tsan: don't instrument __attribute__((naked)) functions

[AntonBikineev]

Summary

Naked functions must not have compiler generated prologues/epilogues, hence no instrumentation is needed for them.

I was not sure whether to disable instrumentation for an entire function or only for prologues/epilogues (tsan_func_entry/tsan_func_exit), but I assumed that the latter would probably be incorrect. Please let me if you think this is wrong.

FWIW, from the C/C++ frontend point of view, naked functions can only contain inline assembly.

[AntonBikineev]

Ping

[kcc]

The code is ok, but I'd like to see an ACK from Dmitry.

[AntonBikineev]

Thanks for taking a look!

llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp

 }
 
 bool ThreadSanitizer::sanitizeFunction(Function &F,
                                        const TargetLibraryInfo &TLI) {
   // This is required to prevent instrumenting call to __tsan_init from within
   // the module constructor.
   if (F.getName() == kTsanModuleCtorName)
     return false;
+  // Naked functions can not have prologue/epilogue
+  // (__tsan_func_entry/__tsan_func_exit) generated, so don't instrument them at
+  // all.
+  if (F.hasFnAttribute(Attribute::Naked))
+    return false;
   initialize(*F.getParent());
   SmallVector<Instruction*, 8> AllLoadsAndStores;
   SmallVector<Instruction*, 8> LocalLoadsAndStores;
   SmallVector<Instruction*, 8> AtomicAccesses;
   SmallVector<Instruction*, 8> MemIntrinCalls;
   bool Res = false;
   bool HasCalls = false;
   bool SanitizeFunction = F.hasFnAttribute(Attribute::SanitizeThread);

llvm/test/Instrumentation/ThreadSanitizer/tsan_basic.ll

 ; CHECK-NOT: __tsan_write
 ; CHECK: ret
 define void @SwiftErrorCall(i8** swifterror) sanitize_thread {
   %swifterror_addr = alloca swifterror i8*
   store i8* null, i8** %0
   call void @SwiftError(i8** %0)
   ret void
 }
+
+; CHECK-LABEL: @NakedTest(i32* %a)
+; CHECK-NEXT:   call void @foo()
+; CHECK-NEXT:   %tmp1 = load i32, i32* %a, align 4
+; CHECK-NEXT:   ret i32 %tmp1
+define i32 @NakedTest(i32* %a) naked sanitize_thread {
+  call void @foo()
+  %tmp1 = load i32, i32* %a, align 4
+  ret i32 %tmp1
+}
+
+declare void @foo() nounwind
+
 ; CHECK: define internal void @tsan.module_ctor()
 ; CHECK: call void @__tsan_init()