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Implement jump table, labels in code
This commit is contained in:
Peter Evans
parent
9000245002
commit
26529f77ab
@ -4,10 +4,14 @@
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#include "vm_bits.h"
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#include "vm_segment.h"
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extern int mos6502_dis_expected_bytes(vm_8bit);
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extern bool mos6502_dis_is_jump_label(int);
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extern int mos6502_dis_expected_bytes(int);
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extern int mos6502_dis_opcode(FILE *, vm_segment *, int);
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extern void mos6502_dis_instruction(FILE *, int);
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extern void mos6502_dis_operand(FILE *, int, vm_16bit);
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extern void mos6502_dis_jump_label(vm_16bit, int, int);
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extern void mos6502_dis_jump_unlabel(int);
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extern void mos6502_dis_label(FILE *, int);
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extern void mos6502_dis_operand(FILE *, int, int, vm_16bit);
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extern void mos6502_dis_scan(FILE *, vm_segment *, int, int);
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#endif
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@ -1,6 +1,8 @@
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#ifndef _MOS6502_H_
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#define _MOS6502_H_
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#include <stdbool.h>
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#include "vm_bits.h"
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#include "vm_segment.h"
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@ -111,6 +113,7 @@ typedef vm_8bit (*mos6502_address_resolver)(mos6502 *);
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*/
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typedef void (*mos6502_instruction_handler)(mos6502 *, vm_8bit);
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extern bool mos6502_would_jump(int);
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extern int mos6502_cycles(mos6502 *, vm_8bit);
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extern int mos6502_instruction(vm_8bit);
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extern mos6502 *mos6502_create();
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@ -6,6 +6,7 @@
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* stack, etc.
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*/
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#include <stdbool.h>
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#include <stdio.h>
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#include <stdlib.h>
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@ -401,3 +402,24 @@ mos6502_read_byte(mos6502 *cpu)
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return byte;
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}
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/*
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* Return true if the given instruction would require that we jump
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* to somewhere else in the program.
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*/
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inline bool
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mos6502_would_jump(int inst_code)
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{
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return
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inst_code == BCC ||
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inst_code == BCS ||
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inst_code == BEQ ||
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inst_code == BMI ||
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inst_code == BNE ||
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inst_code == BPL ||
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inst_code == BRK ||
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inst_code == BVC ||
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inst_code == BVS ||
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inst_code == JMP ||
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inst_code == JSR;
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}
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@ -4,9 +4,14 @@
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* Disassembly of the mos6502 machine code into an assembly notation.
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*/
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#include <stdbool.h>
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#include "mos6502.h"
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#include "mos6502.dis.h"
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#include "mos6502.enums.h"
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static vm_8bit jump_table[MOS6502_MEMSIZE];
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static char *instruction_strings[] = {
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"ADC",
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"AND",
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@ -74,8 +79,10 @@ static char *instruction_strings[] = {
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* type.
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*/
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void
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mos6502_dis_operand(FILE *stream, int addr_mode, vm_16bit value)
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mos6502_dis_operand(FILE *stream, int address, int addr_mode, vm_16bit value)
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{
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int rel_address;
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switch (addr_mode) {
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case ACC:
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break;
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@ -94,7 +101,11 @@ mos6502_dis_operand(FILE *stream, int addr_mode, vm_16bit value)
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case IMP:
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break;
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case IND:
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fprintf(stream, "($%04X)", value);
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if (jump_table[value]) {
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mos6502_dis_label(stream, value);
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} else {
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fprintf(stream, "($%04X)", value);
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}
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break;
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case IDX:
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fprintf(stream, "($%02X,X)", value);
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@ -103,9 +114,12 @@ mos6502_dis_operand(FILE *stream, int addr_mode, vm_16bit value)
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fprintf(stream, "($%02X),Y", value);
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break;
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case REL:
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// FIXME: we need some kind of table of jumps and branches
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// we make, so that we can come up with some labels to use.
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fprintf(stream, "(REL)");
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rel_address = address + value;
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if (value > 127) {
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rel_address -= 256;
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}
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mos6502_dis_label(stream, rel_address);
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break;
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case ZPG:
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fprintf(stream, "$%02X", value);
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@ -191,6 +205,7 @@ mos6502_dis_opcode(FILE *stream, vm_segment *segment, int address)
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vm_8bit opcode;
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vm_16bit operand;
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int addr_mode;
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int inst_code;
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int expected;
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// The next byte is assumed to be the opcode we work with.
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@ -201,6 +216,9 @@ mos6502_dis_opcode(FILE *stream, vm_segment *segment, int address)
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addr_mode = mos6502_addr_mode(opcode);
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expected = mos6502_dis_expected_bytes(addr_mode);
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// The specific instruction we mean to execute
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inst_code = mos6502_instruction(opcode);
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// The operand itself defaults to zero... in cases where this
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// doesn't change, the instruction related to the opcode will
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// probably not even use it.
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@ -233,25 +251,50 @@ mos6502_dis_opcode(FILE *stream, vm_segment *segment, int address)
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break;
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}
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// Let's print out to the stream what we have so far. First, we
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// indent by four spaces.
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fprintf(stream, " ");
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// Print out the instruction code that our opcode represents.
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mos6502_dis_instruction(stream, mos6502_instruction(opcode));
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if (expected) {
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// Let's "tab" over; each instruction code is 3 characters, so let's
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// move over 5 spaces (4 spaces indent + 1, just to keep everything
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// aligned by 4-character boundaries).
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fprintf(stream, " ");
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// Print out the operand given the proper address mode.
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mos6502_dis_operand(stream, mos6502_addr_mode(opcode), operand);
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// If the stream is NULL, we're doing some kind of lookahead.
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// Furthermore, if this is an instruction that would switch control
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// to a different spot in the program, then let's label this in the
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// jump table.
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if (stream == NULL && mos6502_would_jump(inst_code)) {
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mos6502_dis_jump_label(operand, address, addr_mode);
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}
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// And let's terminate the line.
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fprintf(stream, "\n");
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// It's totally possible that we are not expected to print out the
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// contents of our inspection of the opcode. (For example, we may
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// just want to set the jump table in a lookahead operation.)
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if (stream) {
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// Hey! We might have a label at this position in the code. If
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// so, let's print out the label.
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if (jump_table[address]) {
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// This will print out just the label itself.
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mos6502_dis_label(stream, address);
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// But to actually define the label, we need a colon to
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// complete the notation. (We don't _need_ a newline, but it
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// looks nicer to my arbitrary sensibilities. Don't @ me!)
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fprintf(stream, ":\n");
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}
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// Let's print out to the stream what we have so far. First, we
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// indent by four spaces.
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fprintf(stream, " ");
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// Print out the instruction code that our opcode represents.
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mos6502_dis_instruction(stream, inst_code);
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if (expected) {
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// Let's "tab" over; each instruction code is 3 characters, so let's
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// move over 5 spaces (4 spaces indent + 1, just to keep everything
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// aligned by 4-character boundaries).
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fprintf(stream, " ");
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// Print out the operand given the proper address mode.
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mos6502_dis_operand(stream, address, addr_mode, operand);
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}
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// And let's terminate the line.
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fprintf(stream, "\n");
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}
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// The expected number of bytes here is for the operand, but we need
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// to add one for the opcode to return the true number that this
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@ -266,3 +309,37 @@ mos6502_dis_scan(FILE *stream, vm_segment *segment, int pos, int end)
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pos += mos6502_dis_opcode(stream, segment, pos);
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}
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}
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void
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mos6502_dis_jump_label(vm_16bit operand, int address, int addr_mode)
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{
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int jump_loc = operand;
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if (addr_mode == REL) {
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jump_loc = address + operand;
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if (operand > 127) {
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jump_loc -= 256;
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}
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}
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jump_table[jump_loc] = 1;
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}
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inline void
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mos6502_dis_label(FILE *stream, int address)
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{
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fprintf(stream, "ADDR_%d", address);
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}
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inline void
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mos6502_dis_jump_unlabel(int address)
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{
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jump_table[address] = 0;
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}
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inline bool
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mos6502_dis_is_jump_label(int address)
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{
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return jump_table[address] == 1;
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}
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@ -66,37 +66,51 @@ TestSuite(mos6502_dis, .init = setup, .fini = teardown);
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Test(mos6502_dis, operand)
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{
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mos6502_dis_operand(stream, ABS, 0x1234);
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mos6502_dis_operand(stream, 0, ABS, 0x1234);
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assert_buf("$1234");
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mos6502_dis_operand(stream, ABX, 0x1234);
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mos6502_dis_operand(stream, 0, ABX, 0x1234);
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assert_buf("$1234,X");
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mos6502_dis_operand(stream, ABY, 0x1234);
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mos6502_dis_operand(stream, 0, ABY, 0x1234);
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assert_buf("$1234,Y");
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mos6502_dis_operand(stream, IMM, 0x12);
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mos6502_dis_operand(stream, 0, IMM, 0x12);
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assert_buf("#$12");
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mos6502_dis_operand(stream, IND, 0x1234);
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// For JMPs and JSRs (and BRKs), this should be a label and not a
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// literal value. So we need to test both the literal and
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// jump-labeled version.
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mos6502_dis_operand(stream, 0, IND, 0x1234);
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assert_buf("($1234)");
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mos6502_dis_operand(stream, IDX, 0x12);
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mos6502_dis_jump_label(0x1234, 0, IND);
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mos6502_dis_operand(stream, 0, IND, 0x1234);
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assert_buf("ADDR_4660"); // = 0x1234
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// Let's undo our label above...
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mos6502_dis_jump_unlabel(0x1234);
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mos6502_dis_operand(stream, 0, IDX, 0x12);
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assert_buf("($12,X)");
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mos6502_dis_operand(stream, IDY, 0x34);
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mos6502_dis_operand(stream, 0, IDY, 0x34);
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assert_buf("($34),Y");
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mos6502_dis_operand(stream, ZPG, 0x34);
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mos6502_dis_operand(stream, 0, ZPG, 0x34);
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assert_buf("$34");
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mos6502_dis_operand(stream, ZPX, 0x34);
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mos6502_dis_operand(stream, 0, ZPX, 0x34);
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assert_buf("$34,X");
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mos6502_dis_operand(stream, ZPY, 0x34);
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mos6502_dis_operand(stream, 0, ZPY, 0x34);
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assert_buf("$34,Y");
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// These should both end up printing nothing
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mos6502_dis_operand(stream, ACC, 0);
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mos6502_dis_operand(stream, 0, ACC, 0);
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assert_buf("");
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mos6502_dis_operand(stream, IMP, 0);
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mos6502_dis_operand(stream, 0, IMP, 0);
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assert_buf("");
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// FIXME: this is intentionally "broken" until we can implement a
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// jump table
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mos6502_dis_operand(stream, REL, 0x34);
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assert_buf("(REL)");
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// Test a forward jump (operand < 128)
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mos6502_dis_operand(stream, 500, REL, 52);
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assert_buf("ADDR_552");
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// Test a backward jump (operand >= 128)
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mos6502_dis_operand(stream, 500, REL, 152);
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assert_buf("ADDR_396");
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}
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Test(mos6502_dis, instruction)
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@ -218,3 +232,20 @@ Test(mos6502_dis, scan)
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" JMP ($1234)\n"
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);
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}
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Test(mos6502_dis, jump_label)
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{
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cr_assert_eq(mos6502_dis_is_jump_label(123), false);
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mos6502_dis_jump_label(123, 0, IND);
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cr_assert_eq(mos6502_dis_is_jump_label(123), true);
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mos6502_dis_jump_unlabel(123);
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cr_assert_eq(mos6502_dis_is_jump_label(123), false);
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}
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Test(mos6502_dis, label)
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{
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mos6502_dis_label(stream, 123);
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assert_buf("ADDR_123");
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}
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