1 files changed, 73 insertions, 0 deletions
diff --git a/stage3/watchdog.lua b/stage3/watchdog.lua
new file mode 100644
index 0000000..dac4d57
--- /dev/null
+++ b/stage3/watchdog.lua
@@ -0,0 +1,73 @@
+local regs = {
+	"rax", "rbx",
+	"rcx", "rdx",
+	"rdi", "rsi",
+	"rbp", "rsp",
+	"r8", "r9",
+	"r10", "r11",
+	"r12", "r13",
+	"r14", "r15",
+}
+
+print("global watchdog")
+print("extern rand, watchdog_err")
+
+print("regs_backup: resq 16")
+print("regs_rand: resq 16")
+
+print("watchdog:")
+
+local function iter_regs(f)
+	for i, r in ipairs(regs) do
+		f(i-1, r)
+	end
+end
+
+-- backup registers
+iter_regs(function(i, r) print("mov [regs_backup+" .. (8*i) .. "], " .. r) end)
+
+-- populate random table
+iter_regs(function(i) print("xor rax, rax\ncall rand\nmov [regs_rand+" .. (8*i) .. "], rax") end)
+
+-- read registers from random table
+iter_regs(function(i, r)
+	if r == "rsp" then
+		print("mov [regs_rand+" .. (8*i) .. "], rsp")
+	else
+		print("mov " .. r .. ", [regs_rand+" .. (8*i) .. "]")
+	end
+end)
+
+print(".loop:")
+
+-- wait for interrupts
+print("hlt")
+
+-- check and jump if changed
+iter_regs(function(i, r)
+	print("cmp " .. r .. ", [regs_rand+" .. (8*i) .. "]")
+	print("jne .ch_" .. r)
+end)
+
+print("jmp .loop")
+
+-- write error and return
+iter_regs(function(i, r)
+	print(".ch_" .. r .. ":")
+	print("mov qword[watchdog_err], " .. i)
+	print("mov qword[watchdog_err+8], " .. r)
+	print("mov rax, [regs_rand+" .. (8*i) .. "]")
+	print("mov qword[watchdog_err+16], rax")
+	print("jmp .ret")
+end)
+
+print(".ret:")
+
+-- restore registers
+iter_regs(function(i, r)
+	if r ~= "rsp" then
+		print("mov " .. r .. ", [regs_backup+" .. (8*i) .. "]")
+	end
+end)
+
+print("ret")