[llvm-dev] Failed to configure LLVM for use with Musl

[Vedant Kumar via llvm-dev]

> On Dec 2, 2016, at 4:57 AM, Dmitry Golovin via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> I want to build LLVM-based toolchain with Musl, I have LLVM sources with clang and lld (under `tools` directory) and libunwind, compiler-rt, libcxx and libcxxabi (under `projects` directory). All are the latest versions cloned from GitHub mirror, branch `master`.
> 
> I'm trying to configure with the following options:
>    CLANG_DEFAULT_CXX_STDLIB = libc++
>    CLANG_DEFAULT_RTLIB = compiler-rt
>    LIBCXX_CXX_ABI = libcxxabi
>    LLVM_DEFAULT_TARGET_TRIPLE = x86_64-pc-linux-musl
>    LIBCXXABI_TARGET_TRIPLE = x86_64-pc-linux-musl
>    LIBUNWIND_TARGET_TRIPLE = x86_64-pc-linux-musl
>    DEFAULT_SYSROOT = /path/to/musl
>    GCC_INSTALL_PREFIX = /path/to/gcc-stub
>    LLVM_TARGETS_TO_BUILD = X86
>    LIBCXXABI_USE_COMPILER_RT = ON
>    LIBCXXABI_USE_LLVM_UNWINDER = ON
>    LIBCXX_HAS_MUSL_LIBC = ON
>    LIBCXX_USE_COMPILER_RT = ON
>    LLVM_ENABLE_LIBCXX = ON
>    LLVM_ENABLE_LLD = ON
> 
> When I try to configure, I get the following error messages:
> 
> CMake Warning at cmake/modules/HandleLLVMStdlib.cmake:24 (message):
>   Can't specify libc++ with '-stdlib='
> Call Stack (most recent call first):
>   cmake/config-ix.cmake:15 (include)
>   CMakeLists.txt:566 (include)

^ This seems harmless. You'll probably end up building with libstdc++.

> 
> CMake Error at projects/libunwind/src/CMakeLists.txt:70 (message):
>   Compiler doesn't support generation of unwind tables if exception support
>   is disabled.  Building libunwind DSO with runtime dependency on C++ ABI
>   library is not supported.

It looks like your host compiler doesn't support -funwind-tables.

Try building with clang?

I've CC'd Saleem who might know more about this.

best,
vedant

> 
> I'm probably doing something wrong, but I can't figure out what exactly. If I omit some of the flags, I get different errors, but I never get successful configuration.
> 
> I'm on Ubuntu 16.04 (if it is important) and have not yet tried on other machines, but I'm pretty sure it is possible to reproduce it.
> 
> Regards,
> Dmitry Golovin
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