[PATCH] D126385: [msan] Implement -msan-pass-caller-to-runtime.

[Alexander Potapenko via Phabricator via llvm-commits]

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In D126385#3542914 <https://reviews.llvm.org/D126385#3542914>, @vitalybuka wrote:

> Do you have estimate of how often this happend? How many different instrumented functions which can be called from uninstrumented code?

There are ~200 noinstr annotations in the Linux kernel. Some are used in macros (e.g. there are several dozens of interrupt descriptor table entries that are implemented as noinstr functions).
It's hard to tell how many instrumented functions end up being called with consequences, but certainly annotating them manually is not an option.

We could probably optimize by not passing __builtin_return_address() to __msan_get_context_state() if the instrumented function doesn't take any arguments. Not sure it is worth the hassle (we'll need a separate version of __msan_get_context_state())



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Comment at: llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp:1274
+            Intrinsic::getDeclaration(F.getParent(), Intrinsic::returnaddress),
+            IRB.getInt32(0));
+        ContextState = IRB.CreateCall(MS.MsanGetContextStateFn, RetAddr);
----------------
vitalybuka wrote:
> Can you avoid ClPassCallerToRuntime and always pass the argument? I guess function will just not use it.
> 
This would cost us a register spill, sounds like a regression for *BSD systems that don't need the argument.


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