[rtsan] Only print out unique stack traces (#110028)

# Why?

In real-time programming, you often have a process or dispatch loop that
is called many, many, many times. Without de-duplication the user will
be drowning in errors.

Introduce a way to only print the stacks one time only, if they have
been seen before

Author: cjappl

compiler-rt/lib/rtsan/rtsan.cpp

@@ -18,6 +18,7 @@
 #include "sanitizer_common/sanitizer_atomic.h"
 #include "sanitizer_common/sanitizer_common.h"
 #include "sanitizer_common/sanitizer_mutex.h"
+#include "sanitizer_common/sanitizer_stackdepot.h"
 #include "sanitizer_common/sanitizer_stacktrace.h"
 
 using namespace __rtsan;
@@ -49,7 +50,30 @@ static auto OnViolationAction(DiagnosticsInfo info) {
   return [info]() {
     IncrementTotalErrorCount();
 
-    PrintDiagnostics(info);
+    BufferedStackTrace stack;
+
+    // We use the unwind_on_fatal flag here because of precedent with other
+    // sanitizers, this action is not necessarily fatal if halt_on_error=false
+    stack.Unwind(info.pc, info.bp, nullptr,
+                 common_flags()->fast_unwind_on_fatal);
+
+    // If in the future we interop with other sanitizers, we will
+    // need to make our own stackdepot
+    StackDepotHandle handle = StackDepotPut_WithHandle(stack);
+
+    const bool is_stack_novel = handle.use_count() == 0;
+
+    // Marked UNLIKELY as if user is runing with halt_on_error=false
+    // we expect a high number of duplicate stacks. We are willing
+    // To pay for the first insertion.
+    if (UNLIKELY(is_stack_novel)) {
+      IncrementUniqueErrorCount();
+
+      PrintDiagnostics(info);
+      stack.Print();
+
+      handle.inc_use_count_unsafe();
+    }
 
     if (flags().halt_on_error)
       Die();

compiler-rt/lib/rtsan/rtsan_diagnostics.cpp

@@ -39,13 +39,6 @@ class Decorator : public __sanitizer::SanitizerCommonDecorator {
 };
 } // namespace
 
-static void PrintStackTrace(uptr pc, uptr bp) {
-  BufferedStackTrace stack{};
-
-  stack.Unwind(pc, bp, nullptr, common_flags()->fast_unwind_on_fatal);
-  stack.Print();
-}
-
 static void PrintError(const Decorator &decorator,
                        const DiagnosticsInfo &info) {
   const auto ErrorTypeStr = [&info]() -> const char * {
@@ -91,5 +84,4 @@ void __rtsan::PrintDiagnostics(const DiagnosticsInfo &info) {
   PrintError(d, info);
   PrintReason(d, info);
   Printf("%s", d.Default());
-  PrintStackTrace(info.pc, info.bp);
 }

compiler-rt/lib/rtsan/rtsan_stats.cpp

@@ -19,17 +19,27 @@ using namespace __sanitizer;
 using namespace __rtsan;
 
 static atomic_uint32_t rtsan_total_error_count{0};
+static atomic_uint32_t rtsan_unique_error_count{0};
 
 void __rtsan::IncrementTotalErrorCount() {
   atomic_fetch_add(&rtsan_total_error_count, 1, memory_order_relaxed);
 }
 
+void __rtsan::IncrementUniqueErrorCount() {
+  atomic_fetch_add(&rtsan_unique_error_count, 1, memory_order_relaxed);
+}
+
 static u32 GetTotalErrorCount() {
   return atomic_load(&rtsan_total_error_count, memory_order_relaxed);
 }
 
+static u32 GetUniqueErrorCount() {
+  return atomic_load(&rtsan_unique_error_count, memory_order_relaxed);
+}
+
 void __rtsan::PrintStatisticsSummary() {
   ScopedErrorReportLock l;
   Printf("RealtimeSanitizer exit stats:\n");
   Printf("    Total error count: %u\n", GetTotalErrorCount());
+  Printf("    Unique error count: %u\n", GetUniqueErrorCount());
 }

compiler-rt/lib/rtsan/rtsan_stats.h

@@ -15,6 +15,7 @@
 namespace __rtsan {
 
 void IncrementTotalErrorCount();
+void IncrementUniqueErrorCount();
 
 void PrintStatisticsSummary();
 

compiler-rt/test/rtsan/deduplicate_errors.cpp

@@ -0,0 +1,39 @@
+// RUN: %clangxx -fsanitize=realtime %s -o %t
+// RUN: env RTSAN_OPTIONS="halt_on_error=false,print_stats_on_exit=true" %run %t 2>&1 | FileCheck %s
+
+// UNSUPPORTED: ios
+
+// Intent: Ensure all errors are deduplicated.
+
+#include <unistd.h>
+
+const int kNumViolations = 10;
+
+void violation() [[clang::nonblocking]] {
+  for (int i = 0; i < kNumViolations; i++)
+    usleep(1);
+}
+
+void violation2() [[clang::nonblocking]] {
+  for (int i = 0; i < kNumViolations; i++)
+    violation();
+}
+
+void double_violation() [[clang::nonblocking]] {
+  violation();
+  violation2();
+}
+
+int main() {
+  violation();        // 1 unique errors here, but 10 total
+  violation2();       // 1 unique errors here, but 100 total
+  double_violation(); // 2 unique errors here, but 110 total
+  return 0;
+}
+
+// CHECK-COUNT-4: ==ERROR:
+// CHECK-NOT: ==ERROR:
+
+// CHECK: RealtimeSanitizer exit stats:
+// CHECK-NEXT: Total error count: 220
+// CHECK-NEXT: Unique error count: 4

compiler-rt/test/rtsan/exit_stats.cpp

@@ -21,3 +21,4 @@ int main() {
 
 // CHECK: RealtimeSanitizer exit stats:
 // CHECK-NEXT: Total error count: 10
+// CHECK-NEXT: Unique error count: 1