HZ, log_backtrace updates.

- Decrease HZ when sanitizers are enabled.
- Add a log_backtrace variant that takes rsp, rbp as arguments.

k-hardware.cc

@@ -196,11 +196,18 @@ bool lookup_symbol(uintptr_t addr, const char** name, uintptr_t* start) {
 }
 
 
-// log_backtrace(prefix)
+// log_backtrace(prefix[, rsp, rbp])
 //    Print a backtrace to `log.txt`, each line prefixed by `prefix`.
 
 void log_backtrace(const char* prefix) {
-    uintptr_t rsp = rdrsp(), rbp = rdrbp();
+    log_backtrace(prefix, rdrsp(), rdrbp());
+}
+
+void log_backtrace(const char* prefix, uintptr_t rsp, uintptr_t rbp) {
+    if (rsp != rbp && round_up(rsp, PAGESIZE) == round_down(rbp, PAGESIZE)) {
+        log_printf("%s  warning: possible stack overflow (rsp %p, rbp %p)\n",
+                   rsp, rbp);
+    }
     uintptr_t stack_top = round_up(rsp, PAGESIZE);
     int frame = 1;
     while (rbp >= rsp && rbp < stack_top) {

kernel.hh

@@ -153,7 +153,17 @@ struct yieldstate {
 
 // timekeeping
 
-#define HZ 100                           // number of ticks per second
+// `HZ` defines the number of timer interrupts per second, or ticks.
+// Real kernels typically use 100 or 1000; Chickadee typically uses 100.
+// Exception: Sanitizers slow down the kernel so much that recursive timer
+// interrupts can become a problem, so when sanitizers are on, we reduce the
+// interrupt frequency to 10 per second.
+#if HAVE_SANITIZERS
+# define HZ 10
+#else
+# define HZ 100
+#endif
+
 extern volatile unsigned long ticks;     // number of ticks since boot
 
 
@@ -368,8 +378,10 @@ void log_vprintf(const char* format, va_list val) __attribute__((noinline));
 
 
 // log_backtrace
-//    Print a backtrace to the host's `log.txt` file.
+//    Print a backtrace to the host's `log.txt` file, either for the current
+//    stack or for a given stack range.
 void log_backtrace(const char* prefix = "");
+void log_backtrace(const char* prefix, uintptr_t rsp, uintptr_t rbp);
 
 
 #if HAVE_SANITIZERS