path: root/src/core/arm/dyncom/arm_dyncom_thumb.cpp

// Copyright 2012 Michael Kang, 2014 Citra Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

// We can provide simple Thumb simulation by decoding the Thumb instruction into its corresponding
// ARM instruction, and using the existing ARM simulator.

#include "core/arm/dyncom/arm_dyncom_thumb.h"

// Decode a 16bit Thumb instruction.  The instruction is in the low 16-bits of the tinstr field,
// with the following Thumb instruction held in the high 16-bits.  Passing in two Thumb instructions
// allows easier simulation of the special dual BL instruction.

tdstate thumb_translate(u32 addr, u32 instr, u32* ainstr, u32* inst_size) {
    tdstate valid = t_uninitialized;
    ARMword tinstr = instr;

    // The endian should be judge here
    if((addr & 0x3) != 0)
        tinstr = instr >> 16;
    else
        tinstr &= 0xFFFF;

    *ainstr = 0xDEADC0DE; // Debugging to catch non updates

    switch ((tinstr & 0xF800) >> 11) {
    case 0: // LSL
    case 1: // LSR
    case 2: // ASR
        *ainstr = 0xE1B00000                    // base opcode
            | ((tinstr & 0x1800) >> (11 - 5))   // shift type
            |((tinstr & 0x07C0) << (7 - 6))     // imm5
            |((tinstr & 0x0038) >> 3)           // Rs
            |((tinstr & 0x0007) << 12);         // Rd
        break;

    case 3: // ADD/SUB
        {
            static const ARMword subset[4] = {
                0xE0900000,     // ADDS Rd,Rs,Rn
                0xE0500000,     // SUBS Rd,Rs,Rn
                0xE2900000,     // ADDS Rd,Rs,#imm3
                0xE2500000      // SUBS Rd,Rs,#imm3
            };
            // It is quicker indexing into a table, than performing switch or conditionals:
            *ainstr = subset[(tinstr & 0x0600) >> 9]    // base opcode
                |((tinstr & 0x01C0) >> 6)               // Rn or imm3
                |((tinstr & 0x0038) << (16 - 3))        // Rs
                |((tinstr & 0x0007) << (12 - 0));       // Rd
        }
        break;

    case 4: // MOV
    case 5: // CMP
    case 6: // ADD
    case 7: // SUB
        {
            static const ARMword subset[4] = {
                0xE3B00000,     // MOVS Rd,#imm8
                0xE3500000,     // CMP  Rd,#imm8
                0xE2900000,     // ADDS Rd,Rd,#imm8
                0xE2500000,     // SUBS Rd,Rd,#imm8
            };

            *ainstr = subset[(tinstr & 0x1800) >> 11]   // base opcode
                |((tinstr & 0x00FF) >> 0)               // imm8
                |((tinstr & 0x0700) << (16 - 8))        // Rn
                |((tinstr & 0x0700) << (12 - 8));       // Rd
        }
        break;

    case 8: // Arithmetic and high register transfers

        // TODO: Since the subsets for both Format 4 and Format 5 instructions are made up of
        // different ARM encodings, we could save the following conditional, and just have one
        // large subset

        if ((tinstr & (1 << 10)) == 0) {
            enum otype {
                t_norm,
                t_shift,
                t_neg,
                t_mul
            };

            static const struct {
                ARMword opcode;
                otype type;
            } subset[16] = {
                { 0xE0100000, t_norm },     // ANDS Rd,Rd,Rs
                { 0xE0300000, t_norm },     // EORS Rd,Rd,Rs
                { 0xE1B00010, t_shift },    // MOVS Rd,Rd,LSL Rs
                { 0xE1B00030, t_shift },    // MOVS Rd,Rd,LSR Rs
                { 0xE1B00050, t_shift },    // MOVS Rd,Rd,ASR Rs
                { 0xE0B00000, t_norm },     // ADCS Rd,Rd,Rs
                { 0xE0D00000, t_norm },     // SBCS Rd,Rd,Rs
                { 0xE1B00070, t_shift },    // MOVS Rd,Rd,ROR Rs
                { 0xE1100000, t_norm },     // TST  Rd,Rs
                { 0xE2700000, t_neg },      // RSBS Rd,Rs,#0
                { 0xE1500000, t_norm },     // CMP  Rd,Rs
                { 0xE1700000, t_norm },     // CMN  Rd,Rs
                { 0xE1900000, t_norm },     // ORRS Rd,Rd,Rs
                { 0xE0100090, t_mul },      // MULS Rd,Rd,Rs
                { 0xE1D00000, t_norm },     // BICS Rd,Rd,Rs
                { 0xE1F00000, t_norm }      // MVNS Rd,Rs
            };

            *ainstr = subset[(tinstr & 0x03C0) >> 6].opcode; // base

            switch (subset[(tinstr & 0x03C0) >> 6].type) {
            case t_norm:
                *ainstr |= ((tinstr & 0x0007) << 16)    // Rn
                    |((tinstr & 0x0007) << 12)          // Rd
                    |((tinstr & 0x0038) >> 3);          // Rs
                break;
            case t_shift:
                *ainstr |= ((tinstr & 0x0007) << 12)    // Rd
                    |((tinstr & 0x0007) >> 0)           // Rm
                    |((tinstr & 0x0038) << (8 - 3));    // Rs
                break;
            case t_neg:
                *ainstr |= ((tinstr & 0x0007) << 12)    // Rd
                    |((tinstr & 0x0038) << (16 - 3));   // Rn
                break;
            case t_mul:
                *ainstr |= ((tinstr & 0x0007) << 16)    // Rd
                    |((tinstr & 0x0007) << 8)           // Rs
                    |((tinstr & 0x0038) >> 3);          // Rm
                break;
            }
        } else {
            ARMword Rd = ((tinstr & 0x0007) >> 0);
            ARMword Rs = ((tinstr & 0x0038) >> 3);

            if (tinstr & (1 << 7))
                Rd += 8;
            if (tinstr & (1 << 6))
                Rs += 8;

            switch ((tinstr & 0x03C0) >> 6) {
            case 0x1:                           // ADD Rd,Rd,Hs
            case 0x2:                           // ADD Hd,Hd,Rs
            case 0x3:                           // ADD Hd,Hd,Hs
                *ainstr = 0xE0800000            // base
                    | (Rd << 16)                // Rn
                    |(Rd << 12)                 // Rd
                    |(Rs << 0);                 // Rm
                break;
            case 0x5:                           // CMP Rd,Hs
            case 0x6:                           // CMP Hd,Rs
            case 0x7:                           // CMP Hd,Hs
                *ainstr = 0xE1500000            // base
                    | (Rd << 16)                // Rn
                    |(Rd << 12)                 // Rd
                    |(Rs << 0);                 // Rm
                break;
            case 0x9:                           // MOV Rd,Hs
            case 0xA:                           // MOV Hd,Rs
            case 0xB:                           // MOV Hd,Hs
                *ainstr = 0xE1A00000            // base
                    | (Rd << 16)                // Rn
                    |(Rd << 12)                 // Rd
                    |(Rs << 0);                 // Rm
                break;
            case 0xC:                           // BX Rs
            case 0xD:                           // BX Hs
                *ainstr = 0xE12FFF10            // base
                    | ((tinstr & 0x0078) >> 3); // Rd
                break;
            case 0x0:                           // UNDEFINED
            case 0x4:                           // UNDEFINED
            case 0x8:                           // UNDEFINED
                valid = t_undefined;
                break;
            case 0xE:                           // BLX
            case 0xF:                           // BLX
                *ainstr = 0xE1200030            // base
                    | (Rs << 0);                // Rm
                break;
            }
        }
        break;

    case 9: // LDR Rd,[PC,#imm8]
        *ainstr = 0xE59F0000                    // base
            | ((tinstr & 0x0700) << (12 - 8))   // Rd
            |((tinstr & 0x00FF) << (2 - 0));    // off8 
        break;

    case 10:
    case 11:
        // TODO: Format 7 and Format 8 perform the same ARM encoding, so the following could be
        // merged into a single subset, saving on the following boolean:

        if ((tinstr & (1 << 9)) == 0) {
            static const ARMword subset[4] = {
                0xE7800000, // STR  Rd,[Rb,Ro]
                0xE7C00000, // STRB Rd,[Rb,Ro]
                0xE7900000, // LDR  Rd,[Rb,Ro]
                0xE7D00000  // LDRB Rd,[Rb,Ro]
            };

            *ainstr = subset[(tinstr & 0x0C00) >> 10]   // base
                |((tinstr & 0x0007) << (12 - 0))        // Rd
                |((tinstr & 0x0038) << (16 - 3))        // Rb
                |((tinstr & 0x01C0) >> 6);              // Ro

        } else {
            static const ARMword subset[4] = {
                0xE18000B0, // STRH  Rd,[Rb,Ro]
                0xE19000D0, // LDRSB Rd,[Rb,Ro]
                0xE19000B0, // LDRH  Rd,[Rb,Ro]
                0xE19000F0  // LDRSH Rd,[Rb,Ro]
            };
            *ainstr = subset[(tinstr & 0x0C00) >> 10]   // base
                |((tinstr & 0x0007) << (12 - 0))        // Rd
                |((tinstr & 0x0038) << (16 - 3))        // Rb
                |((tinstr & 0x01C0) >> 6);              // Ro
        }
        break;

    case 12: // STR Rd,[Rb,#imm5]
    case 13: // LDR Rd,[Rb,#imm5]
    case 14: // STRB Rd,[Rb,#imm5]
    case 15: // LDRB Rd,[Rb,#imm5]
        {
            static const ARMword subset[4] = {
                0xE5800000,     // STR  Rd,[Rb,#imm5]
                0xE5900000,     // LDR  Rd,[Rb,#imm5]
                0xE5C00000,     // STRB Rd,[Rb,#imm5]
                0xE5D00000      // LDRB Rd,[Rb,#imm5]
            };
            // The offset range defends on whether we are transferring a byte or word value:
            *ainstr = subset[(tinstr & 0x1800) >> 11]   // base
                |((tinstr & 0x0007) << (12 - 0))        // Rd
                |((tinstr & 0x0038) << (16 - 3))        // Rb
                |((tinstr & 0x07C0) >> (6 - ((tinstr & (1 << 12)) ? 0 : 2))); // off5
        }
        break;

    case 16: // STRH Rd,[Rb,#imm5]
    case 17: // LDRH Rd,[Rb,#imm5]
        *ainstr = ((tinstr & (1 << 11))         // base
               ? 0xE1D000B0                     // LDRH
               : 0xE1C000B0)                    // STRH
            |((tinstr & 0x0007) << (12 - 0))    // Rd
            |((tinstr & 0x0038) << (16 - 3))    // Rb
            |((tinstr & 0x01C0) >> (6 - 1))     // off5, low nibble
            |((tinstr & 0x0600) >> (9 - 8));    // off5, high nibble
        break;

    case 18: // STR Rd,[SP,#imm8]
    case 19: // LDR Rd,[SP,#imm8]
        *ainstr = ((tinstr & (1 << 11))         // base
               ? 0xE59D0000                     // LDR
               : 0xE58D0000)                    // STR
            |((tinstr & 0x0700) << (12 - 8))    // Rd
            |((tinstr & 0x00FF) << 2);          // off8
        break;

    case 20: // ADD Rd,PC,#imm8
    case 21: // ADD Rd,SP,#imm8

        if ((tinstr & (1 << 11)) == 0) {

            // NOTE: The PC value used here should by word aligned. We encode shift-left-by-2 in the
            // rotate immediate field, so no shift of off8 is needed.

            *ainstr = 0xE28F0F00                    // base
                | ((tinstr & 0x0700) << (12 - 8))   // Rd
                |(tinstr & 0x00FF);                 // off8
        } else {
            // We encode shift-left-by-2 in the rotate immediate field, so no shift of off8 is needed.
            *ainstr = 0xE28D0F00                    // base
                | ((tinstr & 0x0700) << (12 - 8))   // Rd
                |(tinstr & 0x00FF);                 // off8
        }
        break;

    case 22:
    case 23:
        if ((tinstr & 0x0F00) == 0x0000) {
            // NOTE: The instruction contains a shift left of 2 equivalent (implemented as ROR #30):
            *ainstr = ((tinstr & (1 << 7))  // base
                   ? 0xE24DDF00             // SUB
                   : 0xE28DDF00)            // ADD
                |(tinstr & 0x007F);         // off7
        } else if ((tinstr & 0x0F00) == 0x0e00)
            *ainstr = 0xEF000000 | 0x180000; // base | BKPT mask
        else {
            static const ARMword subset[4] = {
                0xE92D0000, // STMDB sp!,{rlist}
                0xE92D4000, // STMDB sp!,{rlist,lr}
                0xE8BD0000, // LDMIA sp!,{rlist}
                0xE8BD8000  // LDMIA sp!,{rlist,pc}
            };
            *ainstr = subset[((tinstr & (1 << 11)) >> 10) | ((tinstr & (1 << 8)) >> 8)] // base
                |(tinstr & 0x00FF); // mask8
        }
        break;

    case 24: //  STMIA
    case 25: //  LDMIA
        *ainstr = ((tinstr & (1 << 11))         // base
               ? 0xE8B00000                     // LDMIA
               : 0xE8A00000)                    // STMIA
            |((tinstr & 0x0700) << (16 - 8))    // Rb
            |(tinstr & 0x00FF);                 // mask8
        break;

    case 26: // Bcc
    case 27: // Bcc/SWI
        if ((tinstr & 0x0F00) == 0x0F00) {
            // Format 17 : SWI
            *ainstr = 0xEF000000;
            // Breakpoint must be handled specially.
            if ((tinstr & 0x00FF) == 0x18)
                *ainstr |= ((tinstr & 0x00FF) << 16);
            // New breakpoint value.  See gdb/arm-tdep.c
            else if ((tinstr & 0x00FF) == 0xFE)
                *ainstr |= 0x180000; // base |= BKPT mask
            else
                *ainstr |= (tinstr & 0x00FF);
        } else if ((tinstr & 0x0F00) != 0x0E00)
            valid = t_branch;
        else //  UNDEFINED : cc=1110(AL) uses different format
            valid = t_undefined;

        break;

    case 28: // B
        valid = t_branch;
        break;

    case 29:
        if(tinstr & 0x1)
            valid = t_undefined;
        else
            valid = t_branch;
        break;

    case 30: // BL instruction 1

        // There is no single ARM instruction equivalent for this Thumb instruction. To keep the
        // simulation simple (from the user perspective) we check if the following instruction is
        // the second half of this BL, and if it is we simulate it immediately

        valid = t_branch;
        break;

    case 31: // BL instruction 2

        // There is no single ARM instruction equivalent for this instruction. Also, it should only
        // ever be matched with the fmt19 "BL instruction 1" instruction. However, we do allow the
        // simulation of it on its own, with undefined results if r14 is not suitably initialised.

        valid = t_branch;
        break;
    }

    *inst_size = 2;

    return valid;
}