[Bug c++/111788] New: g++ DWARF for void foo(...) missing unspecified parameters DIE

[Bug c++/111788] New: g++ DWARF for void foo(...) missing unspecified parameters DIE

[gprocida at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111788

            Bug ID: 111788
           Summary: g++ DWARF for void foo(...) missing unspecified
                    parameters DIE
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gprocida at google dot com
  Target Milestone: ---

I'm putting this in component c++ rather than debug, because the debug
information is correct for C compilation.

FWIW, clang++-15 does emit DW_TAG_unspecified_parameters.

$ cat v.c
int foo1(int x, int y, ...) { return x + y; }
int foo2(int x, ...) { return x; }
int foo3(...) { return 0; }

$ gcc -Wall -Wextra -g -c v.c v.o
# DWARF for foo3 includes DW_TAG_unspecified_parameters

$ g++ -Wall -Wextra -g -c v.c v.o
# DWARF for foo3 does NOT include DW_TAG_unspecified_parameters

$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/13/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 13.2.0-4'
--with-bugurl=file:///usr/share/doc/gcc-13/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-13
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/libexec --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-13-oyarai/gcc-13-13.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-13-oyarai/gcc-13-13.2.0/debian/tmp-gcn/usr
--enable-offload-defaulted --without-cuda-driver --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=28
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.2.0 (Debian 13.2.0-4)

[Bug c++/111788] g++ DWARF for void foo(...) missing unspecified parameters DIE

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111788

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-10-12
     Ever confirmed|0                           |1
      Known to fail|                            |4.1.2
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, does not look like a regression either.

[Bug c++/111788] g++ DWARF for void foo(...) missing unspecified parameters DIE

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111788

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
I wonder if foo (...) is a GNU extension (it was for C).

[Bug c++/111788] g++ DWARF for void foo(...) missing unspecified parameters DIE

[gprocida at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111788

--- Comment #3 from Giuliano Procida <gprocida at google dot com> ---
https://en.cppreference.com/w/cpp/language/variadic_arguments (see introduction
and Notes)

It's been allowed for longer than in C, but there is no portable way of
accessing the arguments.

[Bug c++/111788] g++ DWARF for void foo(...) missing unspecified parameters DIE

[gprocida at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111788

--- Comment #4 from Giuliano Procida <gprocida at google dot com> ---
Also worth noting that while Clang gives virtual table entries (for struct X)
this type in DWARF:

int(** _vptr.X)(...)

GCC gives them this type:

int(** _vptr$X)()

The different member names are an unfortunate inconsistency.

Clang is strictly better on the typing, stating that the virtual functions take
an unknown number of arguments. Perhaps even better would have been if the
first argument had been specified as type X*.

In any case, this is likely all cosmetic as debuggers have all the special
knowledge needed.