Add support for sfence.vma instruction

[buildandcrash]

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• I've added tests (optional)
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Description

This pull request adds support for the sfence.vma instruction to the RISC-V plugin in Radare2 and fixes (#23021).

Changes Made:

Introduced sfence.vma instruction mnemonic, operand definition, and opcode matching in riscv.c.
Updated the opcode table (riscv_builtin_opcodes) to include sfence.vma with its corresponding opcode values and operand specifications.
Reason for Change:
The sfence.vma instruction is part of the RISC-V ISA and is used for flushing virtual memory address translations. Including support for sfence.vma enhances the completeness of the RISC-V plugin in Radare2, enabling better analysis and disassembly capabilities for binaries that utilize this instruction.

Testing:

Manually tested the functionality by disassembling binaries containing sfence.vma instructions.
Verified proper decoding and disassembly output alignment with RISC-V specifications.

Before:

rasm2 -D -a riscv -b 64 73000012
0x00000000   4                 73000012  invalid

After:

rasm2 -D -a riscv -b 64 73000012
0x00000000   4                 73000012  sfence.vma zero, zero

Additional Notes:

This change ensures compatibility with the latest RISC-V ISA extensions and improves the utility of Radare2 for analyzing modern RISC-V binaries.

[trufae]

Sweet! thanks for your contribution! would you like to continue extending the stock disassembler to support more VMA instructions? I bet there will be other pretty common ones around the same code.

Also, how is this instruction recognized by the analizer? because it should be reported as a different family (privileged or thready maybe)

[buildandcrash]

Thank you! Contributing to radare2 would be an honor. I will add support to anything missing as I go, since I am working on RISC-V projects these days.

Also, the sfence.vma instruction was a replacement for sfence.vm which is considered an "improved" privileged instruction

[trufae]

Awesome! glad to have some riscv improvements, i love this arch but i can't spent fulltime on it yet. Btw if you care about decompilation maybe you can also check this PR wargio/r2dec-js#291