GWP-ASan: Pack stack traces to save space

Make use of the stack trace packing from https://crrev.com/627865 to
reduce memory usage to store stacks on 64-bit systems by ~60% percent. A
GWP-ASan microbenchmark did not show this change to noticably regress
performance.

Bug: 896019, 921237
Change-Id: Iad6e803f18ff12e5fd3079b9821d11bc0918bead
Reviewed-on: https://chromium-review.googlesource.com/c/1448522
Auto-Submit: Vlad Tsyrklevich <vtsyrklevich@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628034}

components/gwp_asan/client/guarded_page_allocator.cc

@@ -17,6 +17,7 @@
 #include "components/crash/core/common/crash_key.h"
 #include "components/gwp_asan/common/allocator_state.h"
 #include "components/gwp_asan/common/crash_key_name.h"
+#include "components/gwp_asan/common/pack_stack_trace.h"
 
 namespace gwp_asan {
 namespace internal {
@@ -174,10 +175,13 @@ void GuardedPageAllocator::RecordAllocationInSlot(size_t slot,
   slots_[slot].alloc_size = size;
   slots_[slot].alloc_ptr = reinterpret_cast<uintptr_t>(ptr);
 
+  void* trace[AllocatorState::kMaxStackFrames];
+  size_t len =
+      base::debug::CollectStackTrace(trace, AllocatorState::kMaxStackFrames);
+  slots_[slot].alloc.trace_len = Pack(reinterpret_cast<uintptr_t*>(trace), len,
+                                      slots_[slot].alloc.packed_trace,
+                                      sizeof(slots_[slot].alloc.packed_trace));
   slots_[slot].alloc.tid = base::PlatformThread::CurrentId();
-  slots_[slot].alloc.trace_len = base::debug::CollectStackTrace(
-      reinterpret_cast<void**>(&slots_[slot].alloc.trace),
-      AllocatorState::kMaxStackFrames);
   slots_[slot].alloc.trace_collected = true;
 
   slots_[slot].dealloc.tid = base::kInvalidThreadId;
@@ -187,10 +191,14 @@ void GuardedPageAllocator::RecordAllocationInSlot(size_t slot,
 }
 
 void GuardedPageAllocator::RecordDeallocationInSlot(size_t slot) {
+  void* trace[AllocatorState::kMaxStackFrames];
+  size_t len =
+      base::debug::CollectStackTrace(trace, AllocatorState::kMaxStackFrames);
+  slots_[slot].dealloc.trace_len =
+      Pack(reinterpret_cast<uintptr_t*>(trace), len,
+           slots_[slot].dealloc.packed_trace,
+           sizeof(slots_[slot].dealloc.packed_trace));
   slots_[slot].dealloc.tid = base::PlatformThread::CurrentId();
-  slots_[slot].dealloc.trace_len = base::debug::CollectStackTrace(
-      reinterpret_cast<void**>(&slots_[slot].dealloc.trace),
-      AllocatorState::kMaxStackFrames);
   slots_[slot].dealloc.trace_collected = true;
 }
 

components/gwp_asan/common/allocator_state.cc

@@ -15,6 +15,7 @@ namespace internal {
 // TODO: Delete out-of-line constexpr defininitons once C++17 is in use.
 constexpr size_t AllocatorState::kGpaMaxPages;
 constexpr size_t AllocatorState::kMaxStackFrames;
+constexpr size_t AllocatorState::kMaxPackedTraceLength;
 
 AllocatorState::AllocatorState() {}
 

components/gwp_asan/common/allocator_state.h

@@ -40,6 +40,9 @@ class AllocatorState {
   static constexpr size_t kGpaMaxPages = 128;
   // Maximum number of stack trace frames to collect.
   static constexpr size_t kMaxStackFrames = 60;
+  // Number of bytes to allocate for packed stack traces. This can hold
+  // approximately kMaxStackFrames under normal conditions.
+  static constexpr size_t kMaxPackedTraceLength = 200;
 
   enum class ErrorType {
     kUseAfterFree = 0,
@@ -65,9 +68,9 @@ class AllocatorState {
       // (De)allocation thread id or base::kInvalidThreadId if no (de)allocation
       // occurred.
       base::PlatformThreadId tid = base::kInvalidThreadId;
-      // Stack trace contents.
-      uintptr_t trace[kMaxStackFrames];
-      // Stack trace length.
+      // Packed stack trace.
+      uint8_t packed_trace[kMaxPackedTraceLength];
+      // Length used to encode the packed stack trace.
       size_t trace_len = 0;
       // Whether a stack trace has been collected for this (de)allocation.
       bool trace_collected = false;

components/gwp_asan/crash_handler/crash_analyzer.cc

@@ -14,6 +14,7 @@
 #include "build/build_config.h"
 #include "components/gwp_asan/common/allocator_state.h"
 #include "components/gwp_asan/common/crash_key_name.h"
+#include "components/gwp_asan/common/pack_stack_trace.h"
 #include "components/gwp_asan/crash_handler/crash.pb.h"
 #include "third_party/crashpad/crashpad/client/annotation.h"
 #include "third_party/crashpad/crashpad/snapshot/cpu_context.h"
@@ -158,12 +159,21 @@ void CrashAnalyzer::ReadAllocationInfo(
     return;
   }
 
-  // On 32-bit platforms we can't copy directly to
+  uintptr_t unpacked_stack_trace[AllocatorState::kMaxPackedTraceLength];
+  size_t unpacked_len =
+      Unpack(slot_info.packed_trace, slot_info.trace_len, unpacked_stack_trace,
+             AllocatorState::kMaxPackedTraceLength);
+  if (!unpacked_len) {
+    DLOG(ERROR) << "Failed to unpack stack trace.";
+    return;
+  }
+
+  // On 32-bit platforms we can't copy directly into
   // proto_info->mutable_stack_trace()->mutable_data().
-  proto_info->mutable_stack_trace()->Resize(slot_info.trace_len, 0);
+  proto_info->mutable_stack_trace()->Resize(unpacked_len, 0);
   uint64_t* output = proto_info->mutable_stack_trace()->mutable_data();
-  for (size_t i = 0; i < slot_info.trace_len; i++)
-    output[i] = slot_info.trace[i];
+  for (size_t i = 0; i < unpacked_len; i++)
+    output[i] = unpacked_stack_trace[i];
 }
 
 }  // namespace internal