-static-libgcc vs. -Wl,-Bstatic -lgcc

[Volker Simonis]

On 6/13/15, Magnus Ihse Bursie <magnus.ihse.bursie at oracle.com> wrote:
> Volker,
>
> Thanks for your analysis. The static/dynamic stdc++ linking is messy, quite
> possibly even broken in the current implemenation. I have opened a bug for
> that but can't find it now. The current implemenation in libraries.m4 will
> replace LDCXX (that is, g++) with LD (that is, gcc) which caused some
> internal Oracle code to break. Apparently, it works without breaking the
> build for the open part, but that still looks weird. If we explicitly
> request to use a toolchain which links with g++, then we shouldn't replace
> it with gcc just because we're doing static linking.
>
> Also, I had not heard about -static-libgcc before (and apparently hadn't
> Fredrik who wrote the original piece of --with-stdc++lib handling), but it
> seems like that should be used, for all the platform, yes.
>
> Do we even have to use  -Wl,-Bstatic -lstdc++ when -static-libgcc is
> present?
>

I think we don't need -lgcc if -static-libgcc is present.

> If it turns out that this is something we will want to fix in jdk9/dev as
> well, we typically do either of:
> A) fixing it directly in jdk9/dev as a separate bug, and then pull it into
> build-infra after a while when it's propagated into a build, or
> B) fix it in build-infra, and then pick the relevant parts and put them as a
> separate bug into jdk9/dev, possibly requiring some merge changes when they
> get back after a while.
>
> B is preferable if it's required urgently in build-infra, or it might need
> several iterations to get it right. Otherwise A is simpler.
>

I think the change is not urgent but it should be done right:)

I think the following questions must be addressed:

- do we really need to statically link libgcc (we at SAP and others
like RedHat are not doing this since quite some time without problems.
- do we really need to statically link libstdc++ (there have been
already some good mail threads regarding this topic)
- we should ensure that all C++ libraries in the JDK are linked in the
same way with regard to libgcc and libstdc++

These discussions should be probably held on the hotspot-dev list.

Regards,
Volker

> /Magnus
>
>> 12 jun 2015 kl. 19:50 skrev Volker Simonis <volker.simonis at gmail.com>:
>>
>> Hi,
>>
>> while porting the new HS build to linux/ppc64 I saw that we are now
>> setting
>> some link options unconditionally trough the $(LIBCXX) variable from the
>> top-level spec.gmk (whihc is good :). With the default configuration,
>> this
>> variable will contain the value "-Wl,-Bstatic -lstdc++ -lgcc" but this
>> can
>> be changed by setting --with-stdc++lib=dynamic. Nevertheless, we still
>> set
>> "-static-libgcc" unconditionally in Common.gmk
>>
>> Now there's one think I don't understand (and which isn't related to
>> ppc64). I thought "-static-libgcc" and "-Wl,-Bstatic -lgcc" should be
>> equivalent options, but apparently they aren’t. For the new build we use
>> "-Wl,-Bstatic -lstdc++ -lgcc" and additionally set "-static-libgcc". I
>> thought it should be possible to remove the "-static-libgcc" setting from
>> the new HS build system (because the question static/dynamic linking of
>> libstdc++ should be decided at configure time with the --with-stdc++lib
>> option. But this will produce a different results.
>>
>> Summing it up:
>>
>> old build:
>> -static-libgcc -Wl,-Bstatic -lstdc++       -Wl,-Bdynamic -lm -ldl
>> -lpthread
>>
>> is the same as new build:
>> -static-libgcc -Wl,-Bstatic -lstdc++ -lgcc -Wl,-Bdynamic -lm -ldl
>> -lpthread
>>
>> but not the same as the new build without "-static-libgcc":
>>               -Wl,-Bstatic -lstdc++ -lgcc -Wl,-Bdynamic -lm -ldl
>> -lpthread
>> which dynamically links ibgcc_s.so.1 (at least on x86_64)
>>
>> It turns out (if you run gcc with '-v') that with "-static-libgcc" the
>> command line expands to:
>> -lgcc -lgcc_eh -lc -lgcc -lgcc_eh
>> which will all be statically linked.
>>
>> while without "-static-libgcc" it expands to:
>> -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s
>> --no-as-needed
>> and dynamically links libgcc_s.so.1 (at least on x86_64 but not on
>> ppc64).
>>
>> The problem is that "libgcc_s.so.1" is only available as shared library
>> so
>> we can't statically link it even if we want.
>>
>> So should we move "-static-libgcc" to libraries.m4 to the place where we
>> detect whether to use  --with-stdc++lib=static/dynamic because we
>> apparently can't live without it if we still want to link libgcc
>> statically?
>>
>> Regards,
>> Volker
>