[llvm-dev] (Thin)LTO llvm build
Xinliang David Li via llvm-dev
llvm-dev at lists.llvm.org
Mon Oct 3 17:24:44 PDT 2016
Small repro:
__attribute__((weak)) int hello_world();
int test() {
if (hello_world)
return hello_world();
return 0;
}
$ clang -fuse-ld=gold -flto=thin -O2 -shared -fPIC -o libmore.so more.c
$ objdump -t libmore.so |grep hello
0000000000000000 w *UND* 0000000000000000 hello_world
$ clang -fuse-ld=bfd -flto=thin -O2 -shared -fPIC -o libmore.so more.c
$ objdump -t libmore.so |grep hello
0000000000000000 *UND* 0000000000000000 hello_world
On Mon, Oct 3, 2016 at 4:40 PM, Teresa Johnson <tejohnson at google.com> wrote:
>
>
> 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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