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

[Alexander Potapenko]

Hope you're assuming there's always a single copy of common_flags in
the process.
This isn't the case for e.g. ASan+UBSan on Mac, but that's a broken setup.

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.

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).

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
>
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>



-- 
Alexander Potapenko
Software Engineer
Google Moscow