From 8c4967cb131d0829b6a1a6e81b152b5667615f17 Mon Sep 17 00:00:00 2001 From: hyenasky Date: Tue, 14 Mar 2023 08:24:49 -0600 Subject: [PATCH] fix several edge case interactions between page faults and instruction execution --- src/cpu.c | 63 ++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 39 insertions(+), 24 deletions(-) diff --git a/src/cpu.c b/src/cpu.c index 1ea1d60..39db575 100644 --- a/src/cpu.c +++ b/src/cpu.c @@ -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) { + // calculate number of bytes for each page + + int bytes_first = 0x1000 - (address & 0x00000FFF); + + 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 - int bytes = 0x1000 - (address & 0x00000FFF); - uint8_t *ptr = vm_findmemory(vm, address, bytes, true); - - while (bytes) { - *ptr = value & 0xFF; + 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--; } } @@ -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; \ } @@ -812,8 +825,8 @@ 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; \ } @@ -821,9 +834,10 @@ 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; \ - 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; \ } @@ -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; \ } @@ -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; \ } @@ -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; \ }