENMAX^. In contrast, the <<infinite-cap>>
capability grants all permissions while its bounds also cover the whole address
space.

NOTE: The <<infinite-cap>> capability is also known as 'default', 'almighty',
or 'root' capability.
The <<null-cap>> capability is represented with 0 in all fields. This implies
that it has no permissions and its exponent E is CAP_MAX_E (52 for XLENMAX=64,
24 for XLENMAX=32), so its bounds cover the entire address space such that the
expanded base is 0 and top is 2^XLENMAX^.

.Field values of the NULL capability
[#null-cap,reftext="NULL",options=header,align=center,width="55%",cols="1,1,3"]
Expand All @@ -461,6 +459,15 @@ or 'root' capability.
| Reserved| zeros | All reserved fields
|==============================================================================

[#section_infinite_cap]
==== Infinite Capability

The <<infinite-cap>> capability grants all permissions while its bounds also
cover the whole address space.

NOTE: The <<infinite-cap>> capability is also known as 'default', 'almighty',
or 'root' capability.

.Field values of the Infinite capability
[#infinite-cap,reftext="Infinite"]
[options=header,width="100%",align=center,width="55%",cols="1,1,3"]
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