[llvm-dev] conflicting builtins in clang with musl (stddef.h)

[Khem Raj via llvm-dev]

On Sat, Aug 3, 2019 at 6:51 AM David Demelier via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> Hello there,
>
> I'm building a Linux distribution based on musl and LLVM as default
> toolchain (including lld/libc++/libc++abi/libunwind rather than GNU).
> For most of the time this works pretty well.
>
> However I'm having troubles with few packages, webkit for instance
> fails because of max_align_t being redeclared in musl's stddef.h
>
> I see that stddef.h is provided by both musl and in the private clang
> include directories.
>
>     /include/stddef.h
>     /lib/clang/8.0.0/include/stddef.h
>
> Usually, compiling a sample program works:
>
> $ cat test.cpp
> #include <stddef.h>
> #include <limits>
> #include <type_traits>
>
> int main() {
> }
>
> $ clang++ -std=c++17 -v test.cpp
> Vanilla Linux clang version 8.0.0 (tags/RELEASE_800/final) (based on
> LLVM 8.0.0)
> Target: x86_64-unknown-linux-musl
> Thread model: posix
> InstalledDir: /bin
>  "/bin/clang-8" -cc1 -triple x86_64-unknown-linux-musl -emit-obj
> -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names
> -main-file-name test.cpp -mrelocation-model pic -pic-level 2 -pic-is-
> pie -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose
> -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-
> 64 -dwarf-column-info -debugger-tuning=gdb -v -resource-dir
> /lib/clang/8.0.0 -internal-isystem /bin/../include/c++/v1 -internal-
> isystem /usr/local/include -internal-isystem /lib/clang/8.0.0/include
> -internal-externc-isystem /include -internal-externc-isystem
> /usr/include -std=c++17 -fdeprecated-macro -fdebug-compilation-dir /tmp
> -ferror-limit 19 -fmessage-length 274 -fobjc-runtime=gcc -fcxx-
> exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics
> -o /tmp/test-0249b1.o -x c++ test.cpp -faddrsig
> clang -cc1 version 8.0.0 based upon LLVM 8.0.0 default target x86_64-
> linux-musl
> ignoring nonexistent directory "/usr/local/include"
> ignoring duplicate directory "/include"
> #include "..." search starts here:
> #include <...> search starts here:
>  /bin/../include/c++/v1
>  /lib/clang/8.0.0/include
>  /include
> End of search list.
>  "/bin/ld.lld" -pie --eh-frame-hdr -m elf_x86_64 -dynamic-linker
> /lib/ld-musl-x86_64.so.1 -o a.out /bin/../lib/Scrt1.o
> /bin/../lib/crti.o /lib/clang/8.0.0/lib/linux/crtbeginS.o -L/bin/../lib
> -L/lib -L/usr/lib /tmp/test-0249b1.o -lc++ -lm
> /lib/clang/8.0.0/lib/linux/libclang_rt.builtins-x86_64.a -lc
> /lib/clang/8.0.0/lib/linux/libclang_rt.builtins-x86_64.a
> /lib/clang/8.0.0/lib/linux/crtendS.o /bin/../lib/crtn.o
>
> However, webkit's CMake for some reasons adds -isystem /include which
> breaks the build with the error I mentioned above. I can reproduce it
> with this example of code too:
>
> $ clang++ -isystem /include -std=c++17 test.cpp
> In file included from test.cpp:2:
> In file included from /bin/../include/c++/v1/limits:106:
> In file included from /bin/../include/c++/v1/type_traits:406:
> In file included from /bin/../include/c++/v1/cstddef:45:
> In file included from /lib/clang/8.0.0/include/stddef.h:118:
> /lib/clang/8.0.0/include/__stddef_max_align_t.h:40:3: error: typedef
> redefinition with different types ('struct max_align_t' vs 'struct
> max_align_t')
> } max_align_t;
>   ^
> /include/bits/alltypes.h:49:54: note: previous definition is here
> typedef struct { long long __ll; long double __ld; } max_align_t;
>                                                      ^
> 1 error generated.
>
> I've asked to the musl's maintainer and said that clang should not
> provide std* files that are already present in musl. He also said that
> the include order should be inversed to use '/include' first. I've
> checked FreeBSD which also use clang and they effectively removed
> stddef.h and all headers that are already provided by their own libc.
>
> So I've tried to remove them temporarily but now, it's the opposite.
> webkit fails to find stddef.h even though it's provided by musl in
> /include/stddef.h.
>
> # clang++ -std=c++17 -isystem /include test.cpp
> In file included from test.cpp:2:
> In file included from /bin/../include/c++/v1/limits:106:
> In file included from /bin/../include/c++/v1/type_traits:406:
> /bin/../include/c++/v1/cstddef:45:15: fatal error: 'stddef.h' file not
> found
> #include_next <stddef.h>
>               ^~~~~~~~~~
> 1 error generated.
>
> I'm scratching my hair trying to understand what is wrong and what
> should I do here.
>
> Also, I can't understand why CMake adds all these -isystem include
> directories. But this is a webkit issue I guess.
>
> Any ideas/recommandations are welcome.
>

you might want to look at the patches we have for webkit

https://git.openembedded.org/openembedded-core/tree/meta/recipes-sato/webkit/webkitgtk

especially
https://git.openembedded.org/openembedded-core/tree/meta/recipes-sato/webkit/webkitgtk/0001-Fix-build-with-musl.patch
https://git.openembedded.org/openembedded-core/tree/meta/recipes-sato/webkit/webkitgtk/0001-WebKitMacros-Append-to-I-and-not-to-isystem.patch

the second patch will help solve your current problem, but there will
be more down the line :)

We have a layer for Yocto/OE which builds a linux distribution in a
cross environment using clang + clang-runtime + musl as you are using.
It might be useful for you
in what you are doing. See

https://github.com/kraj/meta-clang

if you want latest 9.0-rc stuff then its in kraj/master branch

> Kind regards,
>
> --
> David
>
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