Re: Extra import symbol in debug build

[Jonathan Wakely <jwakely.gcc@gmail.com>]

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On Fri, 17 Feb 2023, 11:32 , <i.nixman@autistici.org> wrote:

> On 2023-02-17 11:26, Jonathan Wakely wrote:
> > On Fri, 17 Feb 2023, 08:51 , <i.nixman@autistici.org> wrote:
> >
> >> On 2023-02-16 20:08, Jonathan Wakely wrote:
> >> > On Thu, 16 Feb 2023, 18:39 , <i.nixman@autistici.org> wrote:
> >> >
> >> >> On 2023-02-16 15:29, Jonathan Wakely wrote:
> >> >> > On Thu, 16 Feb 2023 at 15:25, i.nixman--- via Gcc-help
> >> >> > <gcc-help@gcc.gnu.org> wrote:
> >> >> >>
> >> >> >> hello,
> >> >> >>
> >> >> >>
> >> >> >> I can successfully build the same C++ code using GCC-8.3.1 for
> Debug
> >> >> >> (-g
> >> >> >> -O0) and Release (-g -O2) build.
> >> >> >> I can successfully debug the Release-executable on a remote host,
> but
> >> >> >> I
> >> >> >> can't debug the Debug-executable on a remote host, because the
> >> >> >> Debug-executable imports an extra symbol
> >> >> >> _ZNKSt9basic_iosIcSt11char_traitsIcEEcvbEv from libstdc++ which
> >> >> >> doesn't
> >> >> >> exist.
> >> >> >
> >> >> > It should exist, it has been there since GCC
> >> >>
> >> >> hmm...
> >> >>
> >> >> I just checked the two binaries using this cmd:
> >> >>
> >> >> > readelf -sW executable | grep
> >> >> > _ZNKSt9basic_iosIcSt11char_traitsIcEEcvbEv
> >> >>
> >> >> it shows nothing for release build, and shows this for debug build:
> >> >>
> >> >> >     54: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> >> >> > _ZNKSt9basic_iosIcSt11char_traitsIcEEcvbEv
> >> >> > 199898: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> >> >> > _ZNKSt9basic_iosIcSt11char_traitsIcEEcvbEv
> >> >>
> >> >
> >> >
> >> > This only shows that the function is inlined in the optimized build,
> >> > and
> >> > not in the debug build, so the debug one has an unresolved reference
> to
> >> > a
> >> > symbol defined in the libstdc++ dynamic library. This is completely
> >> > normal.
> >> >
> >>
> >> then I have two questions:
> >>
> >> 1. will the problem be solved by "pushing" a debug version of
> >> libstdc++
> >> on the remote machine?
> >>
> >
> > You don't need a debug version, the symbol is present in all builds of
> > libstdc++.
>
> hmm..
> but I can't confirm that using this cmd:
> readelf -sW /lib64/libstdc++.so.6 | grep
> _ZNKSt9basic_iosIcSt11char_traitsIcEEcvbEv
>

That suggests either you built it wrong, or that library is from an older
GCC, not the one you're compiling with.