[patch/asan] Use lvm.global_ctors instead of symbol name matching to find constructors

[Reid Kleckner]

No, it's more basic.

If I understand the current ASan init-order instrumentation, it only
poisons globals of other TUs during _GLOBAL__*.  Initializers of static
data members of class templates get their own llvm.global_ctors entry, so
other globals are not poisoned, and we get false negatives.


On Wed, May 7, 2014 at 12:46 AM, Kostya Serebryany <kcc at google.com> wrote:

> This is https://code.google.com/p/address-sanitizer/issues/detail?id=215,
> isn't it?
>
>
> On Wed, May 7, 2014 at 4:07 AM, Reid Kleckner <rnk at google.com> wrote:
>
>> This is a good idea, because it will catch more bugs.  Consider this C++:
>>
>> int foo();
>> template <int N> struct X { static int x; };
>> template <int N> int X<N>::x = foo();
>> int main() { return X<0>::x + X<2>::x + X<3>::x + X<4>::x; }
>>
>> This will put 4 entries into llvm.global_ctors, none of which are called
>> _GLOBAL__*.  We should probably have an ASan integration test in
>> compiler-rt for this, when foo accesses some global in a different TU.
>>
>> On the other hand, all this poisoning and unpoisoning may be expensive.
>>  We could batch up all the initializers of equal priority and merge them
>> into one initializer bracketed by calls to poison and unpoison.
>>
>>
>> On Tue, May 6, 2014 at 4:55 PM, Nico Weber <thakis at chromium.org> wrote:
>>
>>> Hi,
>>>
>>> here's how the global_ctors version would look. I haven't tested this
>>> much (it's different in that it could now instrument multiple
>>> constructors per module).
>>>
>>> Feel free to play with this, and then land this with tweaks, land it
>>> as-is, or don't land it, up to you :-)
>>>
>>> Nico
>>>
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>>>
>>
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