[llvm-dev] How to compile glibc with clang/llvm?

Kristina Brooks via llvm-dev llvm-dev at lists.llvm.org
Sun Dec 23 02:59:43 PST 2018


Actually from reading the README, it seems to imply that it can be built
with Clang 6.0.0 and above now, though it does incorporate a lot of patches not
specific to Clang building so you will end up with them as well:


GRTE v5 and later can also be built with clang and (optionally) lld.
LLVM support for GNU source code continues to evolve (as of June
2018), so the process is less straightforward, and likely to change
from what is documented here.  There are a number of glibc patches
that make this work, including additional configure options mentioned

The minimum version of clang is 6.0.0.  If lld is to be used for linking,
it needs to be newer than 6.0.0.


  CC=path-to-llvm/clang CXX=path-to-llvm/clang++ \
    ../glibc/configure --disable-werror --with-clang --disable-float128 \
      --with-lld --with-default-link --disable-multi-arch --prefix=/something

On 23/12/2018 02:51, Kristina Brooks wrote:
> Hi.
> I've managed to do it before, with a lot of patches to Glibc, as well as ld.so and getting basic programs to start with
> it. However, a lot of tests did not pass and in general I abandoned it due to the fact that Glibc source code is not
> very easy to work with.
> I can upload it somewhere, not sure if there is any general interest in this kind of thing. I think current GRTE may
> also be build-able with Clang (my fork was based on older GRTE which had unfinished patches to support Clang), though I
> haven't had the time to look at that recently.
> I should add a huge disclaimer: this won't be easy and requires understanding the macro hell in glibc, GRTE relies on
> some hacky uses of `_Pragma` to supplement for some macros otherwise not possible with Clang. Even if you do get it to
> build I think it may be a waste of time to try and just implement the missing symbols in your case (or figure out why
> they're not being exported).
> Thanks.
> On 22/12/2018 09:29, xuruobin via llvm-dev wrote:
>> To whom it may concern,
>>  	Is there a way to build glibc with clang/llvm? I’m working on enabling llvm-cov for my compiler which is a totally new arch with a libc.a built from newlib. I successfully built compiler-rt but when I typed the command ` clang++ --target=xxx -fprofile-instr-generate -fcoverage-mapping foo.cc -o foo`, the linker failed because of undefined reference to `mmap'/`ftruncate'/`mkdir'. I found these functions are supported by glibc but I cannot bulid glibc with clang/llvm(configure gave me an error “These critical programs are missing or too old: compiler”). So I want to know how can I compile glibc with clang/llvm or are there some WIP patches to help me with this requirement?
>> Thanks,
>> Ruobin.
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

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