[XRay][compiler-rt] xray::Array Freelist and Iterator Updates

Summary:
We found a bug while working on a benchmark for the profiling mode which
manifests as a segmentation fault in the profiling handler's
implementation. This change adds unit tests which replicate the
issues in isolation.

We've tracked this down as a bug in the implementation of the Freelist
in the `xray::Array` type. This happens when we trim the array by a
number of elements, where we've been incorrectly assigning pointers for
the links in the freelist of chunk nodes. We've taken the chance to add
more debug-only assertions to the code path and allow us to verify these
assumptions in debug builds.

In the process, we also took the opportunity to use iterators to
implement both `front()` and `back()` which exposes a bug in the
iterator decrement operation.  In particular, when we decrement past a
chunk size boundary, we end up moving too far back and reaching the
`SentinelChunk` prematurely.

This change unblocks us to allow for contributing the non-crashing
version of the benchmarks in the test-suite as well.

Reviewers: kpw

Subscribers: mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D48653

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@336644 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 5 deletions

diff --git a/lib/xray/xray_profile_collector.cc b/lib/xray/xray_profile_collector.cc
index 9d057863e..5da8073f5 100644
--- a/lib/xray/xray_profile_collector.cc
+++ b/lib/xray/xray_profile_collector.cc
@@ -16,8 +16,8 @@
 #include "sanitizer_common/sanitizer_common.h"
 #include "sanitizer_common/sanitizer_vector.h"
 #include "xray_profiling_flags.h"
-#include <pthread.h>
 #include <memory>
+#include <pthread.h>
 #include <utility>
 
 namespace __xray {
@@ -55,7 +55,8 @@ void post(const FunctionCallTrie &T, tid_t TId) {
     GlobalAllocators = reinterpret_cast<FunctionCallTrie::Allocators *>(
         InternalAlloc(sizeof(FunctionCallTrie::Allocators)));
     new (GlobalAllocators) FunctionCallTrie::Allocators();
-    *GlobalAllocators = FunctionCallTrie::InitAllocators();
+    *GlobalAllocators = FunctionCallTrie::InitAllocatorsCustom(
+        profilingFlags()->global_allocator_max);
   });
   DCHECK_NE(GlobalAllocators, nullptr);
 
@@ -83,12 +84,11 @@ void post(const FunctionCallTrie &T, tid_t TId) {
     //    and is decoupled from the lifetime management required by the managed
     //    allocator we have in XRay.
     //
-    Item->Trie = reinterpret_cast<FunctionCallTrie *>(
-        InternalAlloc(sizeof(FunctionCallTrie)));
+    Item->Trie = reinterpret_cast<FunctionCallTrie *>(InternalAlloc(
+        sizeof(FunctionCallTrie), nullptr, alignof(FunctionCallTrie)));
     DCHECK_NE(Item->Trie, nullptr);
     new (Item->Trie) FunctionCallTrie(*GlobalAllocators);
   }
-  DCHECK_NE(Item, nullptr);
 
   T.deepCopyInto(*Item->Trie);
 }