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Properly handle indirect addresses

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This commit is contained in:
Peter Evans 2017-12-30 21:48:16 -06:00
parent b7211f43c2
commit 7e142e2736
2 changed files with 31 additions and 9 deletions
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2
include/mos6502.dis.h
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@ -8,7 +8,7 @@ extern bool mos6502_dis_is_jump_label(int);
extern int mos6502_dis_expected_bytes(int);
extern int mos6502_dis_opcode(FILE *, vm_segment *, int);
extern void mos6502_dis_instruction(FILE *, int);
extern void mos6502_dis_jump_label(vm_16bit, int, int);
extern void mos6502_dis_jump_label(vm_16bit, vm_segment *, int, int);
extern void mos6502_dis_jump_unlabel(int);
extern void mos6502_dis_label(FILE *, int);
extern void mos6502_dis_operand(FILE *, int, int, vm_16bit);

30
src/mos6502.dis.c
View File

@ -256,7 +256,7 @@ mos6502_dis_opcode(FILE *stream, vm_segment *segment, int address)
// to a different spot in the program, then let's label this in the
// jump table.
if (stream == NULL && mos6502_would_jump(inst_code)) {
mos6502_dis_jump_label(operand, address, addr_mode);
mos6502_dis_jump_label(operand, segment, address, addr_mode);
}
// It's totally possible that we are not expected to print out the
@ -311,16 +311,38 @@ mos6502_dis_scan(FILE *stream, vm_segment *segment, int pos, int end)
}
void
mos6502_dis_jump_label(vm_16bit operand, int address, int addr_mode)
mos6502_dis_jump_label(vm_16bit operand,
vm_segment *segment,
int address,
int addr_mode)
{
int jump_loc = operand;
int jump_loc;
if (addr_mode == REL) {
switch (addr_mode) {
// With indirect address mode, the address we want to jump to is
// not the literal operand, but a 16-bit address that is
// _pointed to_ by the address represented by the operand. Think
// of the operand as a kind of double pointer, or just re-watch
// Inception.
case IND:
jump_loc = vm_segment_get(segment, operand) << 8;
jump_loc |= vm_segment_get(segment, operand + 1);
break;
// In relative address mode, the jump location will be a
// number -- well -- relative to the address. If the 8th bit
// of the operand is 1, then we treat the number as a
// negative; otherwise, positive or zero.
case REL:
jump_loc = address + operand;
if (operand > 127) {
jump_loc -= 256;
}
break;
default:
return;
}
jump_table[jump_loc] = 1;