[libcxx] r243574 - Recommit r243503 "[libcxx] Cleanup CMake configuration and integrate with LLVM"

[Eric Fiselier]

> Eric, what part of your change caused this behavior change? Probably, after you've started to execute LLVM CMake modules,
> you've modified link flags used to build shared objects, and now they are required to have no unresolved symbols?

This is exactly what is happening. HandleLLVMOptions.cmake adds
"-Wl,-z,defs" on linux when LLVM_USE_SANITIZER is not specified.
We also pick up -ffunction-sections and -fdata-sections. What effect
do those have on building with sanitizers?


One of the main reasons for this patch was to make it easier for
libc++ to support sanitizer configurations.
I would like the libc++ build to support each sanitizer configuration.
Currently it seems like compiler-rt is better at
building libc++ with sanitizers than libc++ is.

Would anybody be willing to help with:
A) Figuring out the proper flags for building and linking libc++ with
each sanitizer.
B) Moving some of the compiler-rt CMake logic for building libc++ into
libc++ if applicable.

/Eric

On Wed, Jul 29, 2015 at 8:54 PM, Alexey Samsonov <vonosmas at gmail.com> wrote:
> I've submitted r243599 that slightly improves things: now libcxx can be
> configured with "Clang+TSan", but the build fails with a bunch of
>   "undefined reference to `__tsan_read8'"
> errors when we are trying to link libc++.so.
>
> Generally, we *don't* link in TSan runtime into shared objects - it should
> only be linked into the executable, and __tsan_* symbols should be
> left unresolved. Eric, what part of your change caused this behavior change?
> Probably, after you've started to execute LLVM CMake modules,
> you've modified link flags used to build shared objects, and now they are
> required to have no unresolved symbols?
>
> On Wed, Jul 29, 2015 at 5:21 PM, Alexey Samsonov <vonosmas at gmail.com> wrote:
>>
>> I think I've found the "problem", causing CMake identification of Clang
>> version. I will submit it shortly.
>>
>> On Wed, Jul 29, 2015 at 4:50 PM, Kostya Serebryany <kcc at google.com> wrote:
>>>
>>> Thanks, check-msan works for me again.
>>>
>>>
>>>
>>> On Wed, Jul 29, 2015 at 4:47 PM, Eric Fiselier <eric at efcs.ca> wrote:
>>>>
>>>> Reverted as r243593.
>>
>>
>>
>>
>> --
>> Alexey Samsonov
>> vonosmas at gmail.com
>
>
>
>
> --
> Alexey Samsonov
> vonosmas at gmail.com