fabic974 random (binary) wanderings in the philament empires…

LLVM Clang: Building it from scratch - take 2 (ok)

Trying to proceed the CMake-based build that failed yesterday – Huh! 2 GB of resident memory while linking clang target, and with only 4 GB of total RAM, my laptop ends up using all the 4 GB swap – killing some processes – possibly too late: link failled with the same “undefined symbols” reason.

Rebooting laptop – trying again from console mode – got loads of free mem. – linker quickly jumps up using 2 GB of memory, not swaping this time and 2 GB seems to be the peak mem. needed for this target – 3 minutes of work and… failed with the same errors – ok that wasn’t due to some obscur “bug” possibly related to memory exhaustion.

Re-trying, bootstrapping Clang with yesterdays build

Ok, restarting from scratch, – from console-mode –, but this time I’m using my yesterday’s build of Clang (which is linked against libgcc & libstdc++) to bootstrap this one :

# Mostly successful build using ../llvm/configure :
mv build build__conf
mkdir build
cd build/

export PATH=$PWD/build__conf/Release+Asserts/bin:$PATH

CC=clang CXX=clang++ ; export CC CXX ; env|grep clang ; which clang

cmake ../llvm/

time make -j3 -l4

lunch break

48% built after 1 hour or so, 1.4 GB free mem. + 1.8 GB cached & no swap used, 15 min. load average is 2.75, ok.

Wandering ‘round – reading man vfork – I’m a bit dizzy – something like 2h20 to go – nap break!

Back from nap ~1hr – 98% done, fingers-crossed – libclang.so is being linked, target clang just started! – free mem. is dropping fast: can now see the linker process peaking a 2 GB memory – little swapping occurs (other jobs running too) – ld process peaks at 2.2 GB, and disappeared! Great!: [ 98%] Built target clang ;-)

Damn :/ can’t find clang binary under bin/ – worried – make is at 100% performing stuff about libcxx_tsan/msanfind -type f -perm -u+x |sort: no clang anywhere :/ I hope this is due to some yet uncompleted build steps – wating…

Argh! I was searching for it in yesterday’s failled build dir. -_-

Build completed, ok.

libcxx any ?

Nope, it linked itself against the host’s libgcc & libstdc++ libs. ; since libc++.so was built I was expecting that Clang would build itself against it magically, but it did not :

[fabi@wall] ~/dev/llvm/build2 (master ■)  ldd bin/clang
        linux-vdso.so.1 (0x00007fffcdbfe000)
        librt.so.1 => /lib64/librt.so.1 (0x00007ffb15492000)
        libdl.so.2 => /lib64/libdl.so.2 (0x00007ffb1528e000)
        libncurses.so.5 => /lib64/libncurses.so.5 (0x00007ffb15038000)
        libpthread.so.0 => /lib64/libpthread.so.0 (0x00007ffb14e1b000)
        libz.so.1 => /lib64/libz.so.1 (0x00007ffb14c05000)
        libstdc++.so.6 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.7.3/libstdc++.so.6 (0x00007ffb148e3000)
        libm.so.6 => /lib64/libm.so.6 (0x00007ffb145e5000)
        libgcc_s.so.1 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.7.3/libgcc_s.so.1 (0x00007ffb143ce000)
        libc.so.6 => /lib64/libc.so.6 (0x00007ffb1401e000)
        /lib64/ld-linux-x86-64.so.2 (0x00007ffb1569a000)

This is fine though since I now know that I can have a full make all run that completes w/o errors, and I have a clean Clang 3.5.0 toolchain for proceeding with further experiments.


  • Build LLVM/Clang with ../llvm/configure && make -j3 -l3 so as to obtain a working toolchain (with possibly a few minor targets that fail in clang-tools-extra) ;
  • Bootstrap-build again using this fresh Clang.

Some brief testing

hello world++

[fabi@wall] ~/dev/llvm (master ✗)  cat > test.cpp <<EOF
/** File: test.cpp

#include <iostream>

using std::cout;

int main(int argc, char *argv[])
    int arr[3] = {1,2,3};
    for(auto i : arr)
        cout << i << ": Hello dude!\n";
    return 127;

Builds, ok :

[fabi@wall] ~/dev/llvm (master ✗)  clang++ -std=c++11 test.cpp

[fabi@wall] ~/dev/llvm (master ✗)  ./a.out ; echo $?
1: Hello dude!
2: Hello dude!
3: Hello dude!

It got linked with libstdc++ & libgcc_s as expected :

[fabi@wall] ~/dev/llvm (master ✗)  ldd a.out
    linux-vdso.so.1 (0x00007fffff1fe000)
    libstdc++.so.6 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.7.3/libstdc++.so.6 (0x00007f4741996000)
    libm.so.6 => /lib64/libm.so.6 (0x00007f4741698000)
    libgcc_s.so.1 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.7.3/libgcc_s.so.1 (0x00007f4741481000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f47410d1000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f4741cb8000)

With -stdlib=c++

[fabi@wall] ~/dev/llvm (master ✗)  clang++ -std=c++11 -stdlib=libc++ test.cpp
test.cpp:9:10: fatal error: 'iostream' file not found
#include <iostream>
1 error generated.

Ok with -lc++abi and specifying libcxx’s include path :

[fabi@wall] ~/dev/llvm (master ✗)  clang++ -std=c++11 -stdlib=libc++ \
    -Illvm/projects/libcxx/include/ \
    -lc++abi \
    -v test.cpp

Ok too as per http://libcxx.llvm.org/ :

[fabi@wall] ~/dev/llvm (master ✗)  clang++ -std=c++11 -stdlib=libc++ \
    -Illvm/projects/libcxx/include/ \
    -nodefaultlibs -lc++ -lc++abi -lm -lc -lgcc_s -lgcc \

[fabi@wall] ~/dev/llvm (master ✗)  ldd ./a.out
    linux-vdso.so.1 (0x00007fffcdd69000)
    libc++.so.1 => not found
    libc++abi.so.1 => not found
    libm.so.6 => /lib64/libm.so.6 (0x00007f643ff30000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f643fb80000)
    libgcc_s.so.1 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.7.3/libgcc_s.so.1 (0x00007f643f969000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f644022e000)

Ok, it runs :

[fabi@wall] ~/dev/llvm (master ✗)  export LD_LIBRARY_PATH=$PWD/build/lib

[fabi@wall] ~/dev/llvm (master ✗)  ldd ./a.out
    linux-vdso.so.1 (0x00007fff34fc8000)
    libc++.so.1 => /home/fabi/dev/llvm/build/lib/libc++.so.1 (0x00007f2f94f31000)
    libc++abi.so.1 => /home/fabi/dev/llvm/build/lib/libc++abi.so.1 (0x00007f2f94cae000)
    libm.so.6 => /lib64/libm.so.6 (0x00007f2f949b0000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f2f94600000)
    libgcc_s.so.1 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.7.3/libgcc_s.so.1 (0x00007f2f943e9000)
    libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f2f941cc000)
    librt.so.1 => /lib64/librt.so.1 (0x00007f2f93fc4000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f2f952cf000)

[fabi@wall] ~/dev/llvm (master ✗)  ./a.out
1: Hello dude!
2: Hello dude!
3: Hello dude!

Also ok if hard-coding library path with -Wl,-rpath=$PWD/local/lib test.cpp :

[fabi@wall] ~/dev/llvm (master ✗)  clang++ -std=c++11 -stdlib=libc++ \
    -nodefaultlibs -lc++ -lc++abi -lm -lc -lgcc_s -lgcc \
    -Wl,-rpath=$PWD/local/lib test.cpp

[fabi@wall] ~/dev/llvm (master ✗)  ldd ./a.out
    linux-vdso.so.1 (0x00007fff4d597000)
    libc++.so.1 => /home/fabi/dev/llvm/local/lib/libc++.so.1 (0x00007f78864de000)
    libc++abi.so.1 => /home/fabi/dev/llvm/local/lib/libc++abi.so.1 (0x00007f788625b000)
    libm.so.6 => /lib64/libm.so.6 (0x00007f7885f5d000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f7885bad000)
    libgcc_s.so.1 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.7.3/libgcc_s.so.1 (0x00007f7885996000)
    libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f7885779000)
    librt.so.1 => /lib64/librt.so.1 (0x00007f7885571000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f788687c000)


It seems I have a good starting point for playing around with compiling stuff against libcxx/abi ;- under Linux…

End of transmission.