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Move CPU core out of RAM. This limits possibilities for self-modifying code hacks, but is cleaner/safer.

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This commit is contained in:
Toby Jaffey 2025-12-09 10:46:29 +00:00
parent 941cd141f4
commit 8c11b45670
3 changed files with 12 additions and 15 deletions
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25
uvm32/uvm32.c
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@ -60,25 +60,22 @@ void uvm32_init(uvm32_state_t *vmst, const uvm32_mapping_t *mappings, uint32_t n
vmst->status = UVM32_STATUS_PAUSED;
UVM32_MEMSET(vmst->memory, 0x00, UVM32_MEMORY_SIZE);
// The core lives at the end of RAM.
vmst->core = (struct MiniRV32IMAState*)(vmst->memory + UVM32_MEMORY_SIZE - sizeof(struct MiniRV32IMAState));
vmst->core->pc = MINIRV32_RAM_IMAGE_OFFSET;
vmst->core.pc = MINIRV32_RAM_IMAGE_OFFSET;
// https://projectf.io/posts/riscv-cheat-sheet/
// setup stack pointer
// la sp, _sstack
// addi sp,sp,-16
vmst->core->regs[2] = (MINIRV32_RAM_IMAGE_OFFSET + UVM32_MEMORY_SIZE - sizeof(struct MiniRV32IMAState)) - 16;
vmst->core->regs[10] = 0x00; //hart ID
vmst->core->regs[11] = 0;
vmst->core->extraflags |= 3; // Machine-mode.
vmst->core.regs[2] = (MINIRV32_RAM_IMAGE_OFFSET + UVM32_MEMORY_SIZE - sizeof(struct MiniRV32IMAState)) - 16;
vmst->core.regs[10] = 0x00; //hart ID
vmst->core.regs[11] = 0;
vmst->core.extraflags |= 3; // Machine-mode.
vmst->mappings = mappings;
vmst->numMappings = numMappings;
}
bool uvm32_load(uvm32_state_t *vmst, uint8_t *rom, int len) {
// RAM needs at least image then MiniRV32IMAState (core)
if (len > UVM32_MEMORY_SIZE - sizeof(struct MiniRV32IMAState)) {
if (len > UVM32_MEMORY_SIZE) {
// too big
return false;
}
@ -143,14 +140,14 @@ uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter)
while(vmst->status == UVM32_STATUS_RUNNING) {
uint64_t elapsedUs = 1;
uint32_t ret;
ret = MiniRV32IMAStep(vmst, vmst->core, vmst->memory, 0, elapsedUs, 1);
ret = MiniRV32IMAStep(vmst, &vmst->core, vmst->memory, 0, elapsedUs, 1);
if (3 == ret) {
const uint32_t syscall = vmst->core->regs[17]; // a7
uint32_t value = vmst->core->regs[10]; // a0
const uint32_t syscall = vmst->core.regs[17]; // a7
uint32_t value = vmst->core.regs[10]; // a0
bool syscall_valid = false;
// on exception we should jump to mtvec, but we handle directly
// and skip over the ecall instruction
vmst->core->pc += 4;
vmst->core.pc += 4;
switch(syscall) {
// inbuilt syscalls
case UVM32_SYSCALL_HALT:
@ -180,7 +177,7 @@ uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter)
break;
case UVM32_SYSCALL_TYP_U32_RD:
// pass link to r1 for user function to update
vmst->ioevt.data.syscall.val.u32p = &vmst->core->regs[11];
vmst->ioevt.data.syscall.val.u32p = &vmst->core.regs[11];
break;
}
vmst->ioevt.typ = UVM32_EVT_SYSCALL;