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April 02, 2009
Link Problem
Hi All,

Someone has reported the issue here
(http://d.puremagic.com/issues/show_bug.cgi?id=1508)

Someone pointed, that the problem can be solved by changing the order of
object files. And this issue has been fixed in dmd.

I have the same problem by linking an executable using gdc.
Because my project cannot migrate to dmd immediately. 
So I want to change the order of object files. 
I have tried serveral combinations. But not get it done. (I have 380 object
files)

Can someone explain, what kind of a problem with compiler is this
specificly?


Best regards
--Qian
April 02, 2009
Re: Link Problem
在 Thu, 02 Apr 2009 19:16:10 +0800,Qian Xu <quian.xu@stud.tu-ilmenau.de>  
写道:

> Hi All,
>
> Someone has reported the issue here
> (http://d.puremagic.com/issues/show_bug.cgi?id=1508)
>
> Someone pointed, that the problem can be solved by changing the order of
> object files. And this issue has been fixed in dmd.
>
> I have the same problem by linking an executable using gdc.
> Because my project cannot migrate to dmd immediately.
> So I want to change the order of object files.
> I have tried serveral combinations. But not get it done. (I have 380  
> object
> files)
>
> Can someone explain, what kind of a problem with compiler is this
> specificly?
>
>
> Best regards
> --Qian
>
>

You're sure that's a linking problem?
GDC only use DMD frontend, so if it's a linking problem it should be ld's.

LD seems to behave absurdly that it expects to resolve symbols.
e.g.
a.o provides symbol c, and b.o needs symbol c
you'd better feed ld with: b.o a.o not a.o b.o

Though you have that amount of files, the effort of tweaking orders just  
wastes your time. Try to make your code dmd compatible and try dmd!
April 02, 2009
Re: Link Problem
davidl wrote:
> ...
> 
> Though you have that amount of files, the effort of tweaking orders just
> wastes your time. Try to make your code dmd compatible and try dmd!

I believe DMD on linux uses gcc (and by extension, ld) to link object files.

 -- Daniel
April 02, 2009
Re: Link Problem
davidl wrote:

> You're sure that's a linking problem?
> GDC only use DMD frontend, so if it's a linking problem it should be ld's.
> 
> LD seems to behave absurdly that it expects to resolve symbols.
> e.g.
> a.o provides symbol c, and b.o needs symbol c
> you'd better feed ld with: b.o a.o not a.o b.o
> 

If I change the order of the object files, I might see different error
messages. But all of them are about "undefined reference to ..."


> Though you have that amount of files, the effort of tweaking orders just
> wastes your time. Try to make your code dmd compatible and try dmd!

We are migrating. But it takes time :)
April 02, 2009
Re: Link Problem
davidl Wrote:

[...]
> You're sure that's a linking problem?
> GDC only use DMD frontend, so if it's a linking problem it should be ld's.
> 
> LD seems to behave absurdly that it expects to resolve symbols.
> e.g.
> a.o provides symbol c, and b.o needs symbol c
> you'd better feed ld with: b.o a.o not a.o b.o

dmd also uses gcc (and hence ld) as linker, so if it is an ld
problem, it'll stay. The behavior you mention above is only
true for library files, AFAIK, not for objects. You should have
all objects before the libraries, though.

Ciao
TomD
April 02, 2009
Re: Link Problem
On 2009-04-02 14:52:40 +0200, TomD <t_demmer@nospam.web.de> said:

> davidl Wrote:
> 
> [...]
>> You're sure that's a linking problem?
>> GDC only use DMD frontend, so if it's a linking problem it should be ld's.
>> 
>> LD seems to behave absurdly that it expects to resolve symbols.
>> e.g.
>> a.o provides symbol c, and b.o needs symbol c
>> you'd better feed ld with: b.o a.o not a.o b.o
> 
> dmd also uses gcc (and hence ld) as linker, so if it is an ld
> problem, it'll stay. The behavior you mention above is only
> true for library files, AFAIK, not for objects. You should have
> all objects before the libraries, though.
> 
> Ciao
> TomD

simply put ld scans for symbols in libraries in the order they appear, 
if liba uases symbolsy from libb you should like them as -L-la -L-lb.
Normally it is not difficult to achieve this, but as workaround you dan 
also tell the linker to recursively search also in the previous 
libraries, this slows the linking, but will allow any order in the 
libraries, even circular dependencies (that you would otherwise need to 
break liking libraries more than once).

Simply pass --start-group *all the libs* --end-group to the linker 
(i.e. -L--start-group to the compiler)
and (if your problem really came from this) it will go away

Fawzi
April 02, 2009
Re: Link Problem
Fawzi Mohamed wrote:
> 
> simply put ld scans for symbols in libraries in the order they appear,
> if liba uases symbolsy from libb you should like them as -L-la -L-lb.
> Normally it is not difficult to achieve this, but as workaround you dan
> also tell the linker to recursively search also in the previous
> libraries, this slows the linking, but will allow any order in the
> libraries, even circular dependencies (that you would otherwise need to
> break liking libraries more than once).
> 
> Simply pass --start-group *all the libs* --end-group to the linker
> (i.e. -L--start-group to the compiler)
> and (if your problem really came from this) it will go away
> 


I tried the following command
"gdc  -Wl,--start-group  Foo.o Foo2.o Bar/Foo3.o Bar/Foo4.o  -Wl,--end-group 
-o main -Ltango/lib -lgtango"

But it still does not work. The same problem.

The following is a dump of the actual error message

----------------------
build_trunk_build_1926/build_componenttest.out-`.text._D5tango4util10collection4impl16AbstractIterator80__T16AbstractIteratorTC9timetable6common3src10controller6entity7Vehicle7VehicleZ16AbstractIterator9remainingMFZk'
referenced in section
`.text.__t24__D5tango4util10collection4impl16AbstractIterator80__T16AbstractIteratorTC9timetable6common3src10controller6entity7Vehicle7VehicleZ16AbstractIterator9remainingMFZk[__t24__D5tango4util10collection4impl16AbstractIterator80__T16AbstractIteratorTC9timetable6common3src10controller6entity7Vehicle7VehicleZ16AbstractIterator9remainingMFZk]'
of
build/boost/timetable/common/src/controller/importer/ImportVehicleController_1.o:
defined in discarded section
`.text._D5tango4util10collection4impl16AbstractIterator80__T16AbstractIteratorTC9timetable6common3src10controller6entity7Vehicle7VehicleZ16AbstractIterator9remainingMFZk[_D5tango4util10collection4impl16AbstractIterator80__T16AbstractIteratorTC9timetable6common3src10controller6entity7Vehicle7VehicleZ16AbstractIterator9remainingMFZk]'
of
build/boost/timetable/common/src/controller/importer/ImportVehicleController_1.o
build_trunk_build_1926/build_componenttest.out:collect2: ld returned 1 exit
status
----------------------
April 02, 2009
Re: Link Problem
Qian Xu Wrote:

[...]
> I tried the following command
> "gdc  -Wl,--start-group  Foo.o Foo2.o Bar/Foo3.o Bar/Foo4.o  -Wl,--end-group 
> -o main -Ltango/lib -lgtango"
> 
> But it still does not work. The same problem.
> 
> The following is a dump of the actual error message
> 
> ----------------------
> build_trunk_build_1926/build_componenttest.out-`.text._D5tango4util10collection4impl16AbstractIterator80__T16AbstractIteratorTC9timetable6common3src10controller6entity7Vehicle7VehicleZ16AbstractIterator9remainingMFZk'
> referenced in section
> `.text.__t24__D5tango4util10collection4impl16AbstractIterator80__T16AbstractIteratorTC9timetable6common3src10controller6entity7Vehicle7VehicleZ16AbstractIterator9remainingMFZk[__t24__D5tango4util10collection4impl16AbstractIterator80__T16AbstractIteratorTC9timetable6common3src10controller6entity7Vehicle7VehicleZ16AbstractIterator9remainingMFZk]'
> of
> build/boost/timetable/common/src/controller/importer/ImportVehicleController_1.o:
> defined in discarded section
> `.text._D5tango4util10collection4impl16AbstractIterator80__T16AbstractIteratorTC9timetable6common3src10controller6entity7Vehicle7VehicleZ16AbstractIterator9remainingMFZk[_D5tango4util10collection4impl16AbstractIterator80__T16AbstractIteratorTC9timetable6common3src10controller6entity7Vehicle7VehicleZ16AbstractIterator9remainingMFZk]'
> of
> build/boost/timetable/common/src/controller/importer/ImportVehicleController_1.o
> build_trunk_build_1926/build_componenttest.out:collect2: ld returned 1 exit
> status
> ----------------------
As far as I can say from the error, ld discards a section. I just cannot
understand why. 

The info file of ld says:

***
3.6.7 Output Section Discarding
-------------------------------

The linker will not create output sections with no contents.  This is
for convenience when referring to input sections that may or may not be
present in any of the input files.  For example:
    .foo : { *(.foo) }
  will only create a `.foo' section in the output file if there is a
`.foo' section in at least one input file, and if the input sections
are not all empty.  Other link script directives that allocate space in
an output section will also create the output section.
****
Somehow, section ._D5tango4util10collection4impl16AbstractIterator80
(tango.util.collection.impl.AbstractIterator timetable.commonSource...)
get discarded.

Is there anything weird with this thing, e.g. inlined but referenced
in an external modulue? Can you rebuild all without optimization?

Ciao
TomD
(PS: Thanks to Fawzi, I did not know the grouping command
of ld)
April 03, 2009
Re: Link Problem
TomD wrote:

> As far as I can say from the error, ld discards a section. I just cannot
> understand why.
> 


If my project is compiled with "--debug" flag, and then there is no
link-problem.
April 03, 2009
Re: Link Problem
After a couple of miniutes googling around this seems
to be a bug in ld. Some aritlcles from 2007 or so 
recommend to downgrade to binutils 2.15 from 2.16.
*If* your installed binutils is 2.16, you may give it a try.

Ciao
Tom
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