1 files changed, 170 insertions, 0 deletions
diff --git a/lib/esan/esan_sideline_linux.cpp b/lib/esan/esan_sideline_linux.cpp
new file mode 100644
index 000000000..ba4fe62f5
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+++ b/lib/esan/esan_sideline_linux.cpp
@@ -0,0 +1,170 @@
+//===-- esan_sideline_linux.cpp ---------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of EfficiencySanitizer, a family of performance tuners.
+//
+// Support for a separate or "sideline" tool thread on Linux.
+//===----------------------------------------------------------------------===//
+
+#include "sanitizer_common/sanitizer_platform.h"
+#if SANITIZER_LINUX
+
+#include "esan_sideline.h"
+#include "sanitizer_common/sanitizer_atomic.h"
+#include "sanitizer_common/sanitizer_common.h"
+#include "sanitizer_common/sanitizer_linux.h"
+#include <errno.h>
+#include <sched.h>
+#include <sys/prctl.h>
+#include <sys/signal.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+namespace __esan {
+
+static const int SigAltStackSize = 4*1024;
+static const int SidelineStackSize = 4*1024;
+
+// FIXME: we'll need some kind of TLS (can we trust that a pthread key will
+// work in our non-POSIX thread?) to access our data in our signal handler
+// with multiple sideline threads.  For now we assume there is only one
+// sideline thread and we use a dirty solution of a global var.
+static SidelineThread *TheThread;
+
+// We aren't passing SA_NODEFER so the same signal is blocked while here.
+void SidelineThread::handleSidelineSignal(int SigNum, void *SigInfo,
+                                          void *Ctx) {
+  VPrintf(3, "Sideline signal %d\n", SigNum);
+  CHECK_EQ(SigNum, SIGALRM);
+  // See above about needing TLS to avoid this global var.
+  SidelineThread *Thread = TheThread;
+  if (atomic_load(&Thread->SidelineExit, memory_order_relaxed) != 0)
+    return;
+  Thread->sampleFunc(Thread->FuncArg);
+}
+
+void SidelineThread::registerSignal(int SigNum) {
+  __sanitizer_sigaction SigAct;
+  internal_memset(&SigAct, 0, sizeof(SigAct));
+  SigAct.sigaction = handleSidelineSignal;
+  // We do not pass SA_NODEFER as we want to block the same signal.
+  SigAct.sa_flags = SA_ONSTACK | SA_SIGINFO;
+  int Res = internal_sigaction(SigNum, &SigAct, nullptr);
+  CHECK_EQ(Res, 0);
+}
+
+int SidelineThread::runSideline(void *Arg) {
+  VPrintf(1, "Sideline thread starting\n");
+  SidelineThread *Thread = static_cast<SidelineThread*>(Arg);
+
+  // If the parent dies, we want to exit also.
+  internal_prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
+
+  // Set up a signal handler on an alternate stack for safety.
+  InternalScopedBuffer<char> StackMap(SigAltStackSize);
+  struct sigaltstack SigAltStack;
+  SigAltStack.ss_sp = StackMap.data();
+  SigAltStack.ss_size = SigAltStackSize;
+  SigAltStack.ss_flags = 0;
+  internal_sigaltstack(&SigAltStack, nullptr);
+
+  // We inherit the signal mask from the app thread.  In case
+  // we weren't created at init time, we ensure the mask is empty.
+  __sanitizer_sigset_t SigSet;
+  internal_sigfillset(&SigSet);
+  int Res = internal_sigprocmask(SIG_UNBLOCK, &SigSet, nullptr);
+  CHECK_EQ(Res, 0);
+
+  registerSignal(SIGALRM);
+
+  bool TimerSuccess = Thread->adjustTimer(Thread->Freq);
+  CHECK(TimerSuccess);
+
+  // We loop, doing nothing but handling itimer signals.
+  while (atomic_load(&TheThread->SidelineExit, memory_order_relaxed) == 0)
+    sched_yield();
+
+  if (!Thread->adjustTimer(0))
+    VPrintf(1, "Failed to disable timer\n");
+
+  VPrintf(1, "Sideline thread exiting\n");
+  return 0;
+}
+
+bool SidelineThread::launchThread(SidelineFunc takeSample, void *Arg,
+                                  u32 FreqMilliSec) {
+  // This can only be called once.  However, we can't clear a field in
+  // the constructor and check for that here as the constructor for
+  // a static instance is called *after* our module_ctor and thus after
+  // this routine!  Thus we rely on the TheThread check below.
+  CHECK(TheThread == nullptr); // Only one sideline thread is supported.
+  TheThread = this;
+  sampleFunc = takeSample;
+  FuncArg = Arg;
+  Freq = FreqMilliSec;
+  atomic_store(&SidelineExit, 0, memory_order_relaxed);
+
+  // We do without a guard page.
+  Stack = static_cast<char*>(MmapOrDie(SidelineStackSize, "SidelineStack"));
+  // By omitting CLONE_THREAD, the child is in its own thread group and will not
+  // receive any of the application's signals.
+  SidelineId = internal_clone(
+      runSideline, Stack + SidelineStackSize,
+      CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_UNTRACED,
+      this, nullptr /* parent_tidptr */,
+      nullptr /* newtls */, nullptr /* child_tidptr */);
+  int ErrCode;
+  if (internal_iserror(SidelineId, &ErrCode)) {
+    Printf("FATAL: EfficiencySanitizer failed to spawn a thread (code %d).\n",
+           ErrCode);
+    Die();
+    return false; // Not reached.
+  }
+  return true;
+}
+
+bool SidelineThread::joinThread() {
+  VPrintf(1, "Joining sideline thread\n");
+  bool Res = true;
+  atomic_store(&SidelineExit, 1, memory_order_relaxed);
+  while (true) {
+    uptr Status = internal_waitpid(SidelineId, nullptr, __WALL);
+    int ErrCode;
+    if (!internal_iserror(Status, &ErrCode))
+      break;
+    if (ErrCode == EINTR)
+      continue;
+    VPrintf(1, "Failed to join sideline thread (errno %d)\n", ErrCode);
+    Res = false;
+    break;
+  }
+  UnmapOrDie(Stack, SidelineStackSize);
+  return Res;
+}
+
+// Must be called from the sideline thread itself.
+bool SidelineThread::adjustTimer(u32 FreqMilliSec) {
+  CHECK(internal_getpid() == SidelineId);
+  Freq = FreqMilliSec;
+  struct itimerval TimerVal;
+  TimerVal.it_interval.tv_sec = (time_t) Freq / 1000;
+  TimerVal.it_interval.tv_usec = (time_t) (Freq % 1000) * 1000;
+  TimerVal.it_value.tv_sec = (time_t) Freq / 1000;
+  TimerVal.it_value.tv_usec = (time_t) (Freq % 1000) * 1000;
+  // As we're in a different thread group, we cannot use either
+  // ITIMER_PROF or ITIMER_VIRTUAL without taking up scheduled
+  // time ourselves: thus we must use real time.
+  int Res = setitimer(ITIMER_REAL, &TimerVal, nullptr);
+  return (Res == 0);
+}
+
+} // namespace __esan
+
+#endif // SANITIZER_LINUX