llvm dev - Mar 2019 - Trying to create a pure LLVM toolchain on musl based distribution

Le 25/03/2019 à 14:41, Peter Smith a écrit :
> Hello David,
> 
> I don't know much about the specifics of Musl, so I'm responding
generally.
> 
> As I understand it, clang expects to find the compiler-rt libraries
> relative to the resource directory, which you can find out the
> location of with clang --print-resource-dir . By default it is
> lib/clang/9.0.0 assuming you are building from master. I think that
> -DCMAKE_INSTALL_PREFIX=/usr has broken that assumption. I think that
> you would either need to take out the CMAKE_INSTALL_PREFIX or change
> the location of the resource directory, which I think that you can
> alter at build time.
> 
You're right, I've just checked both packages in Alpine and Arch and 
they indeed move the /usr/lib/linux directory under the clang's one. 
I've fixed that it worked, now I still have to find the solution 
regarding crtbeginS.so and crtendS.so.

Thanks :)
> I don't think that there is a way of preventing clang adding
> crtbeginS.o and crtendS.o without --nostdlib or --nostartfiles but
> using these options will also not add the other crt*.o files that you
> may be expecting.
> 
> There is a line in lib/Driver/Toolchains/Gnu.cpp which the Linux driver
uses:
> const bool HasCRTBeginEndFiles >       
ToolChain.getTriple().hasEnvironment() ||
>        (ToolChain.getTriple().getVendor() !=
llvm::Triple::MipsTechnologies);
> It looks like Musl may need to be included there?
I'll have a look, I don't know much the lowest part of the toolchain 
build process so I don't understand very much what's going on there. 
Hopefully someone that has better low-level knowledges and use musl will 
be able to guide me for this.

What can I tell is that musl provide those files:

usr/lib/Scrt1.o
usr/lib/crt1.o
usr/lib/crti.o
usr/lib/crtn.o
usr/lib/ld-musl-x86_64.so.1

Regards,

-- 
David

On Mon, Mar 25, 2019 at 7:05 AM David Demelier via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Le 25/03/2019 à 14:41, Peter Smith a écrit :
> > Hello David,
> >
> > I don't know much about the specifics of Musl, so I'm
responding
> generally.
> >
> > As I understand it, clang expects to find the compiler-rt libraries
> > relative to the resource directory, which you can find out the
> > location of with clang --print-resource-dir . By default it is
> > lib/clang/9.0.0 assuming you are building from master. I think that
> > -DCMAKE_INSTALL_PREFIX=/usr has broken that assumption. I think that
> > you would either need to take out the CMAKE_INSTALL_PREFIX or change
> > the location of the resource directory, which I think that you can
> > alter at build time.
> >
>
> You're right, I've just checked both packages in Alpine and Arch
and
> they indeed move the /usr/lib/linux directory under the clang's one.
> I've fixed that it worked, now I still have to find the solution
> regarding crtbeginS.so and crtendS.so.
>
https://reviews.llvm.org/D28791 should address this. We're still discussing
some related aspects on https://reviews.llvm.org/D59264, but I'm hoping to
reach a conclusion and land these changes this week.

> Thanks :)
>
> > I don't think that there is a way of preventing clang adding
> > crtbeginS.o and crtendS.o without --nostdlib or --nostartfiles but
> > using these options will also not add the other crt*.o files that you
> > may be expecting.
> >
> > There is a line in lib/Driver/Toolchains/Gnu.cpp which the Linux
driver
> uses:
> > const bool HasCRTBeginEndFiles > >       
ToolChain.getTriple().hasEnvironment() ||
> >        (ToolChain.getTriple().getVendor() !>
llvm::Triple::MipsTechnologies);
> > It looks like Musl may need to be included there?
>
> I'll have a look, I don't know much the lowest part of the
toolchain
> build process so I don't understand very much what's going on
there.
> Hopefully someone that has better low-level knowledges and use musl will
> be able to guide me for this.
>
> What can I tell is that musl provide those files:
>
> usr/lib/Scrt1.o
> usr/lib/crt1.o
> usr/lib/crti.o
> usr/lib/crtn.o
> usr/lib/ld-musl-x86_64.so.1
>
> Regards,
>
> --
> David
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20190325/6d0ff34f/attachment.html>

On Mon, Mar 25, 2019 at 07:54:54AM -0700, Petr Hosek
wrote:
> On Mon, Mar 25, 2019 at 7:05 AM David Demelier via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> 
> > Le 25/03/2019 à 14:41, Peter Smith a écrit :
> > > Hello David,
> > >
> > > I don't know much about the specifics of Musl, so I'm
responding
> > generally.
> > >
> > > As I understand it, clang expects to find the compiler-rt
libraries
> > > relative to the resource directory, which you can find out the
> > > location of with clang --print-resource-dir . By default it is
> > > lib/clang/9.0.0 assuming you are building from master. I think
that
> > > -DCMAKE_INSTALL_PREFIX=/usr has broken that assumption. I think
that
> > > you would either need to take out the CMAKE_INSTALL_PREFIX or
change
> > > the location of the resource directory, which I think that you
can
> > > alter at build time.
> > >
> >
> > You're right, I've just checked both packages in Alpine and
Arch and
> > they indeed move the /usr/lib/linux directory under the clang's
one.
> > I've fixed that it worked, now I still have to find the solution
> > regarding crtbeginS.so and crtendS.so.
> >
> 
> https://reviews.llvm.org/D28791 should address this. We're still
discussing
> some related aspects on https://reviews.llvm.org/D59264, but I'm hoping
to
> reach a conclusion and land these changes this week.
>
Nice, thanks. I've applied D28791 in compiler-rt 8.0.0 without problems.
Howerver D59264 does not apply correctly on clang 8.0.0. Will there be an
intermediate version before 9.0.0? Otherwise I'll try to update the patch
for 8.0.0.
 
> 
> > Thanks :)
> >
> > > I don't think that there is a way of preventing clang adding
> > > crtbeginS.o and crtendS.o without --nostdlib or --nostartfiles
but
> > > using these options will also not add the other crt*.o files that
you
> > > may be expecting.
> > >
> > > There is a line in lib/Driver/Toolchains/Gnu.cpp which the Linux
driver
> > uses:
> > > const bool HasCRTBeginEndFiles > > >       
ToolChain.getTriple().hasEnvironment() ||
> > >        (ToolChain.getTriple().getVendor() !> >
llvm::Triple::MipsTechnologies);
> > > It looks like Musl may need to be included there?
> >
> > I'll have a look, I don't know much the lowest part of the
toolchain
> > build process so I don't understand very much what's going on
there.
> > Hopefully someone that has better low-level knowledges and use musl
will
> > be able to guide me for this.
> >
> > What can I tell is that musl provide those files:
> >
> > usr/lib/Scrt1.o
> > usr/lib/crt1.o
> > usr/lib/crti.o
> > usr/lib/crtn.o
> > usr/lib/ld-musl-x86_64.so.1
> >
> > Regards,
> >
> > --
> > David
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
Regards,

-- 
David Demelier