[PATCH] D23791: [libc++] Perform configuration checks with -nodefaultlibs

[Eric Fiselier via cfe-commits]

What platforms was this tested on?

On Aug 22, 2016 9:20 PM, "Shoaib Meenai" <smeenai at fb.com> wrote:

> smeenai created this revision.
> smeenai added reviewers: beanz, compnerd, EricWF, mclow.lists, rsmith.
> smeenai added a subscriber: cfe-commits.
>
> We're compiling libc++ with -nodefaultlibs, so we should also pass this
> option during the configuration checks to ensure those checks are
> consistent with the actual build.
>
> The primary motivation here is to ease cross-compilation against a
> non-standard set of C++ libraries. Previously, the configuration checks
> would attempt to link against the standard C++ libraries, which would
> cause link failures when cross-compiling, even though the actual library
> link would go through correctly (because of the use of -nodefaultlibs
> and explicitly specifying any needed libraries). This is more correct
> even ignoring the motivation, however.
>
> https://reviews.llvm.org/D23791
>
> Files:
>   cmake/config-ix.cmake
>
> Index: cmake/config-ix.cmake
> ===================================================================
> --- cmake/config-ix.cmake
> +++ cmake/config-ix.cmake
> @@ -1,5 +1,26 @@
>  include(CheckLibraryExists)
>  include(CheckCXXCompilerFlag)
> +
> +check_library_exists(c fopen "" LIBCXX_HAS_C_LIB)
> +check_library_exists(gcc_s __gcc_personality_v0 "" LIBCXX_HAS_GCC_S_LIB)
> +
> +# libc++ is built with -nodefaultlibs, so we want all our checks to also
> +# use this option, otherwise we may end up with an inconsistency between
> +# the flags we think we require during configuration (if the checks are
> +# performed without -nodefaultlibs) and the flags that are actually
> +# required during compilation (which has the -nodefaultlibs). libc is
> +# required for the link to go through.
> +check_cxx_compiler_flag(-nodefaultlibs LIBCXX_SUPPORTS_NODEFAULTLIBS_
> FLAG)
> +if (LIBCXX_SUPPORTS_NODEFAULTLIBS_FLAG)
> +  list(APPEND CMAKE_REQUIRED_LIBRARIES -nodefaultlibs)
> +  if (LIBCXX_HAS_C_LIB)
> +    list(APPEND CMAKE_REQUIRED_LIBRARIES c)
> +  endif ()
> +  if (LIBCXX_HAS_GCC_S_LIB)
> +    list(APPEND CMAKE_REQUIRED_LIBRARIES gcc_s)
> +  endif ()
> +endif ()
> +
>  include(CheckLibcxxAtomic)
>
>  # Check compiler flags
> @@ -14,7 +35,5 @@
>
>  # Check libraries
>  check_library_exists(pthread pthread_create "" LIBCXX_HAS_PTHREAD_LIB)
> -check_library_exists(c fopen "" LIBCXX_HAS_C_LIB)
>  check_library_exists(m ccos "" LIBCXX_HAS_M_LIB)
>  check_library_exists(rt clock_gettime "" LIBCXX_HAS_RT_LIB)
> -check_library_exists(gcc_s __gcc_personality_v0 "" LIBCXX_HAS_GCC_S_LIB)
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20160822/efbea12c/attachment.html>