[compiler-rt] r334064 - [XRay][compiler-rt] Refactor recursion guard for Basic and FDR Mode
Dean Michael Berris via llvm-commits
llvm-commits at lists.llvm.org
Tue Jun 5 23:07:48 PDT 2018
Author: dberris
Date: Tue Jun 5 23:07:48 2018
New Revision: 334064
URL: http://llvm.org/viewvc/llvm-project?rev=334064&view=rev
Log:
[XRay][compiler-rt] Refactor recursion guard for Basic and FDR Mode
Summary:
This change extracts the recursion guard implementation from FDR Mode
and updates it to do the following:
- Do the atomic operation correctly to be signal-handler safe.
- Make it usable in both FDR and Basic Modes.
Before this change, the recursion guard relied on an unsynchronised read
and write on a volatile thread-local. A signal handler could then run in
between the read and the write, and then be able to run instrumented
code as part of the signal handling. Using an atomic exchange instead
fixes that by doing a proper mutual exclusion even in the presence of
signal handling.
Reviewers: kpw, eizan, jfb
Reviewed By: eizan
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D47696
Added:
compiler-rt/trunk/lib/xray/xray_recursion_guard.h
Modified:
compiler-rt/trunk/lib/xray/tests/CMakeLists.txt
compiler-rt/trunk/lib/xray/xray_basic_logging.cc
compiler-rt/trunk/lib/xray/xray_fdr_logging.cc
Modified: compiler-rt/trunk/lib/xray/tests/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/tests/CMakeLists.txt?rev=334064&r1=334063&r2=334064&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/tests/CMakeLists.txt (original)
+++ compiler-rt/trunk/lib/xray/tests/CMakeLists.txt Tue Jun 5 23:07:48 2018
@@ -35,6 +35,7 @@ set(XRAY_IMPL_FILES
../../xray_profile_collector.h
../../xray_profiler_flags.cc
../../xray_profiler_flags.h
+ ../../xray_recursion_guard.h
../../xray_segmented_array.h
../../xray_trampoline_powerpc64.cc
../../xray_tsc.h
Modified: compiler-rt/trunk/lib/xray/xray_basic_logging.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/xray_basic_logging.cc?rev=334064&r1=334063&r2=334064&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/xray_basic_logging.cc (original)
+++ compiler-rt/trunk/lib/xray/xray_basic_logging.cc Tue Jun 5 23:07:48 2018
@@ -29,6 +29,7 @@
#include "sanitizer_common/sanitizer_allocator_internal.h"
#include "sanitizer_common/sanitizer_libc.h"
#include "xray/xray_records.h"
+#include "xray_recursion_guard.h"
#include "xray_basic_flags.h"
#include "xray_basic_logging.h"
#include "xray_defs.h"
@@ -70,7 +71,7 @@ static atomic_uint8_t BasicInitialized{0
BasicLoggingOptions GlobalOptions;
-thread_local volatile bool RecursionGuard = false;
+thread_local atomic_uint8_t Guard{0};
static uint64_t thresholdTicks() XRAY_NEVER_INSTRUMENT {
static uint64_t TicksPerSec = probeRequiredCPUFeatures()
@@ -165,10 +166,9 @@ void InMemoryRawLog(int32_t FuncId, XRay
// Use a simple recursion guard, to handle cases where we're already logging
// and for one reason or another, this function gets called again in the same
// thread.
- if (RecursionGuard)
+ RecursionGuard G(Guard);
+ if (!G)
return;
- RecursionGuard = true;
- auto ExitGuard = at_scope_exit([] { RecursionGuard = false; });
uint8_t CPU = 0;
uint64_t TSC = ReadTSC(CPU);
@@ -276,10 +276,9 @@ void InMemoryRawLogWithArg(int32_t FuncI
// Then we write the "we have an argument" record.
InMemoryRawLog(FuncId, Type, ReadTSC);
- if (RecursionGuard)
+ RecursionGuard G(Guard);
+ if (!G)
return;
- RecursionGuard = true;
- auto ExitGuard = at_scope_exit([] { RecursionGuard = false; });
// And from here on write the arg payload.
XRayArgPayload R;
Modified: compiler-rt/trunk/lib/xray/xray_fdr_logging.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/xray_fdr_logging.cc?rev=334064&r1=334063&r2=334064&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/xray_fdr_logging.cc (original)
+++ compiler-rt/trunk/lib/xray/xray_fdr_logging.cc Tue Jun 5 23:07:48 2018
@@ -28,6 +28,7 @@
#include "sanitizer_common/sanitizer_common.h"
#include "xray/xray_interface.h"
#include "xray/xray_records.h"
+#include "xray_recursion_guard.h"
#include "xray_buffer_queue.h"
#include "xray_defs.h"
#include "xray_fdr_flags.h"
@@ -122,33 +123,6 @@ static ThreadLocalData &getThreadLocalDa
return TLD;
}
-namespace {
-
-class RecursionGuard {
- volatile bool &Running;
- const bool Valid;
-
-public:
- explicit RecursionGuard(volatile bool &R) : Running(R), Valid(!R) {
- if (Valid)
- Running = true;
- }
-
- RecursionGuard(const RecursionGuard &) = delete;
- RecursionGuard(RecursionGuard &&) = delete;
- RecursionGuard &operator=(const RecursionGuard &) = delete;
- RecursionGuard &operator=(RecursionGuard &&) = delete;
-
- explicit operator bool() const { return Valid; }
-
- ~RecursionGuard() noexcept {
- if (Valid)
- Running = false;
- }
-};
-
-} // namespace
-
static void writeNewBufferPreamble(tid_t Tid,
timespec TS) XRAY_NEVER_INSTRUMENT {
static constexpr int InitRecordsCount = 2;
@@ -553,7 +527,7 @@ static void endBufferIfFull() XRAY_NEVER
}
}
-thread_local volatile bool Running = false;
+thread_local atomic_uint8_t Running{0};
/// Here's where the meat of the processing happens. The writer captures
/// function entry, exit and tail exit points with a time and will create
@@ -574,7 +548,7 @@ static void processFunctionHook(int32_t
// handleArg0 to happen at any given time.
RecursionGuard Guard{Running};
if (!Guard) {
- DCHECK(Running == true && "RecursionGuard is buggy!");
+ DCHECK(atomic_load_relaxed(&Running) && "RecursionGuard is buggy!");
return;
}
Added: compiler-rt/trunk/lib/xray/xray_recursion_guard.h
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/xray_recursion_guard.h?rev=334064&view=auto
==============================================================================
--- compiler-rt/trunk/lib/xray/xray_recursion_guard.h (added)
+++ compiler-rt/trunk/lib/xray/xray_recursion_guard.h Tue Jun 5 23:07:48 2018
@@ -0,0 +1,57 @@
+//===-- xray_recursion_guard.h ---------------------------------*- 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 XRay, a dynamic runtime instrumentation system.
+//
+//===----------------------------------------------------------------------===//
+#ifndef XRAY_XRAY_RECURSION_GUARD_H
+#define XRAY_XRAY_RECURSION_GUARD_H
+
+#include "sanitizer_common/sanitizer_atomic.h"
+
+namespace __xray {
+
+/// The RecursionGuard is useful for guarding against signal handlers which are
+/// also potentially calling XRay-instrumented functions. To use the
+/// RecursionGuard, you'll typically need a thread_local atomic_uint8_t:
+///
+/// thread_local atomic_uint8_t Guard{0};
+///
+/// // In a handler function:
+/// void handleArg0(int32_t F, XRayEntryType T) {
+/// RecursionGuard G(Guard);
+/// if (!G)
+/// return; // Failed to acquire the guard.
+/// ...
+/// }
+///
+class RecursionGuard {
+ atomic_uint8_t &Running;
+ const bool Valid;
+
+public:
+ explicit inline RecursionGuard(atomic_uint8_t &R)
+ : Running(R), Valid(!atomic_exchange(&R, 1, memory_order_acq_rel)) {}
+
+ inline RecursionGuard(const RecursionGuard &) = delete;
+ inline RecursionGuard(RecursionGuard &&) = delete;
+ inline RecursionGuard &operator=(const RecursionGuard &) = delete;
+ inline RecursionGuard &operator=(RecursionGuard &&) = delete;
+
+ explicit inline operator bool() const { return Valid; }
+
+ inline ~RecursionGuard() noexcept {
+ if (Valid)
+ atomic_store(&Running, 0, memory_order_release);
+ }
+};
+
+} // namespace __xray
+
+#endif // XRAY_XRAY_RECURSION_GUARD_H
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