[LLVMdev] Intercepting dlinfo in memory sanitizer

[Keno Fischer]

Hi everyone,

I ran into a false positive with memory sanitizer due to it not
intercepting dlinfo. I tried to get started on writing such an interceptor,
but dlinfo seems like an extraordinarily difficult function to intercept.
The three considerations that I would like somebody to look at are:

1) How do we get the enum values to decide what kind of pointer dlinfo is
getting. Ideally we'd include dlfcn.h, but the interceptor file doesn't
generally include system headers. What's the right thing to do here?
2) The structures pointed to contain linked lists, etc. of dynamic linker
state. In order to avoid spurious failures, it seems like we should iterate
the linked lists and unpoison all of them, but that seems expensive. Do you
see a better solution?
3) The return values include pointers into the object files. It seems
perfectly reasonable for a user to want to read these object files based on
information from dlinfo. That probably means we should unpoison them as
well? Do we need to do something here or are these already unpoisoned by
some other mechanism (e.g. because msan realizes they are part of a loaded
object file or unposions them on load - does this happen?).

Thanks,
Keno
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