[cfe-dev] clang attributes to disable asan/tsan/msan

Kostya Serebryany kcc at google.com
Mon Feb 18 21:10:13 PST 2013

On Tue, Feb 19, 2013 at 3:55 AM, Chandler Carruth <chandlerc at google.com>wrote:

> On Mon, Feb 18, 2013 at 10:35 AM, Sean Silva <silvas at purdue.edu> wrote:
>> On Mon, Feb 18, 2013 at 8:31 AM, Kostya Serebryany <kcc at google.com>
>> wrote:
>> > Hi,
>> >
>> > Clang has two attributes to disable bug detection tools in a given
>> function:
>> >
>> > __attribute__((no_thread_safety_analysis)) disables clang's *static*
>> > thread-safety analysis.
>> > (
>> http://clang.llvm.org/docs/LanguageExtensions.html#thread-safety-annotation-checking
>> )
>> >
>> > __attribute__((no_address_safety_analysis)) disables AddressSanitizer
>> > (*dynamic* analysis)
>> >
>> http://clang.llvm.org/docs/LanguageExtensions.html#extensions-for-dynamic-analysis
>> >
>> > Now we need two more attributes to disable
>> > ThreadSanitizer (http://clang.llvm.org/docs/ThreadSanitizer.html)
>> > and MemorySanitizer (http://clang.llvm.org/docs/MemorySanitizer.html)
>> >
>> > For MemorySanitizer I propose __attribute__((no_uninitialized_checks))
>> > Objections? Better naming suggestion?
>> > Maybe __attribute__((no_memory_sanitizer))?
>> > (We deliberately named no-asan attribute "no_address_safety_analysis"
>> w/o
>> > mentioning asan
>> > in the name to make this attribute usable for other tools, e.g.
>> SAFECode.
>> > So,
>> > we may not want to tie the no-msan attribute to msan)
>> It seems to me like it is going to be simpler and more transparent to
>> have the attribute explicitly mention the sanitizer, e.g.`
>> __attribute__((no_sanitize("memory")))`; then the user knows exactly
>> what they are getting (since the name corresponds with the command
>> line option). If other tools want to use those attributes it's not
>> hard to look for them.
>> It also isn't entirely clear to me that the attribute would have
>> exactly the same semantics for the sanitizers and some other tool.
>> AFAIK the term "address safety" has no independent meaning and
>> basically means "the things that asan checks", so the term "address"
>> in `__attribute__((no_address_safety_analysis))` is already asan
>> specific in that regard, and it would be clearer to just say
>> `no_sanitize("memory")`.
>> If we really want the attributes to be tool-agnostic, then they should
>> describe what the function does that is naughty, e.g.
>> `__attribute__((reads_unintialized_memory_on_purpose))`, and let the
>> tool interpret that information and behave appropriately.
> This summarizes my feelings exactly.
> I think that even if we grow a set of attributes that describe the
> semantic oddity of a function (such as reading uninitialized memory, etc),
> we would still want an escape hatch to just turn off the sanitizer. And
> when we do that, we really do want to use the exact same terminology that
> we use in the flags.
> I don't think it matters whether its one attribute or N attributes as long
> as we get some naming consistency. I would propose (for simplicity of
> implementation mostly):
> __attribute__((no_sanitize_address))
> __attribute__((no_sanitize_memory))
> __attribute__((no_sanitize_thread))
> __attribute__((no_sanitize_undefined))

I like the simplicity (also because we will have to implement these
attributes in gcc too).

How about this?
__attribute__((no_sanitize_address)) is a synonym for
__attribute__((no_address_safety_analysis)), i.e. disables AddressSanitizer
(or maybe we should just leave no_address_safety_analysis?)

__attribute__((no_sanitize_memory)) disables MemorySanitizer checking, but
still keeps the instrumentation required to avoid false positives.

__attribute__((no_sanitize_thread)) disables ThreadSanitizer checking for
plain (non-atomic) loads/stores, but still keeps the instrumentation
required to avoid false positives.


> ...
> This pattern should be easy to remember and understand, and removes a lot
> of ambiguity of which attribute goes with which sanitizer. It also makes it
> very clear that these are attributes pertaining to the dynamic analysis
> toolset, not to any static analysis toolset.
> Of course, I think we should support the existing attributes for backwards
> compatibility, at least for several releases.
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