[Bug c++/77316] New: Unnecessary template copy constructor weak symbol emitted in wrong section

["rbd at debian dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77316

            Bug ID: 77316
           Summary: Unnecessary template copy constructor weak symbol
                    emitted in wrong section
           Product: gcc
           Version: 5.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rbd at debian dot org
  Target Milestone: ---

The example below is extracted via creduce from a large program I have.  The
program runs incorrectly when build with gcc 5.4.1 because one object file
contains a constructor (roughly) std::vector<...allocator>( allocator const& )
but also a symbol for std::vector<...allocator>( std::vector const& )that
points to the same function.  When the full program is run, a call to the
vector copy constructor ends up linked to the wrong function because the
dynamic linker happens to choose the symbol that really points to
std::vector<...allocator>( allocator const& ).  This makes code that should
copy a vector end up constructing an empty one instead using a bogus allocator.

I believe this small code shows the same failure:

$ cat b.cpp
template <typename, typename _Alloc> class vector {
public:
  vector();
  vector(const _Alloc &) {}
  void operator=(vector) { vector a(get_allocator()); }
  _Alloc get_allocator();
};

struct inherent;
template <typename, typename = inherent, typename = decltype(nullptr)>
struct allocator_affinity {};

typedef vector<void *, allocator_affinity<void *>> addr_list_t;

struct A {
  A(int) {}
  addr_list_t req_start_h_0;
  void req_start() { req_start_h_0 = addr_list_t(); }
};

int b;
void fn1() {
  A a(b);
  a.req_start();
}

$ g++-5 -v -std=c++11 -o b.o -c b.cpp
Using built-in specs.
COLLECT_GCC=g++-5
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 5.4.1-1'
--with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-5 --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 --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 5.4.1 20160803 (Debian 5.4.1-1) 
COLLECT_GCC_OPTIONS='-v' '-std=c++11' '-o' 'b.o' '-c' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/5/cc1plus -quiet -v -imultiarch x86_64-linux-gnu
-D_GNU_SOURCE b.cpp -quiet -dumpbase b.cpp -mtune=generic -march=x86-64
-auxbase-strip b.o -std=c++11 -version -o /tmp/ccmGdTt0.s
GNU C++11 (Debian 5.4.1-1) version 5.4.1 20160803 (x86_64-linux-gnu)
        compiled by GNU C version 5.4.1 20160803, GMP version 6.1.1, MPFR
version 3.1.4-p2, MPC version 1.0.3
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring duplicate directory "/usr/include/x86_64-linux-gnu/c++/5"
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/5/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/5
 /usr/include/x86_64-linux-gnu/c++/5
 /usr/include/c++/5/backward
 /usr/lib/gcc/x86_64-linux-gnu/5/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/5/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
GNU C++11 (Debian 5.4.1-1) version 5.4.1 20160803 (x86_64-linux-gnu)
        compiled by GNU C version 5.4.1 20160803, GMP version 6.1.1, MPFR
version 3.1.4-p2, MPC version 1.0.3
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: f5ac0328c94ad0bc615d4ccef0bcd937
COLLECT_GCC_OPTIONS='-v' '-std=c++11' '-o' 'b.o' '-c' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
 as -v --64 -o b.o /tmp/ccmGdTt0.s
GNU assembler version 2.26.1 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Debian) 2.26.1
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-std=c++11' '-o' 'b.o' '-c' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'

$ objdump -C -t b.o

b.o:     file format elf64-x86-64

SYMBOL TABLE:
0000000000000000 l    df *ABS*  0000000000000000 b.cpp
0000000000000000 l    d  .text  0000000000000000 .text
0000000000000000 l    d  .data  0000000000000000 .data
0000000000000000 l    d  .bss   0000000000000000 .bss
0000000000000000 l    d  .text._ZN1AC2Ei        0000000000000000
.text._ZN1AC2Ei
0000000000000000 l    d  .text._ZN1A9req_startEv        0000000000000000
.text._ZN1A9req_startEv
0000000000000000 l    d 
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEaSES4_ 0000000000000000
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEaSES4_
0000000000000000 l    d 
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_      
0000000000000000
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_
0000000000000000 l    d  .note.GNU-stack        0000000000000000
.note.GNU-stack
0000000000000000 l    d  .eh_frame      0000000000000000 .eh_frame
0000000000000000 l       .group 0000000000000000 A::A(int)
0000000000000000 l       .group 0000000000000000 vector<void*,
allocator_affinity<void*, inherent, decltype(nullptr)>
>::vector(allocator_affinity<void*, inherent, decltype(nullptr)> const&)
0000000000000000 l    d  .comment       0000000000000000 .comment
0000000000000000 l    d  .group 0000000000000000 .group
0000000000000000 l    d  .group 0000000000000000 .group
0000000000000000 l    d  .group 0000000000000000 .group
0000000000000000 l    d  .group 0000000000000000 .group
0000000000000000  w    F .text._ZN1AC2Ei        000000000000001e A::A(int)
0000000000000000         *UND*  0000000000000000 vector<void*,
allocator_affinity<void*, inherent, decltype(nullptr)> >::vector()
0000000000000000  w    F .text._ZN1AC2Ei        000000000000001e A::A(int)
0000000000000000  w    F .text._ZN1A9req_startEv        0000000000000035
A::req_start()
0000000000000000  w    F
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEaSES4_ 000000000000002e
vector<void*, allocator_affinity<void*, inherent, decltype(nullptr)>
>::operator=(vector<void*, allocator_affinity<void*, inherent,
decltype(nullptr)> >)
0000000000000000 g     O .bss   0000000000000004 b
0000000000000000 g     F .text  000000000000002b fn1()
0000000000000000         *UND*  0000000000000000 vector<void*,
allocator_affinity<void*, inherent, decltype(nullptr)> >::get_allocator()
0000000000000000  w    F
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_      
000000000000000f vector<void*, allocator_affinity<void*, inherent,
decltype(nullptr)> >::vector(allocator_affinity<void*, inherent,
decltype(nullptr)> const&)
0000000000000000  w    F
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEaSES4_ 000000000000002e
_ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEaSES5_
0000000000000000  w    F
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_      
000000000000000f vector<void*, allocator_affinity<void*, inherent,
decltype(nullptr)> >::vector(allocator_affinity<void*, inherent,
decltype(nullptr)> const&)
0000000000000000  w    F
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_      
000000000000000f vector<void*, allocator_affinity<void*, inherent,
decltype(nullptr)> >::vector(vector<void*, allocator_affinity<void*, inherent,
decltype(nullptr)> > const&)
0000000000000000  w    F
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_      
000000000000000f vector<void*, allocator_affinity<void*, inherent,
decltype(nullptr)> >::vector(vector<void*, allocator_affinity<void*, inherent,
decltype(nullptr)> > const&)

Notice that the last section,
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3 contains both
the constructors

    vector<void*, allocator_affinity<void*, inherent, decltype(nullptr)>
>::vector(allocator_affinity<void*, inherent, decltype(nullptr)> const&)
    vector<void*, allocator_affinity<void*, inherent, decltype(nullptr)>
>::vector(vector<void*, allocator_affinity<void*, inherent, decltype(nullptr)>
> const&)

pointing at the very same address.  I don't think there is any reason to create
the copy constructor at all - neither gcc 4.9 nor gcc 6.1 emit that symbol.

Also if I run "g++-5 -std=c++11 -o b.S -S b.cpp" to create assembly output, I
see

        .section       
.text._ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_,"axG",@progbits,_ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC5ERKS3_,comdat
        .align 2
        .weak   _ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_
        .type   _ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_,
@function
_ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_:
.LFB9:
        .cfi_startproc
        pushq   %rbp
        .cfi_def_cfa_offset 16
        .cfi_offset 6, -16
        movq    %rsp, %rbp
        .cfi_def_cfa_register 6
        movq    %rdi, -8(%rbp)
        movq    %rsi, -16(%rbp)
        nop
        popq    %rbp
        .cfi_def_cfa 7, 8
        ret
        .cfi_endproc
.LFE9:
        .size   _ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_,
.-_ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_
        .weak   _ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS4_
        .set   
_ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS4_,_ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_
        .weak   _ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC1ERKS3_
        .set   
_ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC1ERKS3_,_ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC2ERKS3_
        .weak   _ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC1ERKS4_
        .set   
_ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC1ERKS4_,_ZN6vectorIPv18allocator_affinityIS0_8inherentDnEEC1ERKS3_

so it seems the compiler is intentionally creating this strange alias...