[Bug lto/105877] New: GNU strip breaks -flto -g .o files

[Bug lto/105877] New: GNU strip breaks -flto -g .o files

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105877

            Bug ID: 105877
           Summary: GNU strip breaks -flto -g .o files
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
                CC: hjl.tools at gmail dot com, hubicka at gcc dot gnu.org,
                    marxin at gcc dot gnu.org
  Target Milestone: ---
              Host: x86_64-unknown-linux-gnu

Initially reported by drnfc on
https://github.com/trofi/nix-guix-gentoo/issues/19 where gcc failed to link
nix-2.9.0 against stripped liblowdown.a. Both are built with -flto.

I'm not sure if it's a strip bug, gcc bug or both. I think (did not check) it
used to work long ago. I'm leaning towards gcc bug and filing it here first.

Here is a minimal reproducer:

    // $ cat document.c
    void lowdown_doc_new(void) {}

    // $ cat markdown.cc
    extern "C" { void lowdown_doc_new(void); }
    int main(){ lowdown_doc_new(); }

    $ gcc -flto -g -c -o document.o document.c
    $ cp document.o document-stripped.o
    $ strip -g document-stripped.o
    $ g++ markdown.cc -o a document.o -flto-partition=max -flto -g
    $ g++ markdown.cc -o a document-stripped.o -flto-partition=max -flto -g
    ld: /tmp/ccajK6YG.ltrans0.ltrans.o:(.debug_info+0x2f): undefined reference
to `document.c.20ce96f1'

$ gcc -v |& unnix
Using built-in specs.
COLLECT_GCC=/<<NIX>>/gcc-13.0.0/bin/gcc
COLLECT_LTO_WRAPPER=/<<NIX>>/gcc-13.0.0/libexec/gcc/x86_64-unknown-linux-gnu/13.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with:
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.0.0 20220605 (experimental) (GCC)

[Bug lto/105877] GNU strip breaks -flto -g .o files

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105877

--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
"strip -g" removed .gnu.debuglto_.debug_info sections. Should LTO remove the
references of stripped debug info?  Or should "strip -g" keep LTO debug info?

[Bug lto/105877] GNU strip breaks -flto -g .o files

[hubicka at kam dot mff.cuni.cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105877

--- Comment #2 from hubicka at kam dot mff.cuni.cz ---
> "strip -g" removed .gnu.debuglto_.debug_info sections. Should LTO remove the
> references of stripped debug info?  Or should "strip -g" keep LTO debug info?

I suppose we should try to immitate what happens without -flto, so
probably check for the presence of debuglto sections and avoid producing
debug info when they have been stripped?
I am not sure how hard would be to implement this especially in
situations where part of object files were stripped and others not?

[Bug lto/105877] GNU strip breaks -flto -g .o files

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105877

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

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

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to hubicka from comment #2)
> > "strip -g" removed .gnu.debuglto_.debug_info sections. Should LTO remove the
> > references of stripped debug info?  Or should "strip -g" keep LTO debug info?
> 
> I suppose we should try to immitate what happens without -flto, so
> probably check for the presence of debuglto sections and avoid producing
> debug info when they have been stripped?
> I am not sure how hard would be to implement this especially in
> situations where part of object files were stripped and others not?

I think it might be possible to detect whether the compiled objects are
stripped and then avoid streaming references to its debug sections by
magically turning it to -g0.  But not sure how awkward this will be.

Not sure why strip now strips .gnu.debuglto_.debug_info, it didn't do that
before.

[Bug lto/105877] GNU strip breaks -flto -g .o files

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105877

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-06-16