[LLVMdev] Special case list files; a bug and a slowness issue

[Alexey Samsonov]

Hi Peter!

On Sat, Jul 13, 2013 at 4:38 AM, Peter Collingbourne <peter at pcc.me.uk>wrote:

> Hi,
>
> I need to be able to use a special case list file containing thousands
> of entries (namely, a list of libc symbols, to be used when using
> DFSan with an uninstrumented libc).  Initially I built the symbol
> list like this:
>
> fun:sym1=uninstrumented
> fun:sym2=uninstrumented
> fun:sym3=uninstrumented
> ...
> fun:sym6000=uninstrumented
>
> What I found was that, despite various bits of documentation [1,2],
> the symbol names are matched as substrings, the root cause being that
> the regular expressions built by the SpecialCaseList class do not
> contain anchors.  The attached unit test demonstrates the problem.
> If I modify my symbol list to contain anchors:
>
> fun:^sym1$=uninstrumented
> fun:^sym2$=uninstrumented
> fun:^sym3$=uninstrumented
> ...
> fun:^sym6000$=uninstrumented
>
> the behaviour is as expected, but compiler run time is slow (on the
> order of seconds), presumably because our regex library doesn't cope
> with anchors very efficiently.
>
> I intend to resolve the substring bug and the slow run time issue
> by using a StringSet for symbol patterns which do not contain regex
> metacharacters.  There would still be a regex for any other patterns,
> which would have anchors added automatically.
>

I think that it's fine to add anchors automatically to implement the
behavior
described in the docs (I've LGTMed that patch). Do you want to avoid adding
anchors
for dfsan SpecialCaseList?


>
> Thoughts?
>
> Thanks,
> --
> Peter
>
> [1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizer
> [2] https://code.google.com/p/thread-sanitizer/wiki/Flags
>



-- 
Alexey Samsonov, MSK
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