[cfe-dev] clang confused by GCC 8

Tue Nov 28 01:27:33 PST 2017

Hi all,

After building and installing GCC trunk (GCC 8), clang doesn't find
the Standard C++ Library any more:

/tmp$ cat > strm.cpp
#include <iostream>
^D

/tmp$ /usr/local/bin/clang++ -v strm.cpp
clang version 6.0.0 (trunk 319018)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.2.0
Found candidate GCC installation:
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/8.0.0
Selected GCC installation: /usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/8.0.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
 "/usr/local/bin/clang-6.0" -cc1 -triple x86_64-unknown-linux-gnu
-emit-obj -mrelax-all -disable-free -main-file-name strm.cpp
-mrelocation-model static -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 /usr/local/lib/clang/6.0.0
-internal-isystem /usr/local/include -internal-isystem
/usr/local/lib/clang/6.0.0/include -internal-externc-isystem
/usr/include/x86_64-linux-gnu -internal-externc-isystem /include
-internal-externc-isystem /usr/include -fdeprecated-macro
-fdebug-compilation-dir /tmp -ferror-limit 19 -fmessage-length 271
-fobjc-runtime=gcc -fcxx-exceptions -fexceptions
-fdiagnostics-show-option -fcolor-diagnostics -o /tmp/strm-ba92aa.o -x
c++ strm.cpp
clang -cc1 version 6.0.0 based upon LLVM 6.0.0svn default target
x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/local/lib/clang/6.0.0/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
strm.cpp:1:10: fatal error: 'iostream' file not found
#include <iostream>
         ^~~~~~~~~~

For some reason, GCC8's include directories are not used, despite
"Selected GCC installation:
/usr/local/bin/../lib/gcc/x86_64-pc-linux-gnu/8.0.0". Not even
``ignoring nonexistent directory`` is printed (unless the ``ignoring
nonexistent directory "/include" `` was clang's attempt to use the
GCC8 installation).

$ find /usr/local/lib/gcc/x86_64-pc-linux-gnu/8.0.0/ -name iostream
/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.0.0/include/c++/iostream

If I hide /usr/local/lib/gcc/x86_64-pc-linux-gnu/8.0.0 (to simulate
the state before I built and installed GCC 8), then it works:

/tmp$ /usr/local/bin/clang++ -v strm.cpp
clang version 6.0.0 (trunk 319018)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.2.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.2.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
 "/usr/local/bin/clang-6.0" -cc1 -triple x86_64-unknown-linux-gnu
-emit-obj -mrelax-all -disable-free -main-file-name strm.cpp
-mrelocation-model static -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 /usr/local/lib/clang/6.0.0
-internal-isystem
/usr/lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0
-internal-isystem
/usr/lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/x86_64-linux-gnu/c++/7.2.0
-internal-isystem
/usr/lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/x86_64-linux-gnu/c++/7.2.0
-internal-isystem
/usr/lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/backward
-internal-isystem /usr/local/include -internal-isystem
/usr/local/lib/clang/6.0.0/include -internal-externc-isystem
/usr/include/x86_64-linux-gnu -internal-externc-isystem /include
-internal-externc-isystem /usr/include -fdeprecated-macro
-fdebug-compilation-dir /tmp -ferror-limit 19 -fmessage-length 271
-fobjc-runtime=gcc -fcxx-exceptions -fexceptions
-fdiagnostics-show-option -fcolor-diagnostics -o /tmp/strm-c79a25.o -x
c++ strm.cpp
clang -cc1 version 6.0.0 based upon LLVM 6.0.0svn default target
x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
ignoring duplicate directory
"/usr/lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/x86_64-linux-gnu/c++/7.2.0"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0
 /usr/lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/x86_64-linux-gnu/c++/7.2.0
 /usr/lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/backward
 /usr/local/include
 /usr/local/lib/clang/6.0.0/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
(success)

I tried passing --gcc-toolchain set to the directory selected in the
absence of GCC 8, but it didn't work. The only effect seems to be to
stop searching for GCC installations :

/tmp$ /usr/local/bin/clang++
--gcc-toolchain=/usr/lib/gcc/x86_64-linux-gnu/7.2.0 -v strm.cpp
clang version 6.0.0 (trunk 319018)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
 "/usr/local/bin/clang-6.0" -cc1 -triple x86_64-unknown-linux-gnu
-emit-obj -mrelax-all -disable-free -main-file-name strm.cpp
-mrelocation-model static -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 /usr/local/lib/clang/6.0.0
-internal-isystem /usr/local/include -internal-isystem
/usr/local/lib/clang/6.0.0/include -internal-externc-isystem
/usr/include/x86_64-linux-gnu -internal-externc-isystem /include
-internal-externc-isystem /usr/include -fdeprecated-macro
-fdebug-compilation-dir /tmp -ferror-limit 19 -fmessage-length 271
-fobjc-runtime=gcc -fcxx-exceptions -fexceptions
-fdiagnostics-show-option -fcolor-diagnostics -o /tmp/strm-241a36.o -x
c++ strm.cpp
clang -cc1 version 6.0.0 based upon LLVM 6.0.0svn default target
x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/local/lib/clang/6.0.0/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
strm.cpp:1:10: fatal error: 'iostream' file not found
#include <iostream>
         ^~~~~~~~~~

This is an Ubuntu 17.10 machine whose system compiler is GCC 7.2:

/tmp$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
7.2.0-8ubuntu3' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++
--prefix=/usr --with-gcc-major-version-only --program-suffix=-7
--program-prefix=x86_64-linux-gnu- --enable-shared
--enable-linker-build-id --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --libdir=/usr/lib
--enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin
--enable-default-pie --with-system-zlib --with-target-system-zlib
--enable-objc-gc=auto --enable-multiarch --disable-werror
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 7.2.0 (Ubuntu 7.2.0-8ubuntu3)

This is how GCC 8 was configured:

/tmp$ g++-8 -v
Using built-in specs.
COLLECT_GCC=g++-8
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-pc-linux-gnu/8.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../trunk/configure --program-suffix=-8
--enable-version-specific-runtime-libs --enable-languages=c,c++,lto :
(reconfigured) ../trunk/configure --program-suffix=-8
--enable-version-specific-runtime-libs --enable-languages=c,c++,lto
Thread model: posix
gcc version 8.0.0 20171124 (experimental) (GCC)

Any ideas?

Csaba
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