1 SimpleScalar3.0: Selected Topics aka Hopefully enough to get you started Michele Co September 10, 2001 Department of Computer Science University of Virginia

2 Outline Overview How to register options How to register stats Gory tour of sim-bpred –Functional vs. behavioral simulation

3 The Big Picture

4 View from a little closer main.c: main() –initializes options and stats databases –register options common to ALL simulators –sim_reg_options() –sim_reg_stats() –sim_check_options() –sim_init() –sim_load_prog() –sim_main() –exit_now() sim-blah.c: –description of how the simulator should behave –definitions of: sim_reg_options() sim_reg_stats() sim_check_options() sim_init() sim_load_prog() sim_main() sim_uninit()

5 Registering Options What is an option? –Commandline specifiable parameter Why register options? –Interface is provided options.c: –opt_reg_int() –opt_reg_uint() –opt_reg_flag() –opt_reg_string() –and many more...

6 Options Example in sim-blah.c: /* maximum number of inst's to execute */ static unsigned int max_insts;... then in sim_reg_options(): opt_reg_uint(odb, /* name of the opt db */ "-max:inst", /* option name */ "maximum number of inst's to execute", /* option description */ &max_insts, /* address of opt var */ 0, /* default value */ TRUE, /* print ? */ NULL /* format */);

7 Registering Stats What’s a stat? –A statistic you wish to track during the simulation Why register a stat? –Interface is provided stats.c: –stat_reg_counter() –stat_reg_formula() –stat_reg_int() –stat_reg_uint() –... and many more

8 Stats Examples In sim_reg_stats(): stat_reg_counter(sdb, /* stats db */ "sim_num_insn", /* option name */ "total number of instructions executed", /* description */ &sim_num_insn, /* addr of stat var */ sim_num_insn, /* initial value */ NULL /* format */); (NOTE: sim_num_insn actually declared in main.c)

9 Stats Examples (2) /* declared outside of sim_reg_stats() */ static counter_t sim_num_branches = 0;... stat_reg_counter(sdb, "sim_num_branches", "total number of branches executed", &sim_num_branches, /* initial value */0, /* format */NULL); stat_reg_formula(sdb, /* stats db */ "sim_IPB",/* opt name */ "instruction per branch", /* desc */ sim_num_insn / sim_num_branches", /* the formula */ NULL/* format */);

10 sim-bpred - The prelude: machine.def DEFINST(,,,, ) #define ADDU_IMPL\ {\ SET_GPR(RD, GPR(RS) + GPR(RT));\ } DEFINST(ADDU, 0x42, "addu", "d,s,t", IntALU, F_ICOMP, DGPR(RD), DNA,DGPR(RS), DGPR(RT), DNA)

11 Branch Definition #define BEQ_IMPL\ {\ SET_TPC(CPC (OFS << 2));\ if (GPR(RS) == GPR(RT))\ SET_NPC(CPC (OFS << 2));\ } DEFINST(BEQ,0x05, "beq","s,t,j", IntALU,F_CTRL|F_COND|F_DIRJMP, DNA, DNA,DGPR(RS), DGPR(RT), DNA)

12 Memory Definition #define LB_IMPL\ {\ sbyte_t _result;\ enum md_fault_type _fault;\ \ _result = READ_BYTE(GPR(BS) + OFS, _fault);\ if (_fault != md_fault_none)\ DECLARE_FAULT(_fault);\ SET_GPR(RT, (word_t)(sword_t)_result);\ } DEFINST(LB,0x20, "lb","t,o(b)", RdPort,F_MEM|F_LOAD|F_DISP, DGPR(RT), DNA,DNA, DGPR(BS), DNA)

13 sim-bpred: macros /* general purpose registers */ #define GPR(N)(regs.regs_R[N]) #define SET_GPR(N,EXPR)(regs.regs_R[N] = (EXPR)) /* floating point registers, L->word, F->single-prec, D->double-prec */ #define FPR_L(N) (regs.regs_F.l[(N)]) #define SET_FPR_L(N,EXPR) (regs.regs_F.l[(N)] = (EXPR)) #define FPR_F(N) (regs.regs_F.f[(N)]) #define SET_FPR_F(N,EXPR) (regs.regs_F.f[(N)] = (EXPR)) #define FPR_D(N) (regs.regs_F.d[(N) >> 1]) #define SET_FPR_D(N,EXPR) (regs.regs_F.d[(N) >> 1] = (EXPR)) /* precise architected memory state help functions */ #define READ_BYTE(SRC, FAULT)\ ((FAULT) = md_fault_none, MEM_READ_BYTE(mem, addr = (SRC)))

14 sim-bpred: main loop while (TRUE) { /* maintain $r0 semantics */ regs.regs_R[MD_REG_ZERO] = 0; /* get the next instruction to execute */ MD_FETCH_INST(inst, mem, regs.regs_PC); /* keep an instruction count */ sim_num_insn++; /* set default reference address and access mode */ addr = 0; is_write = FALSE; /* set default fault - none */ fault = md_fault_none; /* decode the instruction */ MD_SET_OPCODE(op, inst);

15 /* execute the instruction */ switch (op) { #define DEFINST(OP,MSK,NAME,OPFORM,RES,FLAGS,O1,O2,I1,I2,I3)\ case OP:\ SYMCAT(OP,_IMPL);\ break; #define DEFLINK(OP,MSK,NAME,MASK,SHIFT)\ case OP:\ panic("attempted to execute a linking opcode"); #define CONNECT(OP) #define DECLARE_FAULT(FAULT)\ { fault = (FAULT); break; } #include "machine.def" default: panic("attempted to execute a bogus opcode"); } Instruction Execution

16 Sample Expansion of switch() Based on: #define BEQ_IMPL\ {(0)\ SET_TPC(CPC (OFS << 2));(1)\ if (GPR(RS) == GPR(RT))(2)\ SET_NPC(CPC (OFS << 2));(3)\ }(4) DEFINST(BEQ,0x05, "beq","s,t,j", IntALU,F_CTRL|F_COND|F_DIRJMP, DNA, DNA,DGPR(RS), DGPR(RT), DNA) The switch expands to: case BEQ : (generated by switch) { (0) (void)0 ; (1) if ((regs.regs_R[ (inst.b >> 24) ]) == (regs.regs_R[ ((inst.b >> 16) & 0xff) ]) ) (2) (regs.regs_NPC = ( (regs.regs_PC) (((int)(( short)(inst.b & 0xffff))) << 2) )) ; (3) } ; (4) break;(from switch)

17 if (fault != md_fault_none) fatal("fault (%d) 0x%08p", fault, regs.regs_PC); /* Memory Instruction */ if (MD_OP_FLAGS(op) & F_MEM) { sim_num_refs++; if (MD_OP_FLAGS(op) & F_STORE) is_write = TRUE; } /* Control Instruction */ if (MD_OP_FLAGS(op) & F_CTRL) { md_addr_t pred_PC; struct bpred_update_t update_rec; sim_num_branches++;

18 if (pred) { /* get the next predicted fetch address */ pred_PC = bpred_lookup(pred, /* branch addr */regs.regs_PC, /* target */target_PC, /* inst opcode */op, /* call? */MD_IS_CALL(op), /* return? */MD_IS_RETURN(op), /* stash an update ptr */&update_rec, /* stash return stack ptr */&stack_idx); /* valid address returned from branch predictor? */ if (!pred_PC) { /* no predicted taken target, attempt not taken target */ pred_PC = regs.regs_PC + sizeof(md_inst_t); }

19 bpred_update(pred, /* branch addr */regs.regs_PC, /* resolved branch target */regs.regs_NPC, /* taken? */regs.regs_NPC != (regs.regs_PC + sizeof(md_inst_t)), /* pred taken? */pred_PC != (regs.regs_PC + sizeof(md_inst_t)), /* correct pred? */pred_PC == regs.regs_NPC, /* opcode */op, /* predictor update pointer */&update_rec); } /* DLite code deleted here */ /* go to the next instruction */ regs.regs_PC = regs.regs_NPC; regs.regs_NPC += sizeof(md_inst_t); /* finish early? */ if (max_insts && sim_num_insn >= max_insts) return; }