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Add Tag_RISCV_mop_and_hint_encoding for instruction reinterpretation #474

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Add Tag_RISCV_mop_and_hint_encoding for instruction reinterpretation #474

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Add Tag_RISCV_mop_and_hint_encoding for instruction reinterpretation
kito-cheng Aug 11, 2025
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kito-cheng Sep 5, 2025
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29 changes: 29 additions & 0 deletions riscv-elf.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -1272,6 +1272,7 @@ non-standard ABI extensions.
| Tag_RISCV_priv_spec_revision | 12 | uleb128 | *Deprecated*, indicates the revision version of the privileged specification.
| Tag_RISCV_atomic_abi | 14 | uleb128 | Indicates which version of the atomics ABI is being used.
| Tag_RISCV_x3_reg_usage | 16 | uleb128 | Indicates the usage definition of the X3 register.
| Tag_RISCV_mop_and_hint_encoding | 18 | uleb128 | Indicates the reinterpretation of MOP and hint instruction encodings.
| Reserved for non-standard attribute | >= 32768 | - | -
|===

Expand Down Expand Up @@ -1437,6 +1438,34 @@ value. After the merge, the resulting value will be the non-zero one.

--

===== Tag_RISCV_mop_and_hint_encoding, 18, uleb128=value

Tag_RISCV_mop_and_hint_encoding indicates the reinterpretation of MOP (Maybe Operation)
and hint instruction encodings within this object. The value is a bitmap where each bit
indicates whether specific instruction encodings should be reinterpreted:

[horizontal]
Bit 0 (Zicfilp):: When set, `auipc x0, <value>` instructions are interpreted as `lpad <value>`.
Bit 1 (Zicfiss):: When set, Zimop encoding space instructions are interpreted as Zicfiss instructions.
Bit 2 (Zihintpause):: When set, `fence w,0` instructions are interpreted as `pause` hints.
Bit 3 (Zihintntl):: When set, specific instruction encodings are interpreted as non-temporal locality hints.

--

Merge policy:::
Values are merged using bitwise OR operation.

NOTE: The bitwise OR merge policy may cause disassembler confusion when the same encoding
space is redefined by multiple bits. Toolchains may report warnings to alert users
when such conflicts occur.

--

NOTE: When specific bits are set, toolchains must disassemble instructions according to
the corresponding extensions regardless of whether these extensions are enabled. For example,
if bit 0 is set, `auipc x0, <value>` must be disassembled as `lpad <value>`; if bit 1 is
set, Zimop encodings must be disassembled as Zicfiss instructions.

=== Program Property

Program properties are used to record information about an object file or binary
Expand Down