[Runtime][Reflection][swift-inspect] Add facilities for tracking and examining backtraces for metadata allocations.

rdar://problem/63674755

Author: mikeash

include/swift/Reflection/ReflectionContext.h

@@ -34,9 +34,10 @@
 #include "swift/Runtime/Unreachable.h"
 
 #include <set>
-#include <vector>
+#include <sstream>
 #include <unordered_map>
 #include <utility>
+#include <vector>
 
 namespace {
 
@@ -794,7 +795,7 @@ class ReflectionContext
   llvm::Optional<std::string> iterateConformances(
     std::function<void(StoredPointer Type, StoredPointer Proto)> Call) {
     std::string ConformancesPointerName =
-      "__swift_debug_protocolConformanceStatePointer";
+        "_swift_debug_protocolConformanceStatePointer";
     auto ConformancesAddrAddr =
       getReader().getSymbolAddress(ConformancesPointerName);
     if (!ConformancesAddrAddr)
@@ -844,9 +845,9 @@ class ReflectionContext
   llvm::Optional<std::string> iterateMetadataAllocations(
     std::function<void (MetadataAllocation<Runtime>)> Call) {
     std::string IterationEnabledName =
-      "__swift_debug_metadataAllocationIterationEnabled";
+        "_swift_debug_metadataAllocationIterationEnabled";
     std::string AllocationPoolPointerName =
-      "__swift_debug_allocationPoolPointer";
+        "_swift_debug_allocationPoolPointer";
 
     auto IterationEnabledAddr =
       getReader().getSymbolAddress(IterationEnabledName);
@@ -922,6 +923,50 @@ class ReflectionContext
     return llvm::None;
   }
 
+  llvm::Optional<std::string> iterateMetadataAllocationBacktraces(
+      std::function<void(StoredPointer, uint32_t, const StoredPointer *)>
+          Call) {
+    std::string BacktraceListName =
+        "_swift_debug_metadataAllocationBacktraceList";
+
+    auto BacktraceListAddr = getReader().getSymbolAddress(BacktraceListName);
+    if (!BacktraceListAddr)
+      return "unable to look up debug variable " + BacktraceListName;
+    auto BacktraceListNextPtr =
+        getReader().readPointer(BacktraceListAddr, sizeof(StoredPointer));
+    if (!BacktraceListNextPtr)
+      return llvm::None;
+
+    auto BacktraceListNext = BacktraceListNextPtr->getResolvedAddress();
+    while (BacktraceListNext) {
+      auto HeaderBytes = getReader().readBytes(
+          RemoteAddress(BacktraceListNext),
+          sizeof(MetadataAllocationBacktraceHeader<Runtime>));
+      auto HeaderPtr =
+          reinterpret_cast<const MetadataAllocationBacktraceHeader<Runtime> *>(
+              HeaderBytes.get());
+      if (HeaderPtr == nullptr) {
+        std::stringstream stream;
+        stream << "unable to read Next pointer 0x" << std::hex
+               << BacktraceListNext.getAddressData();
+        return stream.str();
+      }
+      auto BacktraceAddrPtr =
+          BacktraceListNext +
+          sizeof(MetadataAllocationBacktraceHeader<Runtime>);
+      auto BacktraceBytes =
+          getReader().readBytes(RemoteAddress(BacktraceAddrPtr),
+                                HeaderPtr->Count * sizeof(StoredPointer));
+      auto BacktracePtr =
+          reinterpret_cast<const StoredPointer *>(BacktraceBytes.get());
+
+      Call(HeaderPtr->Allocation, HeaderPtr->Count, BacktracePtr);
+
+      BacktraceListNext = RemoteAddress(HeaderPtr->Next);
+    }
+    return llvm::None;
+  }
+
 private:
   const TypeInfo *getClosureContextInfo(StoredPointer Context,
                                         const ClosureContextInfo &Info) {

include/swift/Runtime/Debug.h

@@ -17,11 +17,13 @@
 #ifndef SWIFT_RUNTIME_DEBUG_HELPERS_H
 #define SWIFT_RUNTIME_DEBUG_HELPERS_H
 
+#include "swift/Runtime/Config.h"
+#include "swift/Runtime/Unreachable.h"
+#include <atomic>
 #include <cstdarg>
 #include <cstdio>
+#include <functional>
 #include <stdint.h>
-#include "swift/Runtime/Config.h"
-#include "swift/Runtime/Unreachable.h"
 
 #ifdef SWIFT_HAVE_CRASHREPORTERCLIENT
 
@@ -145,6 +147,9 @@ void swift_abortDynamicReplacementDisabling();
 void dumpStackTraceEntry(unsigned index, void *framePC,
                          bool shortOutput = false);
 
+SWIFT_RUNTIME_ATTRIBUTE_NOINLINE
+bool withCurrentBacktrace(std::function<void(void **, int)> call);
+
 SWIFT_RUNTIME_ATTRIBUTE_NOINLINE
 void printCurrentBacktrace(unsigned framesToSkip = 1);
 
@@ -237,6 +242,9 @@ bool _swift_debug_metadataAllocationIterationEnabled;
 SWIFT_RUNTIME_STDLIB_SPI
 const void * const _swift_debug_allocationPoolPointer;
 
+SWIFT_RUNTIME_STDLIB_SPI
+std::atomic<const void *> _swift_debug_metadataAllocationBacktraceList;
+
 SWIFT_RUNTIME_STDLIB_SPI
 const void * const _swift_debug_protocolConformanceStatePointer;
 

include/swift/Runtime/Metadata.h

@@ -54,6 +54,13 @@ enum MetadataAllocatorTags : uint16_t {
   GenericValueMetadataTag,
 };
 
+template <typename Runtime> struct MetadataAllocationBacktraceHeader {
+  TargetPointer<Runtime, const void> Next;
+  TargetPointer<Runtime, void> Allocation;
+  uint32_t Count;
+  // Count backtrace pointers immediately follow.
+};
+
 /// The buffer used by a yield-once coroutine (such as the generalized
 /// accessors `read` and `modify`).
 struct YieldOnceBuffer {

include/swift/SwiftRemoteMirror/SwiftRemoteMirror.h

@@ -331,6 +331,28 @@ swift_reflection_ptr_t swift_reflection_allocationMetadataPointer(
   SwiftReflectionContextRef ContextRef,
   swift_metadata_allocation_t Allocation);
 
+/// Backtrace iterator callback passed to
+/// swift_reflection_iterateMetadataAllocationBacktraces
+typedef void (*swift_metadataAllocationIterator)(
+    swift_reflection_ptr_t AllocationPtr, size_t Count,
+    const swift_reflection_ptr_t Ptrs[], void *ContextPtr);
+
+/// Iterate over all recorded metadata allocation backtraces in the process.
+///
+/// Calls the passed in Call function for each recorded backtrace. The function
+/// is passed the number of backtrace entries and an array of those entries, as
+/// pointers. The array is stored from deepest to shallowest, so main() will be
+/// somewhere near the end. This array is valid only for the duration of the
+/// call.
+///
+/// Returns NULL on success. On error, returns a pointer to a C string
+/// describing the error. This pointer remains valid until the next
+/// swift_reflection call on the given context.
+SWIFT_REMOTE_MIRROR_LINKAGE
+const char *swift_reflection_iterateMetadataAllocationBacktraces(
+    SwiftReflectionContextRef ContextRef, swift_metadataAllocationIterator Call,
+    void *ContextPtr);
+
 #ifdef __cplusplus
 } // extern "C"
 #endif

stdlib/public/SwiftRemoteMirror/SwiftRemoteMirror.cpp

@@ -635,3 +635,21 @@ swift_reflection_ptr_t swift_reflection_allocationMetadataPointer(
   NativeAllocation.Size = Allocation.Size;
   return Context->allocationMetadataPointer(NativeAllocation);
 }
+
+const char *swift_reflection_iterateMetadataAllocationBacktraces(
+    SwiftReflectionContextRef ContextRef, swift_metadataAllocationIterator Call,
+    void *ContextPtr) {
+  auto Context = ContextRef->nativeContext;
+  auto Error = Context->iterateMetadataAllocationBacktraces(
+      [&](auto AllocationPtr, auto Count, auto Ptrs) {
+        // Ptrs is an array of StoredPointer, but the callback expects an array
+        // of swift_reflection_ptr_t. Those may are not always the same type.
+        // (For example, swift_reflection_ptr_t can be 64-bit on 32-bit systems,
+        // while StoredPointer is always the pointer size of the target system.)
+        // Convert the array to an array of swift_reflection_ptr_t.
+        std::vector<swift_reflection_ptr_t> ConvertedPtrs{&Ptrs[0],
+                                                          &Ptrs[Count]};
+        Call(AllocationPtr, Count, ConvertedPtrs.data(), ContextPtr);
+      });
+  return convertError(ContextRef, Error);
+}

stdlib/public/runtime/EnvironmentVariables.def

@@ -26,6 +26,10 @@ VARIABLE(SWIFT_DEBUG_ENABLE_METADATA_ALLOCATION_ITERATION, bool, false,
          "Enable additional metadata allocation tracking for swift-inspect to "
          "use.")
 
+VARIABLE(SWIFT_DEBUG_ENABLE_METADATA_BACKTRACE_LOGGING, bool, false,
+         "Enable logging of backtraces for each metadata allocation. Requires "
+         "SWIFT_DEBUG_ENABLE_METADATA_ALLOCATION_ITERATION to be enabled.")
+
 VARIABLE(SWIFT_DEBUG_IMPLICIT_OBJC_ENTRYPOINT, uint8_t, 2,
          "Print warnings when using implicit @objc entrypoints. Set to "
          "desired reporting level, 0-3.")

stdlib/public/runtime/Errors.cpp

@@ -223,8 +223,8 @@ static _Unwind_Reason_Code SwiftUnwindFrame(struct _Unwind_Context *context, voi
 }
 #endif
 
-SWIFT_NOINLINE
-void swift::printCurrentBacktrace(unsigned framesToSkip) {
+SWIFT_ALWAYS_INLINE
+static bool withCurrentBacktraceImpl(std::function<void(void **, int)> call) {
 #if SWIFT_SUPPORTS_BACKTRACE_REPORTING
   constexpr unsigned maxSupportedStackDepth = 128;
   void *addrs[maxSupportedStackDepth];
@@ -237,14 +237,29 @@ void swift::printCurrentBacktrace(unsigned framesToSkip) {
 #else
   int symbolCount = backtrace(addrs, maxSupportedStackDepth);
 #endif
-  for (int i = framesToSkip; i < symbolCount; ++i) {
-    dumpStackTraceEntry(i - framesToSkip, addrs[i]);
-  }
+  call(addrs, symbolCount);
+  return true;
 #else
-  fprintf(stderr, "<backtrace unavailable>\n");
+  return false;
 #endif
 }
 
+SWIFT_NOINLINE
+bool swift::withCurrentBacktrace(std::function<void(void **, int)> call) {
+  return withCurrentBacktraceImpl(call);
+}
+
+SWIFT_NOINLINE
+void swift::printCurrentBacktrace(unsigned framesToSkip) {
+  bool success = withCurrentBacktraceImpl([&](void **addrs, int symbolCount) {
+    for (int i = framesToSkip; i < symbolCount; ++i) {
+      dumpStackTraceEntry(i - framesToSkip, addrs[i]);
+    }
+  });
+  if (!success)
+    fprintf(stderr, "<backtrace unavailable>\n");
+}
+
 #ifdef SWIFT_HAVE_CRASHREPORTERCLIENT
 #include <malloc/malloc.h>
 

stdlib/public/runtime/Metadata.cpp

@@ -5504,12 +5504,19 @@ AllocationPool{PoolRange{InitialAllocationPool.Pool,
 
 bool swift::_swift_debug_metadataAllocationIterationEnabled = false;
 const void * const swift::_swift_debug_allocationPoolPointer = &AllocationPool;
+std::atomic<const void *> swift::_swift_debug_metadataAllocationBacktraceList;
 
 static void checkAllocatorDebugEnvironmentVariable(void *context) {
   _swift_debug_metadataAllocationIterationEnabled
     = runtime::environment::SWIFT_DEBUG_ENABLE_METADATA_ALLOCATION_ITERATION();
-  if (!_swift_debug_metadataAllocationIterationEnabled)
+  if (!_swift_debug_metadataAllocationIterationEnabled) {
+    if (runtime::environment::SWIFT_DEBUG_ENABLE_METADATA_BACKTRACE_LOGGING())
+      swift::warning(RuntimeErrorFlagNone,
+                     "Warning: SWIFT_DEBUG_ENABLE_METADATA_BACKTRACE_LOGGING "
+                     "without SWIFT_DEBUG_ENABLE_METADATA_ALLOCATION_ITERATION "
+                     "has no effect.\n");
     return;
+  }
 
   // Write a PoolTrailer to the end of InitialAllocationPool and shrink
   // the pool accordingly.
@@ -5523,6 +5530,24 @@ static void checkAllocatorDebugEnvironmentVariable(void *context) {
   AllocationPool.store(poolCopy, std::memory_order_relaxed);
 }
 
+static void recordBacktrace(void *allocation) {
+  withCurrentBacktrace([&](void **addrs, int count) {
+    MetadataAllocationBacktraceHeader<InProcess> *record =
+        (MetadataAllocationBacktraceHeader<InProcess> *)malloc(
+            sizeof(*record) + count * sizeof(void *));
+    record->Allocation = allocation;
+    record->Count = count;
+    memcpy(record + 1, addrs, count * sizeof(void *));
+
+    record->Next = _swift_debug_metadataAllocationBacktraceList.load(
+        std::memory_order_relaxed);
+    while (!_swift_debug_metadataAllocationBacktraceList.compare_exchange_weak(
+        record->Next, record, std::memory_order_release,
+        std::memory_order_relaxed))
+      ; // empty
+  });
+}
+
 void *MetadataAllocator::Allocate(size_t size, size_t alignment) {
   assert(Tag != 0);
   assert(alignment <= alignof(void*));
@@ -5582,8 +5607,14 @@ void *MetadataAllocator::Allocate(size_t size, size_t alignment) {
         AllocationHeader *header = (AllocationHeader *)allocation;
         header->Size = size;
         header->Tag = Tag;
-      
-        return allocation + sizeof(AllocationHeader);
+
+        auto *returnedAllocation = allocation + sizeof(AllocationHeader);
+
+        if (runtime::environment ::
+                SWIFT_DEBUG_ENABLE_METADATA_BACKTRACE_LOGGING())
+          recordBacktrace(returnedAllocation);
+
+        return returnedAllocation;
       } else {
         return allocation;
       }

tools/swift-inspect/Sources/swift-inspect/Backtrace.swift

@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftRemoteMirror
+
+struct Backtrace {
+  enum Style {
+    case oneLine
+    case long
+  }
+
+  /// The pointers to the locations in the backtrace. These are stored from
+  /// deepest to shallowest, so main() will be somewhere near the end.
+  var ptrs: [swift_reflection_ptr_t]
+
+  func symbolString(
+    ptr: swift_reflection_ptr_t,
+    inspector: Inspector
+  ) -> String {
+    let symbol = inspector.getSymbol(address: ptr)
+    let name = symbol.name ?? "<unknown>"
+    let library = symbol.library ?? "<unknown>"
+    return "\(hex: ptr) (\(library)) \(name)"
+  }
+
+  func symbolicatedOneLine(inspector: Inspector) -> String {
+    return ptrs.reversed().map {
+      symbolString(ptr: $0, inspector: inspector)
+    }.joined(separator: " | ")
+  }
+
+  func symbolicatedLong(inspector: Inspector) -> String {
+    return ptrs.reversed().enumerated().map {
+      let indent = String(repeating: "  ", count: $0 + 1)
+      return indent + symbolString(ptr: $1, inspector: inspector)
+    }.joined(separator: "\n")
+  }
+
+  func symbolicated(style: Style, inspector: Inspector) -> String {
+    switch style {
+    case .oneLine:
+      return symbolicatedOneLine(inspector: inspector)
+    case .long:
+      return symbolicatedLong(inspector: inspector)
+    }
+  }
+}