[LLVMdev] [RFC] Parsing runtime flags in sanitizers (ASan/LSan/UBSan)

[Alexey Samsonov]

On Mon, Dec 8, 2014 at 2:00 AM, Alexander Potapenko <glider at google.com>
wrote:

> Hope you're assuming there's always a single copy of common_flags in
> the process.
>

Yes.


> This isn't the case for e.g. ASan+UBSan on Mac, but that's a broken setup.
>

Yes. I assume, we want to have dynamic UBSan runtime on Mac, don't we?


>
> What if we let the tools protect specific flags (by adding a bool to
> each flag) once they set their values (when setting the default
> values, parsing xSAN_OPTIONS, etc)
> Generally, I think we need to protect each flag when anyone's trying
> to read it (so we'll need getters and setters for the flags), unless
> the code opts out of protecting a particular flag (e.g. if we want to
> allow it to be changed dynamically).
> This way we can prevent the flags from being overridden with conflicting
> values.
>

What is the purpose of making the flag values immutable? If you want to
protect against the case
where we accidentally reset the flag value, you can just make
common_flags() accessor return a const
reference. Then you'd only be able to modify the flag values explicitly via
ParseCommonFlagsFromString()
and similar functions. This would certainly be a positive change.

IMO it would be *very* hard to distinguish between cases when we
override flags on purpose (e.g. override defaults from env var) and when we
override them accidentally during
multiple tool initializatier calls (the case which I describe).


>
> Irrespective of whether we protect the flags or not, I think we need
> to distinguish between the flags that can be set once and flags that
> may change their values (e.g. on Android).
>

Anyway, this suggestion is kind of orthogonal to mine. I was asking if
you're ok with having "main" tool (ASan)
steal responsibility of initializing runtime flags from "plug-in" tools
(LSan, UBSan).



>
> On Sat, Dec 6, 2014 at 2:51 AM, Alexey Samsonov <vonosmas at gmail.com>
> wrote:
> > Hi all,
> >
> > TL;DR
> > 1) We should change the way we parse common runtime flags in sanitizers.
> > 2) We should make ASan aware of the tools it can be combined with (LSan
> and
> > UBSan).
> > 3) We may have to restrict the tools UBSan can be combined with
> (currently
> > to ASan) (see [1])
> >
> > Currently we have two kinds of sanitizer runtime flags: tool-specific
> flags
> > and "common flags", defined in sanitizer_common library and shared across
> > all the sanitizers. Many of these common flags are used early during tool
> > initialization (for example, we use "suppressions" flag to create
> > SuppressionContext singleton object). That's the reason why we parse both
> > tool-specific flags and common flags as early as possible at program
> > startup, before running the rest of initialization code. It all works
> fine
> > until we have a single sanitizer - e.g. for TSan or MSan.
> >
> > The situation gets crazy when we combine multiple sanitizers in a single
> > process, for instance use ASan+LSan+UBSan (the default use case in some
> > setups). Each tool has its own defaults for common flag values, and each
> of
> > ASAN_OPTIONS, LSAN_OPTIONS and UBSAN_OPTIONS can define both
> tool-specific
> > and common flags. These environment variables are parsed at different
> time,
> > sometimes in undefined order. We can easily end up in situation where
> ASan
> > initializes some parts of sanitizer_common assuming certain values of
> common
> > runtime flags, but then these flags are overwritten by LSAN_OPTIONS. All
> > this is very complicated and fragile.
> >
> > I propose to implement the following:
> >
> > ASan flag parsing:
> > 1) Detect all sanitizers ASan is combined with (We know that we have
> LSan if
> > "CAN_SANITIZE_LEAKS" is true. We can detect if we have UBSan in the
> process
> > somehow.)
> > 2) Setup defaults for ASan-specific flags and override them from
> > ASAN_OPTIONS.
> > 3) Setup defaults for common flags and override them from all of
> > ASAN_OPTIONS, LSAN_OPTIONS and UBSAN_OPTIONS (if corresponding sanitizers
> > are enabled for the process).
> > 4) Proceed with initialization, and call LSan/UBSan initializers when
> > appropriate.
> >
> > LSan/UBSan flag parsing:
> > 1) Learn if LSan/UBSan are combined with ASan (the "main" tool) or run as
> > standalone tool. This is already done for LSan and can be done for UBSan
> by
> > slightly modifying the way we structure runtimes.
> > 2) Setup defaults for tool-specific flags and override them from
> > LSAN/UBSAN_OPTIONS.
> > 3) If the tools run in standalone mode, setup the defaults for common
> flags
> > and override them from LSAN/UBSAN_OPTIONS. If the tools are combined with
> > "main" tool, do nothing.
> > 4) Proceed with initialization.
> >
> > [1] Conjecture:
> > 1) We will have to add the hook to initialize UBSan that we would invoke
> > from ASan (much like we do for LSan). It means that we would have to
> > restrict the set of sanitizers that can be combined with UBSan (allowing
> it
> > for another sanitizers would be very easy, but manual process). The
> > alternative would be to make UBSan setup no-op except for parsing the
> flags,
> > so that UBSan initializer could be safely called before main tool
> > initializer.
> >
> > Bonus:
> > 1) We will be able to significantly improve runtime flag parsing
> diagnostic.
> > For instance, we would be able to report conflicting flag definitions
> (e.g.
> > when one provides ASAN_OPTIONS=symbolize=0 LSAN_OPTIONS=symbolize=1).
> >
> > Comments/objections?
> >
> > --
> > Alexey Samsonov
> > vonosmas at gmail.com
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >
>
>
>
> --
> Alexander Potapenko
> Software Engineer
> Google Moscow
>



-- 
Alexey Samsonov
vonosmas at gmail.com
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