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fix several edge case interactions involving page faults #17

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merged 1 commit into from
Mar 14, 2023
Merged

fix several edge case interactions involving page faults #17

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63 changes: 39 additions & 24 deletions src/cpu.c
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Original file line number Diff line number Diff line change
Expand Up @@ -506,32 +506,36 @@ static uint32_t vm_read_across(vm_t *vm, uint32_t address, int size) {
}

void vm_write_across(vm_t *vm, uint32_t address, int size, uint32_t value) {
// write the first page
// calculate number of bytes for each page

int bytes = 0x1000 - (address & 0x00000FFF);
uint8_t *ptr = vm_findmemory(vm, address, bytes, true);
int bytes_first = 0x1000 - (address & 0x00000FFF);

while (bytes) {
*ptr = value & 0xFF;
int address_second = (address + size) & 0xFFFFF000;
int bytes_second = (address + size) & 0x00000FFF;

// make sure both pages are resident before doing any writing

uint8_t *ptr_first = vm_findmemory(vm, address, bytes_first, true);
uint8_t *ptr_second = vm_findmemory(vm, address_second, bytes_second, true);

// write the first page

while (bytes_first) {
*ptr_first = value & 0xFF;
value >>= 8;

ptr++;
bytes--;
ptr_first++;
bytes_first--;
}

// write the second page

bytes = (address + size) & 0x00000FFF;
address = (address + size) & 0xFFFFF000;

ptr = vm_findmemory(vm, address, bytes, true);

while (bytes) {
*ptr = value & 0xFF;
while (bytes_second) {
*ptr_second = value & 0xFF;
value >>= 8;

ptr++;
bytes--;
ptr_second++;
bytes_second--;
}
}

Expand Down Expand Up @@ -790,9 +794,18 @@ static void vm_skipparam(vm_t *vm, uint32_t size, uint8_t prtype) {
break; \
}

// make sure NOT to update the stack pointer until the full instruction has
// been read, and the target has been written. otherwise a pagefault halfway
// through could wreak havoc.

#define VM_IMPL_POP(_size, _vm_target, _vm_pop) { \
VM_PRELUDE_1(_size); \
_vm_target(vm, instr.source, _vm_pop(vm)); \
uint32_t oldsp = vm->pointer_stack; \
uint32_t val = _vm_pop(vm); \
uint32_t newsp = vm->pointer_stack; \
vm->pointer_stack = oldsp; \
_vm_target(vm, instr.source, val); \
vm->pointer_stack = newsp; \
break; \
}

Expand All @@ -812,18 +825,19 @@ static void vm_skipparam(vm_t *vm, uint32_t size, uint8_t prtype) {
VM_PRELUDE_1(_size); \
_type v = _vm_source_stay(vm, instr.source); \
_type x = ~v; \
vm->flag_zero = x == 0; \
_vm_target(vm, instr.source, x); \
vm->flag_zero = x == 0; \
break; \
}

#define VM_IMPL_INC(_size, _type, _vm_source_stay, _vm_target, _oper) { \
VM_PRELUDE_1(_size); \
_type v = _vm_source_stay(vm, instr.source); \
_type x; \
vm->flag_carry = _oper(v, 1, &x); \
vm->flag_zero = x == 0; \
bool carry = _oper(v, 1, &x); \
_vm_target(vm, instr.source, x); \
vm->flag_carry = carry; \
vm->flag_zero = x == 0; \
break; \
}

Expand All @@ -832,9 +846,10 @@ static void vm_skipparam(vm_t *vm, uint32_t size, uint8_t prtype) {
_type a = (_type) _vm_source(vm, instr.source); \
_type b = (_type) _vm_source_stay(vm, instr.target); \
_type x; \
vm->flag_carry = _oper(b, a, &x); \
vm->flag_zero = x == 0; \
bool carry = _oper(b, a, &x); \
_vm_target(vm, instr.target, (_type_target) x); \
vm->flag_carry = carry; \
vm->flag_zero = x == 0; \
break; \
}

Expand All @@ -843,8 +858,8 @@ static void vm_skipparam(vm_t *vm, uint32_t size, uint8_t prtype) {
_type a = (_type) _vm_source(vm, instr.source); \
_type b = (_type) _vm_source_stay(vm, instr.target); \
_type x = _oper(b, a); \
vm->flag_zero = x == 0; \
_vm_target(vm, instr.target, (_type_target) x); \
vm->flag_zero = x == 0; \
break; \
}

Expand All @@ -857,8 +872,8 @@ static void vm_skipparam(vm_t *vm, uint32_t size, uint8_t prtype) {
break; \
} \
_type x = _oper(b, a); \
vm->flag_zero = x == 0; \
_vm_target(vm, instr.target, (_type_target) x); \
vm->flag_zero = x == 0; \
break; \
}

Expand Down