[PATCH] D108202: [tsan] Add support for disable_sanitizer_instrumentation attribute

[Alexander Potapenko via Phabricator via cfe-commits]

glider created this revision.
glider added a reviewer: melver.
Herald added subscribers: jfb, hiraditya.
glider requested review of this revision.
Herald added projects: clang, LLVM.
Herald added subscribers: llvm-commits, cfe-commits.

Unlike __attribute__((no_sanitize("thread"))), this one will cause TSan
to skip the entire function during instrumentation.

Depends on https://reviews.llvm.org/D108029


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D108202

Files:
  clang/docs/ThreadSanitizer.rst
  clang/test/CodeGen/sanitize-thread-disable.c
  llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp


Index: llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp
+++ llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp
@@ -563,6 +563,12 @@
   // all.
   if (F.hasFnAttribute(Attribute::Naked))
     return false;
+
+  // __attribute__(disable_sanitizer_instrumentation) prevents all kinds of
+  // instrumentation.
+  if (F.hasFnAttribute(Attribute::DisableSanitizerInstrumentation))
+    return false;
+
   initialize(*F.getParent());
   SmallVector<InstructionInfo, 8> AllLoadsAndStores;
   SmallVector<Instruction*, 8> LocalLoadsAndStores;
Index: clang/test/CodeGen/sanitize-thread-disable.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/sanitize-thread-disable.c
@@ -0,0 +1,57 @@
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck -check-prefixes CHECK,WITHOUT %s
+// RUN: %clang_cc1 -emit-llvm -o - %s -fsanitize=thread | FileCheck -check-prefixes CHECK,TSAN %s
+
+#include <stdatomic.h>
+
+// Instrumented function.
+// TSan inserts calls to __tsan_func_entry() and __tsan_func_exit() to prologue/epilogue.
+// Non-atomic loads are instrumented with __tsan_readXXX(), atomic loads - with
+// __tsan_atomicXXX_load().
+//
+// CHECK: @instrumented1
+// TSAN: call void @__tsan_func_entry
+// WITHOUT-NOT: call void @__tsan_func_entry
+// TSAN: call void @__tsan_read4
+// WITHOUT-NOT: call void @__tsan_read4
+// TSAN: call i32 @__tsan_atomic32_load
+// WITHOUT-NOT: call i32 @__tsan_atomic32_load
+// TSAN: call void @__tsan_func_exit
+// WITHOUT-NOT: call void @__tsan_func_exit
+// CHECK: ret i32
+int instrumented1(int *a, _Atomic int *b) {
+  return *a + atomic_load(b);
+}
+
+// Function with no_sanitize("thread").
+// TSan only inserts instrumentation necessary to prevent false positives: calls are inserted for
+// function entry/exit and atomics, but not plain memory accesses.
+//
+// CHECK: @no_false_positives1
+// TSAN: call void @__tsan_func_entry
+// WITHOUT-NOT: call void @__tsan_func_entry
+// TSAN-NOT: call void @__tsan_read4
+// WITHOUT-NOT: call void @__tsan_read4
+// TSAN: call i32 @__tsan_atomic32_load
+// WITHOUT-NOT: call i32 @__tsan_atomic32_load
+// TSAN: call void @__tsan_func_exit
+// WITHOUT-NOT: call void @__tsan_func_exit
+// CHECK: ret i32
+__attribute__((no_sanitize("thread"))) int no_false_positives1(int *a, _Atomic int *b) {
+  return *a + atomic_load(b);
+}
+
+// Function with disable_sanitizer_instrumentation: no instrumentation at all.
+//
+// CHECK: @no_instrumentation1
+// TSAN-NOT: call void @__tsan_func_entry
+// WITHOUT-NOT: call void @__tsan_func_entry
+// TSAN-NOT: call void @__tsan_read4
+// WITHOUT-NOT: call void @__tsan_read4
+// TSAN-NOT: call i32 @__tsan_atomic32_load
+// WITHOUT-NOT: call i32 @__tsan_atomic32_load
+// TSAN-NOT: call void @__tsan_func_exit
+// WITHOUT-NOT: call void @__tsan_func_exit
+// CHECK: ret i32
+__attribute__((disable_sanitizer_instrumentation)) int no_instrumentation1(int *a, _Atomic int *b) {
+  return *a + atomic_load(b);
+}
Index: clang/docs/ThreadSanitizer.rst
===================================================================
--- clang/docs/ThreadSanitizer.rst
+++ clang/docs/ThreadSanitizer.rst
@@ -100,6 +100,15 @@
 traces.  This attribute may not be supported by other compilers, so we suggest
 to use it together with ``__has_feature(thread_sanitizer)``.
 
+``__attribute__((disable_sanitizer_instrumentation))``
+--------------------------------------------------------
+
+The ``disable_sanitizer_instrumentation`` attribute can be applied to a certain
+function to prevent all kinds of instrumentation. This attribute overrides
+``no_sanitize("thread")`` and may introduce false positives, so it should
+be used with care, e.g. when the user wants to ensure critical code does not
+have unexpected side effects.
+
 Ignorelist
 ----------
 


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