[LLVMdev] RFC: How can AddressSanitizer, ThreadSanitizer, and similar runtime libraries leverage shared library code?

[Chandler Carruth]

On Thu, Jun 21, 2012 at 2:39 AM, Alexey Samsonov <samsonov at google.com>wrote:

>
>
> On Thu, Jun 21, 2012 at 1:34 PM, Dmitry Vyukov <dvyukov at google.com> wrote:
>
>> On Thu, Jun 21, 2012 at 1:30 PM, Chandler Carruth <chandlerc at google.com>wrote:
>>
>>>  Can we alter the build system so that when building a run-time library
>>>>>>> it modifies all .cpp files like this:
>>>>>>>    namespace FOO {
>>>>>>>    <file body>
>>>>>>>    }
>>>>>>> This will give us essentially the same thing, but w/o system
>>>>>>> dependent object file hackery.
>>>>>>> Maybe we can add a Clang flag to add such a namespace for us?
>>>>>>>
>>>>>>
>>>>>> I think this is essentially what Dmitry was talking about w/ past
>>>>>> STLport experience. It has lots of limitations:
>>>>>>
>>>>>
>>>>> Patching object files still sounds much scarier and harder to port.
>>>>> I'd prefer to find a solution that involves only source files and
>>>>> maybe clang.
>>>>> Pondering...
>>>>>
>>>>>
>>>>>> - You can't use the normal system standard library
>>>>>>
>>>>> - You have to build the standard library from source
>>>>>> - You can't wrap certain parts of it (operator new, delete, a few
>>>>>> other things)
>>>>>> - You can't re-use any C libraries (zlib for example)
>>>>>>
>>>>>
>>>>
>>>> Perhaps you are solving a broader problem. But as for asan/tsan, we
>>>> currently need only symbolizer, it's separable from everything else, and
>>>> can be made to not use STL.
>>>>
>>>
>>> If you want to share LLVM code for the object and dwarf reading, I do
>>> not believe this to be true at all.
>>>
>>
>> I've already removed code for the object reading for exactly that reason,
>> so now it's just dwarf parsing :) There are some CTL containers involved,
>> but I think they can be replaced.
>>
>
> Agree here. I hope to modify/extend this code soon anyway.
>

Folks, this is not the path to sharing code. This is the path to forking
code.

Let's go back to the very premise: I think it is highly desirable to be
capable of building runtimes such as ASan and TSan and *share* code rather
than forking it.

I have reasons: I have seen the creation of at least three separate ELF
and/or DWARF parsing libraries thus far. I have seen a long series of bugs
found and fixed in them over the course of years, often the same bug, often
with great expense in debugging to understand why. I don't want us to keep
paying this cost. I don't think these pieces of code are likely to be alone
in this.


Now, perhaps I am wrong, and it is not worth it. Thus far, I don't hear any
convincing arguments to that effect, but I'm very willing to believe I'm
wrong as I don't work on one of these runtimes, and so don't have a direct
appreciation for all of the costs involved.

But let's be extremely clear on what you are suggesting: you are
specifically doing away with the very idea of sharing code with the rest of
the LLVM project, and instead deciding to fork and write custom code in the
runtime for all functionality.
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