[llvm-dev] (Thin)LTO llvm build

[Teresa Johnson via llvm-dev]

On Mon, Oct 3, 2016 at 3:53 PM, Xinliang David Li <xinliangli at gmail.com>
wrote:

> What is the linker command line buidling liblldb.so? is libgcc.a passed in?
>

There is no difference in the linker command for liblldb.so or bin/lldb
between the ld.bfd and ld.gold cases, and neither links libgcc.a that I can
see.

The difference appears to be that the __morestack symbol is weak in the
ld.gold liblldb.so case (and simply doesn't appear in the resulting
bin/lldb presumably because libgcc.a is not linked):

$ nm lib/liblldb.so.3.9.1 | grep morestack
                 w __morestack

whereas it is an undef in the ld.bfd case:

$ nm lib/liblldb.so | grep morestack
                 U __morestack

resulting in the failure linking bin/lldb in that case.


> David
>
> On Mon, Oct 3, 2016 at 3:52 PM, Xinliang David Li <xinliangli at gmail.com>
> wrote:
>
>> In  uint64_t
>> RTDyldMemoryManager::getSymbolAddressInProcess(const std::string &Name)
>>  {
>>
>> there is reference to morestack:
>>
>>
>>
>> #if defined(__i386__) || defined(__x86_64__)
>>   // __morestack lives in libgcc, a static library.
>>   if (&__morestack && Name == "__morestack")
>>     return (uint64_t)&__morestack;
>> #endif
>> #endif // __linux__ && __GLIBC__
>>
>>
>> On Mon, Oct 3, 2016 at 3:32 PM, Teresa Johnson <tejohnson at google.com>
>> wrote:
>>
>>>
>>>
>>> On Mon, Oct 3, 2016 at 2:59 PM, Xinliang David Li <xinliangli at gmail.com>
>>> wrote:
>>>
>>>> Is -fsplit-stack option used anywhere? My wild guess is that with
>>>> ld.bfd, the thinLTO link for the DSO does not bring in morestack.o from
>>>> libgcc.a, but the hidden symbol is defined in lldb binary.
>>>>
>>>
>>> AFAICT, no - I had done "ninja -v" so I have all of the intermediate
>>> build commands, and it doesn't show up in that.
>>>
>>> I'll have to do some more digging to figure out why it is referenced
>>> from liblldb.so in the ld.bfd case and not when using ld.gold
>>>
>>> Teresa
>>>
>>> David
>>>>
>>>> On Mon, Oct 3, 2016 at 1:54 PM, Teresa Johnson via llvm-dev <
>>>> llvm-dev at lists.llvm.org> wrote:
>>>>
>>>>> Aha - finally reproduced! The difference is using ld.bfd not ld.gold.
>>>>> With that I get the same failure (using 3.9 to build 3.9 sources):
>>>>>
>>>>> /usr/local/google/home/tejohnson/binutils_build/install/bin/ld:
>>>>> bin/lldb-3.9.1: hidden symbol `__morestack' in
>>>>> /usr/lib/gcc/x86_64-linux-gnu/4.8/libgcc.a(morestack.o) is referenced
>>>>> by DSO
>>>>> /usr/local/google/home/tejohnson/binutils_build/install/bin/ld: final
>>>>> link failed: Bad value
>>>>> clang-3.9: error: linker command failed with exit code 1 (use -v to
>>>>> see invocation)
>>>>> ninja: build stopped: subcommand failed.
>>>>>
>>>>> I am not sure what the official support story is for LLVMgold.so and
>>>>> ld.bfd. As mentioned earlier, the LLVM site indicates it should use the
>>>>> gold linker. Can you use that while I try to figure out whether this is
>>>>> something that should be supported/working?
>>>>>
>>>>> Thanks,
>>>>> Teresa
>>>>>
>>>>> On Mon, Oct 3, 2016 at 9:56 AM, Carsten Mattner <
>>>>> carstenmattner at gmail.com> wrote:
>>>>>
>>>>>> On Mon, Oct 3, 2016 at 3:50 PM, Teresa Johnson <tejohnson at google.com>
>>>>>> wrote:
>>>>>> >
>>>>>> > On Sun, Oct 2, 2016 at 4:02 AM, Carsten Mattner <
>>>>>> carstenmattner at gmail.com> wrote:
>>>>>> >>
>>>>>> >> On Sun, Oct 2, 2016 at 6:41 AM, Teresa Johnson <
>>>>>> tejohnson at google.com> wrote:
>>>>>> > >
>>>>>> > > > I use trunk, but it depends on how close to the bleeding edge
>>>>>> you
>>>>>> > > > are comfortable with. But like I said, I also tried
>>>>>> bootstrapping
>>>>>> > > > with 3.9 (both trunk as well as 3.9 sources) and couldn't
>>>>>> reproduce.
>>>>>> >>
>>>>>> >> Hmm, so you're saying neither fails for you, right?
>>>>>> >
>>>>>> > Yes
>>>>>>
>>>>>> Okay. Do you mind focusing on the 3.9 branch? It's less of a moving
>>>>>> target
>>>>>> and lends itself more to figuring out what's failing for me.
>>>>>>
>>>>>> As soon as I get around to it, I'll send you my full configure and
>>>>>> build
>>>>>> steps as a shell script. Need to streamline it.
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>>>>> 408-460-2413
>>>>>
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> llvm-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>
>>>>>
>>>>
>>>
>>>
>>> --
>>> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>>> 408-460-2413
>>>
>>
>>
>


-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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