// SPDX-License-Identifier: (Apache-2.0 OR MIT)
// Copyright 2017 6WIND S.A. <quentin.monnet@6wind.com>

//! Functions in this module are used to handle eBPF programs with a higher level representation,
//! for example to disassemble the code into a human-readable format.

use alloc::{
    format,
    string::{String, ToString},
    vec,
    vec::Vec,
};

use log::warn;

use crate::ebpf;

#[inline]
fn alu_imm_str(name: &str, insn: &ebpf::Insn) -> String {
    format!("{name} r{}, {:#x}", insn.dst, insn.imm)
}

#[inline]
fn alu_reg_str(name: &str, insn: &ebpf::Insn) -> String {
    format!("{name} r{}, r{}", insn.dst, insn.src)
}

#[inline]
fn byteswap_str(name: &str, insn: &ebpf::Insn) -> String {
    match insn.imm {
        16 | 32 | 64 => {}
        _ => warn!("[Disassembler] Warning: Invalid offset value for {name} insn"),
    }
    format!("{name}{} r{}", insn.imm, insn.dst)
}

#[inline]
fn ld_st_imm_str(name: &str, insn: &ebpf::Insn) -> String {
    if insn.off >= 0 {
        format!("{name} [r{}+{:#x}], {:#x}", insn.dst, insn.off, insn.imm)
    } else {
        format!(
            "{name} [r{}-{:#x}], {:#x}",
            insn.dst,
            -(insn.off as isize),
            insn.imm
        )
    }
}

#[inline]
fn ld_reg_str(name: &str, insn: &ebpf::Insn) -> String {
    if insn.off >= 0 {
        format!("{name} r{}, [r{}+{:#x}]", insn.dst, insn.src, insn.off)
    } else {
        format!(
            "{name} r{}, [r{}-{:#x}]",
            insn.dst,
            insn.src,
            -(insn.off as isize)
        )
    }
}

#[inline]
fn st_reg_str(name: &str, insn: &ebpf::Insn) -> String {
    if insn.off >= 0 {
        format!("{name} [r{}+{:#x}], r{}", insn.dst, insn.off, insn.src)
    } else {
        format!(
            "{name} [r{}-{:#x}], r{}",
            insn.dst,
            -(insn.off as isize),
            insn.src
        )
    }
}

#[inline]
fn ldabs_str(name: &str, insn: &ebpf::Insn) -> String {
    format!("{name} {:#x}", insn.imm)
}

#[inline]
fn ldind_str(name: &str, insn: &ebpf::Insn) -> String {
    format!("{name} r{}, {:#x}", insn.src, insn.imm)
}

#[inline]
fn jmp_imm_str(name: &str, insn: &ebpf::Insn) -> String {
    if insn.off >= 0 {
        format!("{name} r{}, {:#x}, +{:#x}", insn.dst, insn.imm, insn.off)
    } else {
        format!(
            "{name} r{}, {:#x}, -{:#x}",
            insn.dst,
            insn.imm,
            -(insn.off as isize)
        )
    }
}

#[inline]
fn jmp_reg_str(name: &str, insn: &ebpf::Insn) -> String {
    if insn.off >= 0 {
        format!("{name} r{}, r{}, +{:#x}", insn.dst, insn.src, insn.off)
    } else {
        format!(
            "{name} r{}, r{}, -{:#x}",
            insn.dst,
            insn.src,
            -(insn.off as isize)
        )
    }
}

/// High-level representation of an eBPF instruction.
///
/// In addition to standard operation code and various operand, this struct has the following
/// properties:
///
/// * It stores a name, corresponding to a mnemonic for the operation code.
/// * It also stores a description, which is a mnemonic for the full instruction, using the actual
///   values of the relevant operands, and that can be used for disassembling the eBPF program for
///   example.
/// * Immediate values are stored in an `i64` instead of a traditional i32, in order to merge the
///   two parts of (otherwise double-length) `LD_DW_IMM` instructions.
///
/// See <https://www.kernel.org/doc/Documentation/networking/filter.txt> for the Linux kernel
/// documentation about eBPF, or <https://github.com/iovisor/bpf-docs/blob/master/eBPF.md> for a
/// more concise version.
#[derive(Debug, PartialEq, Eq)]
pub struct HLInsn {
    /// Operation code.
    pub opc: u8,
    /// Name (mnemonic). This name is not canon.
    pub name: String,
    /// Description of the instruction. This is not canon.
    pub desc: String,
    /// Destination register operand.
    pub dst: u8,
    /// Source register operand.
    pub src: u8,
    /// Offset operand.
    pub off: i16,
    /// Immediate value operand. For `LD_DW_IMM` instructions, contains the whole value merged from
    /// the two 8-bytes parts of the instruction.
    pub imm: i64,
}

/// Return a vector of `struct HLInsn` built from an eBPF program.
///
/// This is made public to provide a way to manipulate a program as a vector of instructions, in a
/// high-level format, for example for dumping the program instruction after instruction with a
/// custom format.
///
/// Note that the two parts of `LD_DW_IMM` instructions (that have the size of two standard
/// instructions) are considered as making a single immediate value. As a consequence, the number
/// of instructions stored in the vector may not be equal to the size in bytes of the program
/// divided by the length of an instructions.
///
/// To do so, the immediate value operand is stored as an `i64` instead as an i32, so be careful
/// when you use it (see example `examples/to_json.rs`).
///
/// This is to oppose to `ebpf::to_insn_vec()` function, that treats instructions on a low-level
/// ground and do not merge the parts of `LD_DW_IMM`. Also, the version in `ebpf` module does not
/// use names or descriptions when storing the instructions.
///
/// # Examples
///
/// ```
/// use rbpf::disassembler;
///
/// let prog = &[
///     0x18, 0x00, 0x00, 0x00, 0x88, 0x77, 0x66, 0x55,
///     0x00, 0x00, 0x00, 0x00, 0x44, 0x33, 0x22, 0x11,
///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
/// ];
///
/// let v = disassembler::to_insn_vec(prog);
/// assert_eq!(v, vec![
///     disassembler::HLInsn {
///         opc: 0x18,
///         name: "lddw".to_string(),
///         desc: "lddw r0, 0x1122334455667788".to_string(),
///         dst: 0,
///         src: 0,
///         off: 0,
///         imm: 0x1122334455667788
///     },
///     disassembler::HLInsn {
///         opc: 0x95,
///         name: "exit".to_string(),
///         desc: "exit".to_string(),
///         dst: 0,
///         src: 0,
///         off: 0,
///         imm: 0
///     },
/// ]);
/// ```
pub fn to_insn_vec(prog: &[u8]) -> Vec<HLInsn> {
    if prog.len() % ebpf::INSN_SIZE != 0 {
        panic!(
            "[Disassembler] Error: eBPF program length must be a multiple of {:?} octets",
            ebpf::INSN_SIZE
        );
    }
    if prog.is_empty() {
        return vec![];
    }

    let mut res = vec![];
    let mut insn_ptr: usize = 0;

    while insn_ptr * ebpf::INSN_SIZE < prog.len() {
        let insn = ebpf::get_insn(prog, insn_ptr);

        let name;
        let desc;
        let mut imm = insn.imm as i64;
        match insn.opc {
            // BPF_LD class
            ebpf::LD_ABS_B => {
                name = "ldabsb";
                desc = ldabs_str(name, &insn);
            }
            ebpf::LD_ABS_H => {
                name = "ldabsh";
                desc = ldabs_str(name, &insn);
            }
            ebpf::LD_ABS_W => {
                name = "ldabsw";
                desc = ldabs_str(name, &insn);
            }
            ebpf::LD_ABS_DW => {
                name = "ldabsdw";
                desc = ldabs_str(name, &insn);
            }
            ebpf::LD_IND_B => {
                name = "ldindb";
                desc = ldind_str(name, &insn);
            }
            ebpf::LD_IND_H => {
                name = "ldindh";
                desc = ldind_str(name, &insn);
            }
            ebpf::LD_IND_W => {
                name = "ldindw";
                desc = ldind_str(name, &insn);
            }
            ebpf::LD_IND_DW => {
                name = "ldinddw";
                desc = ldind_str(name, &insn);
            }

            ebpf::LD_DW_IMM => {
                insn_ptr += 1;
                let next_insn = ebpf::get_insn(prog, insn_ptr);
                imm = ((insn.imm as u32) as u64 + ((next_insn.imm as u64) << 32)) as i64;
                name = "lddw";
                desc = format!("{name} r{:}, {imm:#x}", insn.dst);
            }

            // BPF_LDX class
            ebpf::LD_B_REG => {
                name = "ldxb";
                desc = ld_reg_str(name, &insn);
            }
            ebpf::LD_H_REG => {
                name = "ldxh";
                desc = ld_reg_str(name, &insn);
            }
            ebpf::LD_W_REG => {
                name = "ldxw";
                desc = ld_reg_str(name, &insn);
            }
            ebpf::LD_DW_REG => {
                name = "ldxdw";
                desc = ld_reg_str(name, &insn);
            }

            // BPF_ST class
            ebpf::ST_B_IMM => {
                name = "stb";
                desc = ld_st_imm_str(name, &insn);
            }
            ebpf::ST_H_IMM => {
                name = "sth";
                desc = ld_st_imm_str(name, &insn);
            }
            ebpf::ST_W_IMM => {
                name = "stw";
                desc = ld_st_imm_str(name, &insn);
            }
            ebpf::ST_DW_IMM => {
                name = "stdw";
                desc = ld_st_imm_str(name, &insn);
            }

            // BPF_STX class
            ebpf::ST_B_REG => {
                name = "stxb";
                desc = st_reg_str(name, &insn);
            }
            ebpf::ST_H_REG => {
                name = "stxh";
                desc = st_reg_str(name, &insn);
            }
            ebpf::ST_W_REG => {
                name = "stxw";
                desc = st_reg_str(name, &insn);
            }
            ebpf::ST_DW_REG => {
                name = "stxdw";
                desc = st_reg_str(name, &insn);
            }
            ebpf::ST_W_XADD => {
                name = "stxxaddw";
                desc = st_reg_str(name, &insn);
            }
            ebpf::ST_DW_XADD => {
                name = "stxxadddw";
                desc = st_reg_str(name, &insn);
            }

            // BPF_ALU class
            ebpf::ADD32_IMM => {
                name = "add32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::ADD32_REG => {
                name = "add32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::SUB32_IMM => {
                name = "sub32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::SUB32_REG => {
                name = "sub32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::MUL32_IMM => {
                name = "mul32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::MUL32_REG => {
                name = "mul32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::DIV32_IMM => {
                name = "div32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::DIV32_REG => {
                name = "div32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::OR32_IMM => {
                name = "or32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::OR32_REG => {
                name = "or32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::AND32_IMM => {
                name = "and32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::AND32_REG => {
                name = "and32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::LSH32_IMM => {
                name = "lsh32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::LSH32_REG => {
                name = "lsh32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::RSH32_IMM => {
                name = "rsh32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::RSH32_REG => {
                name = "rsh32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::NEG32 => {
                name = "neg32";
                desc = format!("{name} r{:}", insn.dst);
            }
            ebpf::MOD32_IMM => {
                name = "mod32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::MOD32_REG => {
                name = "mod32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::XOR32_IMM => {
                name = "xor32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::XOR32_REG => {
                name = "xor32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::MOV32_IMM => {
                name = "mov32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::MOV32_REG => {
                name = "mov32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::ARSH32_IMM => {
                name = "arsh32";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::ARSH32_REG => {
                name = "arsh32";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::LE => {
                name = "le";
                desc = byteswap_str(name, &insn);
            }
            ebpf::BE => {
                name = "be";
                desc = byteswap_str(name, &insn);
            }

            // BPF_ALU64 class
            ebpf::ADD64_IMM => {
                name = "add64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::ADD64_REG => {
                name = "add64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::SUB64_IMM => {
                name = "sub64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::SUB64_REG => {
                name = "sub64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::MUL64_IMM => {
                name = "mul64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::MUL64_REG => {
                name = "mul64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::DIV64_IMM => {
                name = "div64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::DIV64_REG => {
                name = "div64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::OR64_IMM => {
                name = "or64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::OR64_REG => {
                name = "or64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::AND64_IMM => {
                name = "and64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::AND64_REG => {
                name = "and64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::LSH64_IMM => {
                name = "lsh64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::LSH64_REG => {
                name = "lsh64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::RSH64_IMM => {
                name = "rsh64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::RSH64_REG => {
                name = "rsh64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::NEG64 => {
                name = "neg64";
                desc = format!("{name} r{:}", insn.dst);
            }
            ebpf::MOD64_IMM => {
                name = "mod64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::MOD64_REG => {
                name = "mod64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::XOR64_IMM => {
                name = "xor64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::XOR64_REG => {
                name = "xor64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::MOV64_IMM => {
                name = "mov64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::MOV64_REG => {
                name = "mov64";
                desc = alu_reg_str(name, &insn);
            }
            ebpf::ARSH64_IMM => {
                name = "arsh64";
                desc = alu_imm_str(name, &insn);
            }
            ebpf::ARSH64_REG => {
                name = "arsh64";
                desc = alu_reg_str(name, &insn);
            }

            // BPF_JMP class
            ebpf::JA => {
                name = "ja";
                desc = if insn.off >= 0 {
                    format!("{name} +{:#x}", insn.off)
                } else {
                    format!("{name} -{:#x}", -insn.off)
                }
            }
            ebpf::JEQ_IMM => {
                name = "jeq";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JEQ_REG => {
                name = "jeq";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JGT_IMM => {
                name = "jgt";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JGT_REG => {
                name = "jgt";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JGE_IMM => {
                name = "jge";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JGE_REG => {
                name = "jge";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JLT_IMM => {
                name = "jlt";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JLT_REG => {
                name = "jlt";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JLE_IMM => {
                name = "jle";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JLE_REG => {
                name = "jle";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JSET_IMM => {
                name = "jset";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JSET_REG => {
                name = "jset";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JNE_IMM => {
                name = "jne";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JNE_REG => {
                name = "jne";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JSGT_IMM => {
                name = "jsgt";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JSGT_REG => {
                name = "jsgt";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JSGE_IMM => {
                name = "jsge";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JSGE_REG => {
                name = "jsge";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JSLT_IMM => {
                name = "jslt";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JSLT_REG => {
                name = "jslt";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JSLE_IMM => {
                name = "jsle";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JSLE_REG => {
                name = "jsle";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::CALL => {
                name = "call";
                desc = format!("{name} {:#x}", insn.imm);
            }
            ebpf::TAIL_CALL => {
                name = "tail_call";
                desc = name.to_string();
            }
            ebpf::EXIT => {
                name = "exit";
                desc = name.to_string();
            }

            // BPF_JMP32 class
            ebpf::JEQ_IMM32 => {
                name = "jeq32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JEQ_REG32 => {
                name = "jeq32";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JGT_IMM32 => {
                name = "jgt32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JGT_REG32 => {
                name = "jgt32";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JGE_IMM32 => {
                name = "jge32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JGE_REG32 => {
                name = "jge32";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JLT_IMM32 => {
                name = "jlt32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JLT_REG32 => {
                name = "jlt32";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JLE_IMM32 => {
                name = "jle32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JLE_REG32 => {
                name = "jle32";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JSET_IMM32 => {
                name = "jset32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JSET_REG32 => {
                name = "jset32";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JNE_IMM32 => {
                name = "jne32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JNE_REG32 => {
                name = "jne32";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JSGT_IMM32 => {
                name = "jsgt32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JSGT_REG32 => {
                name = "jsgt32";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JSGE_IMM32 => {
                name = "jsge32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JSGE_REG32 => {
                name = "jsge32";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JSLT_IMM32 => {
                name = "jslt32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JSLT_REG32 => {
                name = "jslt32";
                desc = jmp_reg_str(name, &insn);
            }
            ebpf::JSLE_IMM32 => {
                name = "jsle32";
                desc = jmp_imm_str(name, &insn);
            }
            ebpf::JSLE_REG32 => {
                name = "jsle32";
                desc = jmp_reg_str(name, &insn);
            }

            _ => {
                panic!(
                    "[Disassembler] Error: unknown eBPF opcode {:#2x} (insn #{:?})",
                    insn.opc, insn_ptr
                );
            }
        };

        let hl_insn = HLInsn {
            opc: insn.opc,
            name: name.to_string(),
            desc,
            dst: insn.dst,
            src: insn.src,
            off: insn.off,
            imm,
        };

        res.push(hl_insn);

        insn_ptr += 1;
    }
    res
}

/// Disassemble an eBPF program into human-readable instructions and prints it to standard output.
///
/// The program is not checked for errors or inconsistencies.
///
/// # Examples
///
/// ```
/// use rbpf::disassembler;
/// let prog = &[
///     0x07, 0x01, 0x00, 0x00, 0x05, 0x06, 0x00, 0x00,
///     0xb7, 0x02, 0x00, 0x00, 0x32, 0x00, 0x00, 0x00,
///     0xbf, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
///     0xdc, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00,
///     0x87, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
/// ];
/// disassembler::disassemble(prog);
/// # // "\nadd64 r1, 0x605\nmov64 r2, 0x32\nmov64 r1, r0\nbe16 r0\nneg64 r2\nexit"
/// ```
///
/// This will produce the following output:
///
/// ```test
/// add64 r1, 0x605
/// mov64 r2, 0x32
/// mov64 r1, r0
/// be16 r0
/// neg64 r2
/// exit
/// ```
pub fn disassemble(prog: &[u8]) {
    #[cfg(feature = "std")]
    {
        for insn in to_insn_vec(prog) {
            println!("{}", insn.desc);
        }
    }
    #[cfg(not(feature = "std"))]
    {
        for insn in to_insn_vec(prog) {
            log::info!("{}", insn.desc);
        }
    }
}