[cfe-dev] Problem linking in some dataflow sanitizer functions?

Mon Jan 12 14:10:25 PST 2015

Hi Christian,

If you wish to compile C++ programs with DFSan, you will first need to
compile the C++ standard library with DFSan. Unfortunately, the way to do
this is quite painful at the moment, and needs to be simplified and documented
better. This way worked for me:

1. Check out the libcxx and libcxxabi projects into the LLVM projects directory.

2. Use cmake to configure a separate build directory in which to build libcxx
   and libcxxabi with DFSan:

    # assuming that your LLVM source directory is ~/src/llvm and build directory is ~/src/llvm-build
    mkdir ~/src/llvm-build-dfsan
    cd ~/src/llvm-build-dfsan
    CC=~/src/llvm-build/bin/clang CXX=~/src/llvm-build/bin/clang++ cmake -G Ninja ../llvm -DCMAKE_C_FLAGS=-fsanitize=dataflow -DCMAKE_CXX_FLAGS=-fsanitize=dataflow -DLIBCXXABI_ENABLE_SHARED=NO -DLIBCXX_ENABLE_SHARED=NO -DLLVM_FORCE_USE_OLD_TOOLCHAIN=YES -DLIBCXX_CXX_ABI=libcxxabi

3. Build only libc++ and libc++abi in the just-configured build directory:
    ninja cxx cxxabi

3. To compile your program, pass the following flags to clang++:

   compile flags: -stdlib=libc++ -fsanitize=dataflow -I$HOME/src/llvm-build-dfsan/include/c++/v1
   link flags: -stdlib=libc++ -fsanitize=dataflow -L$HOME/src/llvm-build-dfsan/lib -Wl,--start-group,-lc++abi

I was able to compile and run your hello world program this way. Please let
me know if it works for you.

Thanks,
Peter

On Mon, Jan 12, 2015 at 04:25:48PM -0500, Christian Convey wrote:
> Thanks Peter.  That seems to have done the trick for dfsan_get_label_info.
> 
> I'm still having trouble with C++ STL functions, though.  Any idea why
> I might be getting the following?
> 
> I have this simple test program, foo2.c:
> >>>>>
> #include <iostream>
> 
> using namespace std;
> 
> int main(void) {
>     cout << "Hellow, world!" << endl;
>     return 0;
> }
> <<<<<
> 
> When I build it without the dataflow sanitizer, things work fine:
> /home/cconvey/dw/clang-llvm-git/build/bin/clang++ -std=c++11  foo2.cpp
> 
> However, when I enable the sanitizer, there are a lot of unmet
> dependencies.  Any idea if I'm doing something wrong on the command
> line?
> cconvey at spaceman /tmp $
> /home/cconvey/dw/clang-llvm-git/build/bin/clang++ -std=c++11
> -fsanitize=dataflow foo2.cpp
> /tmp/foo2-8b9f0f.o: In function `main':
> foo2.cpp:(.text+0xb): undefined reference to
> `dfs$_ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_'
> foo2.cpp:(.text+0x44): undefined reference to
> `dfs$_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc'
> foo2.cpp:(.text+0x6a): undefined reference to `dfs$_ZNSolsEPFRSoS_E'
> /tmp/foo2-8b9f0f.o: In function `dfs$__cxx_global_var_init':
> foo2.cpp:(.text.startup+0x1d): undefined reference to
> `dfs$_ZNSt8ios_base4InitC1Ev'
> foo2.cpp:(.text.startup+0x24): undefined reference to
> `dfs$_ZNSt8ios_base4InitD1Ev'
> clang-3.6: error: linker command failed with exit code 1 (use -v to
> see invocation)
> 
> 
> Thanks,
> Christian
> 
> On Mon, Jan 12, 2015 at 3:43 PM, Peter Collingbourne <peter at pcc.me.uk> wrote:
> > Hi Christian,
> >
> > There was a bug that prevented clients from using the dfsan_get_label_info
> > function. That bug is now fixed in compiler-rt r225692.
> >
> > Peter
> >
> > On Mon, Jan 12, 2015 at 12:56:01PM -0500, Christian Convey wrote:
> >> Hello, I'm using the dataflow sanitizer in clang 3.6 for the first
> >> time, I'm I'm running into some linker errors.  I was wondering if
> >> someone could point out my mistake?
> >>
> >> I downloaded (today) from git the current llvm, clang, and compiler-rt
> >> code.  It built without any problem.
> >>
> >> Using that build of clang/llvm, I'm able to run the example code shown
> >> here:  http://clang.llvm.org/docs/DataFlowSanitizer.html#example
> >>
> >> However, I have a linking problem when I try to extend the example.
> >> When I try to call the function "dfsan_get_label_info", the linker
> >> can't find it.  This is a bit of a surprise, because it does appear to
> >> be defined in my LLVM build:
> >>
> >> cconvey at spaceman /tmp $ nm
> >> /home/cconvey/dw/clang-llvm-git/build/bin/../lib/clang/3.6.0/lib/linux/libclang_rt.dfsan-x86_64.a
> >> | grep dfsan_get_label_info
> >> 0000000000000990 T _Z20dfsan_get_label_infot
> >> cconvey at spaceman /tmp $ c++filt _Z20dfsan_get_label_infot
> >> dfsan_get_label_info(unsigned short)
> >>
> >> And I'm reasonably sure I'm linking in that .a file:
> >>
> >> cconvey at spaceman /tmp $
> >> /home/cconvey/dw/clang-llvm-git/build/bin/clang  -fsanitize=dataflow
> >> foo.c -v
> >> clang version 3.6.0 (http://llvm.org/git/clang.git
> >> 48d2f2367001a51a3253cc34aea4a91c92fd45fb)
> >> (http://llvm.org/git/llvm.git
> >> ad017096fc8eec5afd256f572d8d0b9d5d8aa09f)
> >> ...
> >> End of search list.
> >>  "/usr/bin/ld" -pie --eh-frame-hdr -m elf_x86_64 -dynamic-linker
> >> /lib64/ld-linux-x86-64.so.2 -o a.out
> >> /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/Scrt1.o
> >> /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crti.o
> >> /usr/lib/gcc/x86_64-linux-gnu/4.8/crtbeginS.o
> >> -L/usr/lib/gcc/x86_64-linux-gnu/4.8
> >> -L/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu
> >> -L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu
> >> -L/usr/lib/gcc/x86_64-linux-gnu/4.8/../../..
> >> -L/home/cconvey/dw/clang-llvm-git/build/bin/../lib -L/lib -L/usr/lib
> >> -whole-archive /home/cconvey/dw/clang-llvm-git/build/bin/../lib/clang/3.6.0/lib/linux/libclang_rt.dfsan-x86_64.a
> >> -no-whole-archive
> >> --dynamic-list=/home/cconvey/dw/clang-llvm-git/build/bin/../lib/clang/3.6.0/lib/linux/libclang_rt.dfsan-x86_64.a.syms
> >> /tmp/foo-5310a2.o --no-as-needed -lpthread -lrt -lm -ldl -lgcc
> >> --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s
> >> --no-as-needed /usr/lib/gcc/x86_64-linux-gnu/4.8/crtendS.o
> >> /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crtn.o
> >> /tmp/foo-5310a2.o: In function `dfs$execute_tree':
> >> foo.c:(.text+0xa89): undefined reference to `dfsan_get_label_info'
> >> /tmp/foo-5310a2.o: In function `dfsw$dfsan_get_label_info':
> >> foo.c:(.text.dfsw$dfsan_get_label_info[dfsw$dfsan_get_label_info]+0xb):
> >> undefined reference to `dfsan_get_label_info'
> >> clang-3.6: error: linker command failed with exit code 1 (use -v to
> >> see invocation)
> >> cconvey at spaceman /tmp $
> >>
> >> (I'm also having linkage problems when my code uses C++ iostreams, but
> >> I figured I'd work through this issue first.)
> >> _______________________________________________
> >> cfe-dev mailing list
> >> cfe-dev at cs.uiuc.edu
> >> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >>
> >
> > --
> > Peter
> 

-- 
Peter