Un-bit-rot mtrace

Fix some compile errors (mtstart depended on C's implicit cast from function pointers to void* and user.h lacked some extern "C" function declarations mtrace needed) and some logic errors (mtstart wasn't happening in idle procs and there was a perplexing mtpause going out of sched).

Un-bit-rot mtrace
523ac2a9 · Austin Clements · 3ab59330 · 523ac2a9 · 523ac2a9 · 523ac2a9
--- a/include/kmtrace.hh
+++ b/include/kmtrace.hh
@@ -7,7 +7,8 @@ struct kstack_tag {
 extern struct kstack_tag kstack_tag[NCPU];

 // Tell mtrace about switching threads/processes
-static inline void mtstart(void *ip, struct proc *p)
+template<typename Ret, typename... Args>
+static inline void mtstart(Ret (*ip)(Args...), struct proc *p)
 {
  unsigned long new_tag;
  int i;

--- a/include/user.h
+++ b/include/user.h
@@ -36,6 +36,8 @@ int setfs(u64 base);
 int stat(char*, struct stat*);
 int fstatat(int dirfd, const char*, struct stat*);
 char* strcpy(char*, const char*);
+char* strncpy(char *s, const char *t, size_t n);
+void* memcpy(void *dst, const void *src, size_t n);
 void* memmove(void*, const void*, size_t);
 char* strchr(const char*, char c);
 int strcmp(const char*, const char*);

--- a/kernel/idle.cc
+++ b/kernel/idle.cc
@@ -8,6 +8,7 @@
 #include "sched.hh"
 #include "percpu.hh"
 #include "wq.hh"
+#include "kmtrace.hh"

 struct idle {
  struct proc *cur;
@@ -89,7 +90,7 @@ idleloop(void)

  // Enabling mtrace calls in scheduler generates many mtrace_call_entrys.
  // mtrace_call_set(1, cpu->id);
-  //mtstart(scheduler, idlep);
+  mtstart(idleloop, myproc());

  sti();
  for (;;) {

--- a/kernel/sched.cc
+++ b/kernel/sched.cc
@@ -84,7 +84,6 @@ sched(void)
  next->set_state(RUNNING);
  next->tsc = rdtsc();

-  mtpause(next);
  if (next->context->rip != (uptr)forkret && 
      next->context->rip != (uptr)threadstub)
  {