Stack sampling profiler: re-enable stack collection for stacks terminated by leaf functions

base/profiler/win32_stack_frame_unwinder.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/profiler/win32_stack_frame_unwinder.h"
+
+#include "base/containers/hash_tables.h"
+#include "base/memory/singleton.h"
+#include "base/stl_util.h"
+
+namespace base {
+
+// LeafUnwindBlacklist --------------------------------------------------------
+
+namespace {
+
+// Records modules that are known to have functions that violate the Microsoft
+// x64 calling convention and would be dangerous to manually unwind if
+// encountered as the last frame on the call stack.

[cpu_(ooo_6.6-7.5), 2015/08/19 19:07:24]

can you add an example of this kind of function?

[Mike Wittman, 2015/08/19 19:54:41]

Done.

+class LeafUnwindBlacklist {
+ public:
+  static LeafUnwindBlacklist* GetInstance();
+
+  // This function does not allocate memory and is safe to call between
+  // SuspendThread and ResumeThread.
+  bool IsBlacklisted(const void* module) const;
+
+  // Allocates memory. Must be invoked only after ResumeThread, otherwise
+  // RecordStack will eventually deadlock on a heap lock.

[cpu_(ooo_6.6-7.5), 2015/08/19 19:07:24]

we can make RecoardStack allocate from a different heap. This is not difficult
on Windows.

[Mike Wittman, 2015/08/19 19:54:41]

Ah, I didn't mean for this comment to imply that RecordThread allocates memory.
Updated to be clear about the specific deadlock concern.

+  void AddModuleToBlacklist(const void* module);
+
+ private:
+  friend struct DefaultSingletonTraits<LeafUnwindBlacklist>;
+
+  LeafUnwindBlacklist();
+  ~LeafUnwindBlacklist();
+
+  // The set of modules known to have functions that violate the Microsoft x64
+  // calling convention.
+  base::hash_set<const void*> blacklisted_modules_;
+
+  DISALLOW_COPY_AND_ASSIGN(LeafUnwindBlacklist);
+};
+
+// static
+LeafUnwindBlacklist* LeafUnwindBlacklist::GetInstance() {
+  // Leaky for shutdown performance.
+  return Singleton<LeafUnwindBlacklist,
+                   LeakySingletonTraits<LeafUnwindBlacklist>>::get();
+}
+
+bool LeafUnwindBlacklist::IsBlacklisted(const void* module) const {
+  return ContainsKey(blacklisted_modules_, module);
+}
+
+void LeafUnwindBlacklist::AddModuleToBlacklist(const void* module) {
+  CHECK(module);
+  blacklisted_modules_.insert(module);
+}
+
+LeafUnwindBlacklist::LeafUnwindBlacklist() {}
+LeafUnwindBlacklist::~LeafUnwindBlacklist() {}
+
+}  // namespace
+
+// Win32StackFrameUnwinder ----------------------------------------------------
+
+Win32StackFrameUnwinder::UnwindFunctions::~UnwindFunctions() {}
+Win32StackFrameUnwinder::UnwindFunctions::UnwindFunctions() {}
+
+Win32StackFrameUnwinder::Win32UnwindFunctions::Win32UnwindFunctions() {}
+
+PRUNTIME_FUNCTION Win32StackFrameUnwinder::Win32UnwindFunctions::
+LookupFunctionEntry(DWORD64 program_counter, PDWORD64 image_base) {
+#ifdef _WIN64
+  return RtlLookupFunctionEntry(program_counter, image_base, nullptr);
+#else
+  NOTREACHED();
+  return nullptr;
+#endif
+}
+
+void Win32StackFrameUnwinder::Win32UnwindFunctions::VirtualUnwind(
+    DWORD64 image_base,
+    DWORD64 program_counter,
+    PRUNTIME_FUNCTION runtime_function,
+    CONTEXT* context) {
+#ifdef _WIN64
+  void* handler_data;
+  ULONG64 establisher_frame;
+  KNONVOLATILE_CONTEXT_POINTERS nvcontext = {};
+  RtlVirtualUnwind(0, image_base, program_counter, runtime_function,
+                   context, &handler_data, &establisher_frame, &nvcontext);
+#else
+  NOTREACHED();
+#endif
+}
+
+
+Win32StackFrameUnwinder::Win32StackFrameUnwinder()
+    : Win32StackFrameUnwinder(&win32_unwind_functions_) {
+}
+
+Win32StackFrameUnwinder::~Win32StackFrameUnwinder() {
+  if (pending_blacklisted_module_) {
+    LeafUnwindBlacklist::GetInstance()->AddModuleToBlacklist(
+        pending_blacklisted_module_);
+  }
+}
+
+bool Win32StackFrameUnwinder::TryUnwind(CONTEXT* context) {
+#ifdef _WIN64
+  CHECK(!at_top_frame_ || unwind_info_present_for_all_frames_);
+  CHECK(!pending_blacklisted_module_);
+
+  ULONG64 image_base;
+  // Try to look up unwind metadata for the current function.
+  PRUNTIME_FUNCTION runtime_function =
+      unwind_functions_->LookupFunctionEntry(context->Rip, &image_base);
+
+  if (runtime_function) {
+    unwind_functions_->VirtualUnwind(image_base, context->Rip, runtime_function,
+                                     context);
+    at_top_frame_ = false;
+  } else {
+    // RtlLookupFunctionEntry didn't find unwind information. This could mean
+    // the code at the instruction pointer is in:
+    //
+    // 1. a true leaf function (i.e. a function that neither calls a function,
+    //    nor allocates any stack space itself) in which case the return
+    //    address is at RSP, or
+    //
+    // 2. a function that doesn't adhere to the Microsoft x64 calling
+    //    convention, either by not providing the required unwind information,
+    //    or by not having the prologue or epilogue required for unwinding;
+    //    this case has been observed in crash data in injected third party
+    //    DLLs.
+    //
+    // In valid code, case 1 can only occur (by definition) as the last frame
+    // on the stack. This happens in about 5% of observed stacks and can
+    // easily be unwound by popping RSP and using it as the next frame's
+    // instruction pointer.
+    //
+    // Case 2 can occur anywhere on the stack, and attempting to unwind the
+    // stack will result in treating whatever value happens to be on the stack
+    // at RSP as the next frame's instruction pointer. This is certainly wrong
+    // and very likely to lead to crashing by deferencing invalid pointers in
+    // the next RtlVirtualUnwind call.
+    //
+    // If we see case 2 at a location not the last frame, and all the previous
+    // frame had valid unwind information, then this is definitely bad code.
+    // We blacklist the module as untrustable for unwinding if we encounter a
+    // function in it that doesn't have unwind information.
+
+    if (at_top_frame_) {
+      at_top_frame_ = false;
+
+      // We are at the end of the stack. It's very likely that we're in case 1
+      // since the vast majority of code adheres to the Microsoft x64 calling
+      // convention. But there's a small chance we might be unlucky and be in
+      // case 2. If this module is known to have bad code according to the
+      // leaf unwind blacklist, stop here, otherwise manually unwind.
+      if (LeafUnwindBlacklist::GetInstance()->IsBlacklisted(
+              reinterpret_cast<const void*>(image_base))) {
+        return false;
+      }
+
+      context->Rip = context->Rsp;
+      context->Rsp += 8;
+      unwind_info_present_for_all_frames_ = false;
+    } else {
+      // We're not at the end of the stack. This frame is untrustworthy and we
+      // can't safely unwind from here.
+      if (unwind_info_present_for_all_frames_) {
+        // Unwind information was present for all previous frames, so we can
+        // be confident this is case 2. Record the module to be blacklisted.
+        pending_blacklisted_module_ =
+            reinterpret_cast<const void *>(image_base);
+      } else {
+        // We started off on a function without unwind information. It's very
+        // likely that all frames up to this point have been good, and this
+        // frame is case 2. But it's possible that the initial frame was case
+        // 2 but hadn't been blacklisted yet, and we've started to go off into
+        // the weeds. Since we can't be sure, just bail out without
+        // blacklisting the module; chances are we'll later encounter the same
+        // function on a stack with full unwind information.
+      }
+      return false;
+    }
+  }
+
+  return true;
+#else
+  NOTREACHED();
+  return false;
+#endif
+}
+
+Win32StackFrameUnwinder::Win32StackFrameUnwinder(
+    UnwindFunctions* unwind_functions)
+    : at_top_frame_(true),
+      unwind_info_present_for_all_frames_(true),
+      pending_blacklisted_module_(nullptr),
+      unwind_functions_(unwind_functions) {
+}
+
+}  // namespace base