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Decoder

This section provides an API reference for the RISC-V instruction decoder functions within R-Visor. These functions are responsible for parsing a raw 32-bit or 16-bit instruction encoding and extracting its constituent fields into an RvInst structure. These functions are generated directly from the ArchVisor sources at compile time.

Decoding Functions

All decode_<Format>type functions, as well as decode_instruction32 and decode_instruction16 , take a single 32-bit unsigned integer representing the instruction bits and return an RvInst structure. The RvInst structure (presumably defined in instructions.h ) contains the decoded fields like opcode, funct3, funct7, registers (rd, rs1, rs2), and immediate values.

The primary dispatching function decode_instruction additionally takes a debug flag.

Standard RISC-V Format Decoders

These functions decode instructions belonging to the standard RISC-V instruction formats (RV32I, RV64I, and common extensions).

RvInst decode_Rtype(uint32_t instruction)

Decodes a 32-bit R-type instruction.

  • Parameters :
    • instruction : The 32-bit raw instruction encoding.
  • Returns: An RvInst structure populated with the decoded fields (opcode, rd, funct3, rs1, rs2, funct7).

RvInst decode_R4type(uint32_t instruction)

Decodes a 32-bit R4-type instruction (typically used for FMADD, FMSUB, etc., involving three source registers rs1, rs2, rs3).

  • Parameters :
    • instruction : The 32-bit raw instruction encoding.
  • Returns: An RvInst structure populated with decoded fields.

RvInst decode_RAMOtype(uint32_t instruction)

Decodes a 32-bit R-type instruction specifically for Atomic Memory Operations (AMO). While structurally similar to R-type, this distinguishes them for clarity or specific field interpretation (like aq and rl bits).

  • Parameters :
    • instruction : The 32-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_Itype(uint32_t instruction)

Decodes a 32-bit I-type instruction (e.g., ADDI, LW, JALR).

  • Parameters :
    • instruction : The 32-bit raw instruction encoding.
  • Returns: An RvInst structure (opcode, rd, funct3, rs1, imm).

RvInst decode_Stype(uint32_t instruction)

Decodes a 32-bit S-type instruction (e.g., SW, SB).

  • Parameters :
    • instruction : The 32-bit raw instruction encoding.
  • Returns: An RvInst structure (opcode, imm[4:0], funct3, rs1, rs2, imm[11:5]).

RvInst decode_Utype(uint32_t instruction)

Decodes a 32-bit U-type instruction (e.g., LUI, AUIPC).

  • Parameters :
    • instruction : The 32-bit raw instruction encoding.
  • Returns: An RvInst structure (opcode, rd, imm[31:12]).

RvInst decode_Btype(uint32_t instruction)

Decodes a 32-bit B-type instruction (e.g., BEQ, BNE).

  • Parameters :
    • instruction : The 32-bit raw instruction encoding.
  • Returns: An RvInst structure (opcode, imm[11], imm[4:1], funct3, rs1, rs2, imm[10:5], imm[12]).

RvInst decode_Jtype(uint32_t instruction)

Decodes a 32-bit J-type instruction (e.g., JAL).

  • Parameters :
    • instruction : The 32-bit raw instruction encoding.
  • Returns: An RvInst structure (opcode, rd, imm[19:12], imm[11], imm[10:1], imm[20]).

Compressed Instruction Format Decoders (RISC-V 'C' Extension)

These functions decode 16-bit compressed instructions. Note that they still take a uint32_t as input, but will typically only process the lower 16 bits.

RvInst decode_CRtype(uint32_t instruction)

Decodes a 16-bit CR-format compressed instruction (e.g., C.MV, C.ADD).

  • Parameters :
    • instruction : The 16-bit raw instruction encoding (passed as uint32_t).
  • Returns: An RvInst structure.

RvInst decode_CRItype(uint32_t instruction)

This seems to be a typo and might intend to be decode_CItype for instructions like C.ADDI or specific immediate versions of CR format. Assuming it's distinct from decode_CItype , it decodes a specific 16-bit compressed format involving an immediate.

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CItype(uint32_t instruction)

Decodes a 16-bit CI-format compressed instruction (e.g., C.LI, C.LUI, C.ADDI).

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CIStype(uint32_t instruction)

Decodes a 16-bit CI-format compressed instruction specifically for stack-pointer based loads/stores if rd/ rs1 is SP (e.g. C.LWSP, C.SWSP). The naming suggests it might be a more specific CI variant or a typo for CSS-type. Given decode_CSStype exists, this is likely a specific CI sub-format.

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CISDtype(uint32_t instruction)

Likely decodes a 16-bit CI-format compressed instruction for stack-pointer based double-word loads (e.g., C.LDSP) from RV64C/RV128C.

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CI16type(uint32_t instruction)

Decodes a 16-bit CI-format compressed instruction like C.ADDI16SP.

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CSStype(uint32_t instruction)

Decodes a 16-bit CSS-format compressed instruction (e.g., C.SWSP).

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CSSDtype(uint32_t instruction)

Decodes a 16-bit CSS-format compressed instruction for stack-pointer based double-word stores (e.g., C.SDSP) from RV64C/RV128C.

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CIWtype(uint32_t instruction)

Decodes a 16-bit CIW-format compressed instruction (e.g., C.ADDIW).

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CLtype(uint32_t instruction)

Decodes a 16-bit CL-format compressed instruction (e.g., C.LW, C.FLW).

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CLDtype(uint32_t instruction)

Decodes a 16-bit CL-format compressed instruction for double-word loads (e.g., C.LD, C.FLD) from RV64C/RV128C.

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CStype(uint32_t instruction)

Decodes a 16-bit CS-format compressed instruction (e.g., C.SW, C.FSW).

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CSDtype(uint32_t instruction)

Decodes a 16-bit CS-format compressed instruction for double-word stores (e.g., C.SD, C.FSD) from RV64C/RV128C.

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CBtype(uint32_t instruction)

Decodes a 16-bit CB-format compressed instruction (e.g., C.BEQZ, C.BNEZ, C.ADDIW).

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CBItype(uint32_t instruction)

This seems to be a typo or a specific sub-format of CB. It likely decodes a 16-bit compressed branch format that also incorporates an immediate field not covered by the general CB, or specific CB instructions like C.SLLI.

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_CJtype(uint32_t instruction)

Decodes a 16-bit CJ-format compressed instruction (e.g., C.J, C.JAL).

  • Parameters :
    • instruction : The 16-bit raw instruction encoding.
  • Returns: An RvInst structure.

General Instruction Decoders

These functions handle the initial dispatch or decode based on instruction size.

RvInst decode_instruction32(uint32_t instruction)

Decodes a 32-bit instruction by determining its specific format (R, I, S, U, B, J) and calling the appropriate format-specific decoder.

  • Parameters :
    • instruction : The 32-bit raw instruction encoding.
  • Returns: An RvInst structure.

RvInst decode_instruction16(uint32_t instruction)

Decodes a 16-bit compressed instruction by determining its specific format (CR, CI, CS, etc.) and calling the appropriate compressed format-specific decoder. Processes the lower 16 bits of the input.

  • Parameters :
    • instruction : The 16-bit raw instruction encoding (passed as uint32_t).
  • Returns: An RvInst structure.

RvInst decode_instruction(uint32_t instruction, int debug)

The main dispatch function for decoding an instruction. It first determines if the instruction is 16-bit (compressed) or 32-bit based on its lowest two bits and then calls either decode_instruction16 or decode_instruction32 .

  • Parameters :
    • instruction : The raw instruction encoding (can be 16-bit or 32-bit, passed as uint32_t).
    • debug : An integer flag; if non-zero, it may enable debug printing (using printUtils.h ) during the decoding process.
  • Returns: An RvInst structure containing the decoded fields.