[cfe-dev] libc++: Unexpected pointer-to-member-function behavior

[David Blaikie via cfe-dev]

FWIW the C++ standard doesn't allow taking the address of standard library
member functions (I don't know the wording - but I can go hunt for it), so
far as I understand.

That said, interesting failure - not what I'd have expected.

On Thu, Apr 20, 2017 at 10:45 PM Adam C. Emerson via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hello. I'm not sure if this is a bug or if I'm using undefined
> behavior or otherwise doing something screwy.
>
> My Minimal Working Reproducer is:
>
> ---------->8-----------
>
> #include <functional>
> #include <iostream>
> #include <string>
>
> int main(void) {
>     auto s = ::std::string("Meow.");
>     auto l = ::std::mem_fn(&::std::string::size);
>
>     ::std::cout << l(s) << ::std::endl;
>
>     return 0;
> }
>
> ---------->8-----------
>
> If I compile this under g++ or with clang++ using libstdc++, this
> compiles and works as expected. However, if I use clang++ (v4.0.0 on
> Arch Linux x86_64) with libc++ (4.0.0), I get a link error:
>
> ---------->8-----------
>
> % clang++ -v -std=c++14 -stdlib=libc++ foo.cc
> clang version 4.0.0 (tags/RELEASE_400/final)
> Target: x86_64-unknown-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/x86_64-pc-linux-gnu/6.3.1
> Found candidate GCC installation:
> /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1
> Found candidate GCC installation: /usr/lib/gcc/x86_64-pc-linux-gnu/6.3.1
> Found candidate GCC installation: /usr/lib64/gcc/x86_64-pc-linux-gnu/6.3.1
> Selected GCC installation: /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1
> Candidate multilib: .;@m64
> Candidate multilib: 32;@m32
> Selected multilib: .;@m64
>  "/usr/bin/clang-4.0" -cc1 -triple x86_64-unknown-linux-gnu -emit-obj
> -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names
> -main-file-name foo.cc -mrelocation-model static -mthread-model posix
> -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases
> -munwind-tables -fuse-init-array -target-cpu x86-64 -v -dwarf-column-info
> -debugger-tuning=gdb -resource-dir /usr/bin/../lib/clang/4.0.0
> -internal-isystem /usr/bin/../include/c++/v1 -internal-isystem
> /usr/local/include -internal-isystem /usr/bin/../lib/clang/4.0.0/include
> -internal-externc-isystem /include -internal-externc-isystem /usr/include
> -std=c++14 -fdeprecated-macro -fdebug-compilation-dir /home/azure
> -ferror-limit 19 -fmessage-length 119 -fobjc-runtime=gcc -fcxx-exceptions
> -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -o
> /tmp/foo-1fe78b.o -x c++ foo.cc
> clang -cc1 version 4.0.0 based upon LLVM 4.0.0 default target
> x86_64-unknown-linux-gnu
> ignoring nonexistent directory "/include"
> #include "..." search starts here:
> #include <...> search starts here:
>  /usr/bin/../include/c++/v1
>  /usr/local/include
>  /usr/bin/../lib/clang/4.0.0/include
>  /usr/include
> End of search list.
>  "/usr/bin/ld" --eh-frame-hdr -m elf_x86_64 -dynamic-linker
> /lib64/ld-linux-x86-64.so.2 -o a.out
> /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../lib64/crt1.o
> /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../lib64/crti.o
> /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/crtbegin.o
> -L/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1
> -L/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../lib64
> -L/usr/bin/../lib64 -L/lib/../lib64 -L/usr/lib/../lib64
> -L/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../..
> -L/usr/bin/../lib -L/lib -L/usr/lib /tmp/foo-1fe78b.o -lc++ -lm -lgcc_s
> -lgcc -lc -lgcc_s -lgcc
> /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/crtend.o
> /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../lib64/crtn.o
> /tmp/foo-1fe78b.o: In function `main':
> foo.cc:(.text+0x44d): undefined reference to `std::__1::basic_string<char,
> std::__1::char_traits<char>, std::__1::allocator<char> >::size() const'
> /usr/bin/ld: a.out: hidden symbol
> `_ZNKSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE4sizeEv'
> isn't defined
> /usr/bin/ld: final link failed: Bad value
> clang-4.0: error: linker command failed with exit code 1 (use -v to see
> invocation)
>
> ---------->8-----------
>
> Thank you very much.
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