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Added note to cbuildcap and reserved cs1 == 0 #103

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Feb 12, 2024
Merged

Added note to cbuildcap and reserved cs1 == 0 #103

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f9dafad
Added note to cbuildcap and reserved cs1 == 0
francislaus Feb 9, 2024
4c329ca
changed note as discussed in the PR
francislaus Feb 11, 2024
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8 changes: 6 additions & 2 deletions src/insns/cbuildcap_32bit.adoc
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Expand Up @@ -24,8 +24,12 @@ sealed, `cs1` 's permissions and bounds are equal or a superset of `cs2` 's,
`cs2` 's bounds are not malformed (see
xref:section_cap_malformed[xrefstyle=short]), and all reserved bits in `cs2` 's
metadata are 0. <<CBUILDCAP>> is typically used alongside <<CSETHIGH>> to build
capabilities from integer values. The case `cs1 == 0` trivially leads to the tag
of `cd` being stripped.
capabilities from integer values.

NOTE: The case `cs1 == 0` trivially leads to the tag of `cd` being stripped.
We opted to not make this a pseudo instruction to clear the tag of capability.
`cbuildcap cd, c0, cs2` will behave differently in the case of otypes being
added. Thus we reserve the encoding `cs1 == 0` for now.
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Prerequisites::
{cheri_base_ext_name}
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2 changes: 1 addition & 1 deletion src/insns/wavedrom/cbuildcap.adoc
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Expand Up @@ -5,7 +5,7 @@
{bits: 7, name: 'opcode', attr: ['7', 'OP=0110011'], type: 8},
{bits: 5, name: 'cd', attr: ['5', 'dest'], type: 2},
{bits: 3, name: 'funct3', attr: ['3', 'CBUILDCAP=101'], type: 8},
{bits: 5, name: 'cs1', attr: ['5', 'src1'], type: 4},
{bits: 5, name: 'cs1', attr: ['5', 'src1 != 0'], type: 4},
{bits: 5, name: 'cs2', attr: ['5', 'src2'], type: 3},
{bits: 7, name: 'funct7', attr: ['7', 'CBUILDCAP=0000110'], type: 3},
]}
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