[GWP-ASan] Crash handler API returns sizeof(collected trace)

[hctim]

Summary

Fix up a slight bug with the crash handler API, where we say that we
return the size of the collected trace (instead of the size of the trace
that's returned) when the return buffer is too small, and the result is
truncated.

Also, as a result, patch up a small uninitialized memory bug.

[hctim]

Apparently static constexpr declarations and initializers go in headers,
but they still require declarations to avoid link-time undefined
reference complaints (except after c++17). Learn something new every day, I guess.

[eugenis]

LGTM

compiler-rt/lib/gwp_asan/tests/backtrace.cpp

109

typo: Dealloc

[hctim]

• Fix up 'dealloc' typo.

compiler-rt/lib/gwp_asan/common.cpp

const char *ErrorToString(const Error &E) {
   case Error::BUFFER_OVERFLOW:
     return "Buffer Overflow";
   case Error::BUFFER_UNDERFLOW:
     return "Buffer Underflow";
   }
   __builtin_trap();
 }
 
+constexpr size_t AllocationMetadata::kStackFrameStorageBytes;
+constexpr size_t AllocationMetadata::kMaxTraceLengthToCollect;
+
 void AllocationMetadata::RecordAllocation(uintptr_t AllocAddr,
                                           size_t AllocSize) {
   Addr = AllocAddr;
   Size = AllocSize;
   IsDeallocated = false;
 
   AllocationTrace.ThreadID = getThreadID();
   DeallocationTrace.TraceSize = 0;

compiler-rt/lib/gwp_asan/crash_handler.cpp

 //===-- crash_handler_interface.cpp -----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "gwp_asan/common.h"
 #include "gwp_asan/stack_trace_compressor.h"
 
 #include <assert.h>
+#include <string.h>
 
 using AllocationMetadata = gwp_asan::AllocationMetadata;
 using Error = gwp_asan::Error;
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 

 uint64_t __gwp_asan_get_allocation_thread_id(
     const gwp_asan::AllocationMetadata *AllocationMeta) {
   return AllocationMeta->AllocationTrace.ThreadID;
 }
 
 size_t __gwp_asan_get_allocation_trace(
     const gwp_asan::AllocationMetadata *AllocationMeta, uintptr_t *Buffer,
     size_t BufferLen) {
-  return gwp_asan::compression::unpack(
+  uintptr_t UncompressedBuffer[AllocationMetadata::kMaxTraceLengthToCollect];
+  size_t UnpackedLength = gwp_asan::compression::unpack(
       AllocationMeta->AllocationTrace.CompressedTrace,
-      AllocationMeta->AllocationTrace.TraceSize, Buffer, BufferLen);
+      AllocationMeta->AllocationTrace.TraceSize, UncompressedBuffer,
+      AllocationMetadata::kMaxTraceLengthToCollect);
+  if (UnpackedLength < BufferLen)
+    BufferLen = UnpackedLength;
+  memcpy(Buffer, UncompressedBuffer, BufferLen * sizeof(*Buffer));
+  return UnpackedLength;
 }
 
 bool __gwp_asan_is_deallocated(
     const gwp_asan::AllocationMetadata *AllocationMeta) {
   return AllocationMeta->IsDeallocated;
 }
 
 uint64_t __gwp_asan_get_deallocation_thread_id(
     const gwp_asan::AllocationMetadata *AllocationMeta) {
   return AllocationMeta->DeallocationTrace.ThreadID;
 }
 
 size_t __gwp_asan_get_deallocation_trace(
     const gwp_asan::AllocationMetadata *AllocationMeta, uintptr_t *Buffer,
     size_t BufferLen) {
-  return gwp_asan::compression::unpack(
+  uintptr_t UncompressedBuffer[AllocationMetadata::kMaxTraceLengthToCollect];
+  size_t UnpackedLength = gwp_asan::compression::unpack(
       AllocationMeta->DeallocationTrace.CompressedTrace,
-      AllocationMeta->DeallocationTrace.TraceSize, Buffer, BufferLen);
+      AllocationMeta->DeallocationTrace.TraceSize, UncompressedBuffer,
+      AllocationMetadata::kMaxTraceLengthToCollect);
+  if (UnpackedLength < BufferLen)
+    BufferLen = UnpackedLength;
+  memcpy(Buffer, UncompressedBuffer, BufferLen * sizeof(*Buffer));
+  return UnpackedLength;
 }
 
 #ifdef __cplusplus
 } // extern "C"
 #endif

compiler-rt/lib/gwp_asan/tests/backtrace.cpp

 //===-- backtrace.cpp -------------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include <string>
 
+#include "gwp_asan/common.h"
 #include "gwp_asan/crash_handler.h"
 #include "gwp_asan/tests/harness.h"
 
 // Optnone to ensure that the calls to these functions are not optimized away,
 // as we're looking for them in the backtraces.
 __attribute((optnone)) void *
 AllocateMemory(gwp_asan::GuardedPoolAllocator &GPA) {
   return GPA.allocate(1);
TEST(Backtrace, Short) {
   EXPECT_EQ(2u, __gwp_asan_get_allocation_trace(&Meta, TraceOutput, 2));
   EXPECT_EQ(TraceOutput[0], 123u);
   EXPECT_EQ(TraceOutput[1], 321u);
 }
 
 TEST(Backtrace, ExceedsStorableLength) {
   gwp_asan::AllocationMetadata Meta;
   Meta.AllocationTrace.RecordBacktrace(
-      [](uintptr_t * /* TraceBuffer */, size_t /* Size */) -> size_t {
-        return SIZE_MAX; // Wow, that's big!
+      [](uintptr_t *TraceBuffer, size_t Size) -> size_t {
+        // Need to inintialise the elements that will be packed.
+        memset(TraceBuffer, 0u, Size * sizeof(*TraceBuffer));
+
+        // Indicate that there were more frames, and we just didn't have enough
+        // room to store them.
+        return Size * 2;
       });
+  // Retrieve a frame from the collected backtrace, make sure it works E2E.
   uintptr_t TraceOutput;
-  EXPECT_EQ(1u, __gwp_asan_get_allocation_trace(&Meta, &TraceOutput, 1));
+  EXPECT_EQ(gwp_asan::AllocationMetadata::kMaxTraceLengthToCollect,
+            __gwp_asan_get_allocation_trace(&Meta, &TraceOutput, 1));
+}
+
+TEST(Backtrace, ExceedsRetrievableAllocLength) {
+  gwp_asan::AllocationMetadata Meta;
+  constexpr size_t kNumFramesToStore = 3u;
+  Meta.AllocationTrace.RecordBacktrace(
+      [](uintptr_t *TraceBuffer, size_t /* Size */) -> size_t {
+        memset(TraceBuffer, kNumFramesToStore,
+               kNumFramesToStore * sizeof(*TraceBuffer));
+        return kNumFramesToStore;
+      });
+  uintptr_t TraceOutput;
+  // Ask for one element, get told that there's `kNumFramesToStore` available.
+  EXPECT_EQ(kNumFramesToStore,
+            __gwp_asan_get_allocation_trace(&Meta, &TraceOutput, 1));
+}
+
+TEST(Backtrace, ExceedsRetrievableDeallocLength) {
+  gwp_asan::AllocationMetadata Meta;
+  constexpr size_t kNumFramesToStore = 3u;
+  Meta.DeallocationTrace.RecordBacktrace(
+      [](uintptr_t *TraceBuffer, size_t /* Size */) -> size_t {
+        memset(TraceBuffer, kNumFramesToStore,
+               kNumFramesToStore * sizeof(*TraceBuffer));
+        return kNumFramesToStore;
+      });
+  uintptr_t TraceOutput;
+  // Ask for one element, get told that there's `kNumFramesToStore` available.
+  EXPECT_EQ(kNumFramesToStore,
+            __gwp_asan_get_deallocation_trace(&Meta, &TraceOutput, 1));
 }