Re: Failed to build glibc with clang for aarch64

[Zhu Simon <prog13579@gmail.com>]

Hello Adhemerval,

Thanks for you kind help, it can work on my system (Ubuntu 20.04 and llvm
13.0.0) now with your latest commit, thanks!

Best Regards,
Simon

Adhemerval Zanella <adhemerval.zanella@linaro.org> 于2022年4月29日周五 22:24写道：

>
>
> On 29/04/2022 01:23, T P via Libc-help wrote:
> > Hello Adhemerval and all,
> >
> > I checkout your branch azanella/clang and use the below commit (
> >
> https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=c8b0172687a7b862fdd5229d95c513b9d0b64dcb
> ),
> > I build glibc with clang for x86 successfully, that's great. Then I try
> to
> > build it for aarch64 using the below config:
> > ../configure CC="clang --target=aarch64" CXX="clang++ --target=aarch64"
> > --target=aarch64 --host=aarch64-linux-gnu --disable-werror --prefix=/usr
>
> I have updated my branch with a master rebase, so it should not be in sync
> the my current work (I was not sure how old sourceware one was).
>
> On the system I use (ubuntu 22.04) it requires you install the default
> aarc64
> sysroot, done by install aarch64-linux-gnu-gcc pacakge (iy might vary
> depending
> of the distribution).
>
> I also noted that triplet used for clang, 'aarch64', is not suffice.  You
> will
> need to use 'aarch64-linux' because:
>
>   1. clang won't find the correct sysroot, at least on my system (it
> complains
>      that asm/errno.h can't no be founded).
>
>   2. It won't define __linux or __linux__ macros, which is used in some
> places
>      in the code.
>
> With my updated branch I could build to aarch64-linux with current llvm
> master
> (3c2a74a3ae02d16e899e280953c055f92aa6cdaa).
>
> >
> > The below error is reported:
> >
> > *make[2]: Entering directory '/home/glibc/glibc/csu'*
> > *clang --target=aarch64 -nostdlib -nostartfiles -r -o
> > /home/glibc/glibc/build/csu/crt1.o /home/glibc/glibc/build/csu/start.o
> > /home/glibc/glibc/build/csu/abi-note.o /home/glibc/glibc/build/csu/init.o
> > /home/glibc/glibc/build/csu/static-reloc.o*
> > *ld: error: /home/glibc/glibc/build/csu/start.o is incompatible with
> > elf_x86_64*
> > *ld: error: /home/glibc/glibc/build/csu/abi-note.o is incompatible with
> > elf_x86_64*
> > *ld: error: /home/glibc/glibc/build/csu/init.o is incompatible with
> > elf_x86_64*
> > *ld: error: /home/glibc/glibc/build/csu/static-reloc.o is incompatible
> with
> > elf_x86_64*
> > *collect2: error: ld returned 1 exit status*
> > *clang-13: error: linker (via gcc) command failed with exit code 1 (use
> -v
> > to see invocation)*
> > *make[2]: *** [Makefile:134: /home/glibc/glibc/build/csu/crt1.o] Error 1*
> > *make[2]: Leaving directory '/home/glibc/glibc/csu'*
> > *make[1]: *** [Makefile:483: csu/subdir_lib] Error 2*
> > *make[1]: Leaving directory '/home/glibc/glibc'*
> > *make: *** [Makefile:9: all] Error 2*
>
> I am almost sure this similar to error I saw trying to use just 'aarch64'
> triple.
>
> >
> > Then I run the above command manually by use -v, it reports as below:
> > *clang version 13.0.0*
> > *Target: aarch64*
> > *Thread model: posix*
> > *InstalledDir: /usr/local/bin*
> > * "/usr/bin/gcc" -nostdlib -nostartfiles -o
> > /home/glibc/glibc/build/csu/crt1.o -r /home/glibc/glibc/build/csu/start.o
> > /home/glibc/glibc/build/csu/abi-note.o /home/glibc/glibc/build/csu/init.o
> > /home/glibc/glibc/build/csu/static-reloc.o*
> > *ld: error: /home/glibc/glibc/build/csu/start.o is incompatible with
> > elf_x86_64*
> > *ld: error: /home/glibc/glibc/build/csu/abi-note.o is incompatible with
> > elf_x86_64*
> > *ld: error: /home/glibc/glibc/build/csu/init.o is incompatible with
> > elf_x86_64*
> > *ld: error: /home/glibc/glibc/build/csu/static-reloc.o is incompatible
> with
> > elf_x86_64*
> > *collect2: error: ld returned 1 exit status*
> > *clang-13: error: linker (via gcc) command failed with exit code 1 (use
> -v
> > to see invocation)*
> >
> > I think it's an issue on my computer that clang will not invoke ld.lld
> > correctly, it always run "/usr/bin/gcc" which I still can't fix. Then I
> try
> > this command by manually invoking the ld.lld directly but it still
> reports
> > error:
> > *root@6ab3fca322b6:/home/glibc/glibc/build# ld.lld -nostdlib
> -nostartfiles
> > -o /home/glibc/glibc/build/csu/crt1.o -r
> > /home/glibc/glibc/build/csu/start.o
> /home/glibc/glibc/build/csu/abi-note.o
> > /home/glibc/glibc/build/csu/init.o
> > /home/glibc/glibc/build/csu/static-reloc.o*
> > *ld.lld: error: unknown argument '-nostartfiles'*
> >
> > I think the issue is the flag'-nostartfiles', then I remove it and try
> the
> > below command it works:
> > *root@6ab3fca322b6:/home/glibc/glibc/build# ld.lld -nostdlib -o
> > /home/glibc/glibc/build/csu/crt1.o -r /home/glibc/glibc/build/csu/start.o
> > /home/glibc/glibc/b*
> > *uild/csu/abi-note.o /home/glibc/glibc/build/csu/init.o
> > /home/glibc/glibc/build/csu/static-reloc.o*
> > *root@6ab3fca322b6:/home/glibc/glibc/build#*
> >
> > My questions are as below:
> > 1. Is the below command correct to build the branch with clang for
> aarch64:
> > ../configure CC="clang --target=aarch64" CXX="clang++ --target=aarch64"
> > --target=aarch64 --host=aarch64-linux-gnu --disable-werror --prefix=/usr
> >
> > 2. Why clang failed to invoke ld.lld? I am using clang and ld.lld 13.0.0
> > and I build the llvm from source code.
> >
> > 3. Why the flag '-nostartfiles' is not supported by ld.lld? I find the
> > webpage "
> >
> https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-nostartfiles
> “
> > show that this flag is supported by clang?
>
> Although lld is currently support for build with gcc (at least for x86 and
> ARM),
> the issue seems related on recent --with-default-link [1].  So you will
> need to
> use 'yes' to build with lld:
>
> # Assuming 'ld' points to 'ld.lld' in you path
> $ configure --prefix=/usr \
>   --build=x86_64-linux-gnu \
>   --host=aarch64-linux-gnu \
>   --target=aarch64-linux-gnu \
>   CC="clang --target=aarch64-linux" \
>   CXX="clang++ --target=aarch64-linux" \
>   --with-default-link=yes
>
> It should build.  I have not yet tested if build all tests and the make
> check
> result, I only have done it with binutils.
>
>
> Btw, thanks for taking interest in this work.  I hope to get something
> 'upstreamable' in near future.
>
> [1] https://sourceware.org/pipermail/libc-alpha/2022-April/138260.html
>