allocate exception memory from a per-proc bufer, so that we can

handle out-of-memory situations without requiring memory allocation.

allocate exception memory from a per-proc bufer, so that we can
4c16796a · Nickolai Zeldovich · d53f7567 · 4c16796a · 4c16796a · 4c16796a
--- a/include/proc.hh
+++ b/include/proc.hh
@@ -85,6 +85,9 @@ struct proc : public rcu_freed {
  int uaccess_;
  u8 __cxa_eh_global[16];

+  std::atomic<int> exception_inuse;
+  u8 exception_buf[256];
+
  static proc* alloc();
  void         set_state(procstate_t s);
  procstate_t  get_state(void) const { return state_; }

--- a/kernel/cpprt.cc
+++ b/kernel/cpprt.cc
@@ -149,6 +149,7 @@ namespace __cxxabiv1 {

 static char malloc_buf[65536];
 static std::atomic<size_t> malloc_idx;
+static bool malloc_proc = false;

 extern "C" void* malloc(size_t);
 void*
@@ -161,6 +162,12 @@ malloc(size_t n)
    return &malloc_buf[myoff];
  }

+  if (malloc_proc) {
+    assert(n <= sizeof(myproc()->exception_buf));
+    assert(cmpxch(&myproc()->exception_inuse, 0, 1));
+    return myproc()->exception_buf;
+  }
+
  u64* p = (u64*) kmalloc(n+8, "cpprt malloc");
  *p = n;
  return p+1;
@@ -173,6 +180,11 @@ free(void* vp)
  if (vp >= malloc_buf && vp < malloc_buf + sizeof(malloc_buf))
    return;

+  if (vp == myproc()->exception_buf) {
+    myproc()->exception_inuse = 0;
+    return;
+  }
+
  u64* p = (u64*) vp;
  kmfree(p-1, p[-1]+8);
 }
@@ -217,6 +229,7 @@ initcpprt(void)
    throw 5;
  } catch (int& x) {
    assert(x == 5);
+    malloc_proc = true;
    return;
  }


--- a/kernel/proc.cc
+++ b/kernel/proc.cc
@@ -43,7 +43,7 @@ proc::proc(int npid) :
  ftable(0), cwd(0), tsc(0), curcycles(0), cpuid(0), epoch(0),
  cpu_pin(0), runq(0), oncv(0), cv_wakeup(0),
  user_fs_(0), unmap_tlbreq_(0), in_exec_(0), uaccess_(0),
-  state_(EMBRYO)
+  exception_inuse(0), state_(EMBRYO)
 {
  snprintf(lockname, sizeof(lockname), "cv:proc:%d", pid);
  initlock(&lock, lockname+3, LOCKSTAT_PROC);