[Bug d/104317] New: D language: rt.config module doesn't work as expected in GDC 9/10 (multiple definition linker error)

[Bug d/104317] New: D language: rt.config module doesn't work as expected in GDC 9/10 (multiple definition linker error)

[siarhei.siamashka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104317

            Bug ID: 104317
           Summary: D language: rt.config module doesn't work as expected
                    in GDC 9/10 (multiple definition linker error)
           Product: gcc
           Version: 10.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: siarhei.siamashka at gmail dot com
  Target Milestone: ---

The rt.config module provides a set of configuration variables with various
ways to override them as documented here:
   https://dlang.org/phobos/rt_config.html

The following small application can be used to test it:

    import std.stdio;
    extern(C) __gshared bool rt_cmdline_enabled = false;
    void main(string[] args) { writeln(args); }

== Expected correct result: ==

$ gdc test.d && ./a.out --DRT-this-cmdline-argument-should-not-be-filtered-out
["./a.out", "--DRT-this-cmdline-argument-should-not-be-filtered-out"]

== Got: ==

$ gdc-9.3.0 test.d
/usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0/../../../../x86_64-pc-linux-gnu/bin/ld:
/usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0/libgdruntime.a(lt8-config.o):/var/tmp/portage/sys-devel/gcc-9.3.0-r1/work/gcc-9.3.0/libphobos/libdruntime/rt/config.d:48:
multiple definition of `rt_cmdline_enabled'; /tmp/ccvDzGs7.o:(.bss+0x0): first
defined here
collect2: error: ld returned 1 exit status

$ gdc-12.0.1 test.d && ./a.out
--DRT-this-cmdline-argument-should-not-be-filtered-out
["./a.out", "--DRT-this-cmdline-argument-should-not-be-filtered-out"]

[Bug d/104317] D language: rt.config module doesn't work as expected in GDC 9/10 (multiple definition linker error)

[siarhei.siamashka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104317

--- Comment #1 from Siarhei Siamashka <siarhei.siamashka at gmail dot com> ---
An attempted fix for the linker error had been introduced in GDC11 via:
    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99914

But it made function templates non-inlineable as a side effect:
    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102765

Also cmdline arguments with "--DRT-" prefix are still incorrectly filtered out:

$ gdc-11.2.0 test.d && ./a.out
--DRT-this-cmdline-argument-should-not-be-filtered-out
["./a.out"]

It would be useful to have a better fix for this problem.

[Bug d/104317] D language: rt.config module doesn't work as expected in GDC 9/10 (multiple definition linker error)

[siarhei.siamashka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104317

Siarhei Siamashka <siarhei.siamashka at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |siarhei.siamashka at gmail dot com

--- Comment #2 from Siarhei Siamashka <siarhei.siamashka at gmail dot com> ---
Created attachment 52322
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52322&action=edit
proof of concept patch for gdc10

The attached proof of concept patch for GDC10 fixes the problem in a much less
invasive way. The idea is to just use weak attributes for global variables in
druntime instead of enclosing them in a "template {}" block.

A preliminary pull request for upstream druntime is tracked here:
https://github.com/dlang/druntime/pull/3716

The same simple fix also works fine for GDC11 if we undo PR99914:
https://gist.github.com/ssvb/d8a67fb445e96f9e66d0516a3ba62475

I first tried to toggle "flag_weak_templates" in "gcc/d/lang.opt" from 1 to 0
in GDC11 instead of reverting PR99914, but the resulting toolchain was unable
to compile and link even the most simple applications due to missing symbols
from Phobos.

The part preventing undesirable removal of cmdline arguments is cherry picked
from:
https://github.com/dlang/druntime/commit/ae9581c1e4b96de6707c71eb45dcc9c10dd4d402

[Bug d/104317] D language: rt.config module doesn't work as expected in GDC 9/10 (multiple definition linker error)

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104317

--- Comment #3 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
(In reply to Siarhei Siamashka from comment #2)
> I first tried to toggle "flag_weak_templates" in "gcc/d/lang.opt" from 1 to
> 0 in GDC11 instead of reverting PR99914, but the resulting toolchain was
> unable to compile and link even the most simple applications due to missing
> symbols from Phobos.
> 

r13-2002 (and r12-8673) is a start that sows the seeds to make the codegen
option -fno-weak-templates the default.  Should just be a case of extending the
forced emission to all instantiations too.