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[rtsan] Handle attributed IR function declarations #169577

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[rtsan] Handle attributed IR function declarations #169577

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16 changes: 7 additions & 9 deletions llvm/lib/Transforms/Instrumentation/RealtimeSanitizer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
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@cjappl cjappl Nov 26, 2025

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

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@davidtrevelyan davidtrevelyan Nov 29, 2025

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Thanks for the good idea. I hadn't looked before drafting this PR, but it appears like ASan solves it a similar way at one level higher - at the top level of the pass's run method:

llvm-project/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

Line 1318 in f5742c4

if (F.empty())

ThreadSanitizer has a bool check for whether it should sanitizeFunction, which returns false if there are no calls in it. MemorySanitizer does the same thing as AddressSanitizer with a continue at the top level if the function is .empty().

If you prefer the ASan/MSan semantics I'm very happy to switch to it 👍


static PreservedAnalyses runSanitizeRealtime(Function &Fn) {
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@cjappl cjappl Nov 26, 2025

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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.

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@davidtrevelyan davidtrevelyan Nov 29, 2025 •
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Perhaps! But the issue is we're already not returning these preserved analyses - they're sadly discarded at the moment. I would advocate for this NFC because it makes the current behaviour explicit - even if it's not correct. I bundled this change in with this PR because it made the implementation of the checking a bit easier, but I'd be happy to submit this in a separate preparatory PR first - if that's easier to follow - just let me know.

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,
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12 changes: 12 additions & 0 deletions llvm/test/Instrumentation/RealtimeSanitizer/rtsan_attrib_declare.ll
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Original file line number Diff line number Diff line change
@@ -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: