[rtsan] Handle attributed IR function declarations

[davidtrevelyan]

Addresses #169377.

Previously, the RealtimeSanitizer pass only handled attributed function definitions in IR, and we have recently found that attributed function declarations caused it to crash. To fix the issue, we must check whether the IR function is empty before attempting to do any manipulation of its instructions.

This PR:

• Adds checks for whether IR Functions are empty() in each relevant RTSan pass routine
• Removes the utility function rtsanPreservedCFGAnalyses from the pass, whose result was unused and which would otherwise have complicated the fix

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: None (davidtrevelyan)

Changes

Addresses #169377.

Previously, the RealtimeSanitizer pass only handled attributed function definitions in IR, and attributed function declarations caused it to crash. To fix the issue, we must check whether the IR function is empty before attempting to do any manipulation of its instructions.

This PR:

• Adds checks for whether IR Functions are empty() in each relevant RTSan pass routine
• Removes the utility function rtsanPreservedCFGAnalyses from the pass, whose result was unused and which would otherwise have complicated the fix

---

Full diff: https://github.com/llvm/llvm-project/pull/169577.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Instrumentation/RealtimeSanitizer.cpp (+7-9)
• (added) llvm/test/Instrumentation/RealtimeSanitizer/rtsan_attrib_declare.ll (+12)

diff --git a/llvm/lib/Transforms/Instrumentation/RealtimeSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/RealtimeSanitizer.cpp
index 5ef6ffb58a7c1..adb0e518c6074 100644
--- a/llvm/lib/Transforms/Instrumentation/RealtimeSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/RealtimeSanitizer.cpp
@@ -61,23 +61,21 @@ static void insertCallAtAllFunctionExitPoints(Function &Fn,
       insertCallBeforeInstruction(Fn, I, InsertFnName, FunctionArgs);
 }
 
-static PreservedAnalyses rtsanPreservedCFGAnalyses() {
-  PreservedAnalyses PA;
-  PA.preserveSet<CFGAnalyses>();
-  return PA;
-}
+static void runSanitizeRealtime(Function &Fn) {
+  if (Fn.empty())
+    return;
 
-static PreservedAnalyses runSanitizeRealtime(Function &Fn) {
   insertCallAtFunctionEntryPoint(Fn, "__rtsan_realtime_enter", {});
   insertCallAtAllFunctionExitPoints(Fn, "__rtsan_realtime_exit", {});
-  return rtsanPreservedCFGAnalyses();
 }
 
-static PreservedAnalyses runSanitizeRealtimeBlocking(Function &Fn) {
+static void runSanitizeRealtimeBlocking(Function &Fn) {
+  if (Fn.empty())
+    return;
+
   IRBuilder<> Builder(&Fn.front().front());
   Value *Name = Builder.CreateGlobalString(demangle(Fn.getName()));
   insertCallAtFunctionEntryPoint(Fn, "__rtsan_notify_blocking_call", {Name});
-  return rtsanPreservedCFGAnalyses();
 }
 
 PreservedAnalyses RealtimeSanitizerPass::run(Module &M,
diff --git a/llvm/test/Instrumentation/RealtimeSanitizer/rtsan_attrib_declare.ll b/llvm/test/Instrumentation/RealtimeSanitizer/rtsan_attrib_declare.ll
new file mode 100644
index 0000000000000..a5336b9e9e491
--- /dev/null
+++ b/llvm/test/Instrumentation/RealtimeSanitizer/rtsan_attrib_declare.ll
@@ -0,0 +1,12 @@
+; RUN: opt < %s -passes='rtsan' -S | FileCheck %s
+
+declare void @declared_realtime_function() sanitize_realtime #0
+
+declare void @declared_blocking_function() sanitize_realtime_blocking #0
+
+; RealtimeSanitizer pass should ignore attributed functions that are just declarations
+; CHECK: declared_realtime_function
+; CHECK-EMPTY:
+; CHECK: declared_blocking_function
+; CHECK-EMPTY:
+

[cjappl]

Seems reasonable enough, just have some questions before I approve

[cjappl]

Is not returning these preserved analyses going to bite us elsewhere? I remember most of the sanitizer transform passes (or transform passes generally) returning these.

[cjappl]

Is there precedence in other sanitizer passes for doing this? (Curious how they solved this problem)

[luca3s]

Looks good! doesn't crash anymore and the rtsan tests i added to rustc also still pass.

[zwuis]

Addresses #169377.

You can use this format.