Re: anonymous namespaces and possible linker trouble

[Gianni Mariani <gmariani at chaincast dot com>]

Second repost:

So if no-one is capable/willing to help, can anyone be kind enough to 
point me to the source files in gcc that are involved with creating the 
symbol names for anonymous namespaces so I can figure it out myself.  I 
promise I'll report what I find.

G

Gianni Mariani wrote:

> Repost:
>
> Can anyone comment ?
>
> I'm basically asking what are the possibilities of conflicts of the 
> same symbols in different anonymous namesspaces and compilation 
> units.  This was a problem I had seen in the past and I'd like to know 
> wether I may suffer this problem with gcc if I created a large number 
> of files with anonymous namespaces but with identical symbol names ?
>
> G
>
> Gianni Mariani wrote:
>
> > This is a question of how I could get into trouble.
> >
> > I've had problems in the past with anonymous namespaces and symbol 
> > clashes in the linker.  While the code below seems to link fine in 
> > the past (I don't remember which compiler) I had linker trouble on 
> > duplicate definitions of "int xx".
> >
> > How is this fixed in gcc now ? I notice that symbols are still global:
> >
> > .LFE1:
> > .Lfe1:
> >    .size   _Z1bi,.Lfe1-_Z1bi
> > .globl _ZN16_GLOBAL__N__Z1bi2xxE
> >    .bss
> >    .align 4
> >    .type   _ZN16_GLOBAL__N__Z1bi2xxE,@object
> >    .size   _ZN16_GLOBAL__N__Z1bi2xxE,4
> > _ZN16_GLOBAL__N__Z1bi2xxE:
> >    .zero   4
> >    .text
> >    .align 2
> >
> > So I'm thinking that some strange heristic is used to create a symbol 
> > name that will likely no clash - but that's not guarenteed.
> >
> > Why do symbols defined in anonymous namespaces need to have global 
> > linkage ?  Why can't they be defined using local linkage ?
> >
> > like:
> >    .local  xx
> >    .comm   xx,4,4
> >    .text
> >
> > G
> >
> > >>>> a.cpp
> >
> > void b( int a );
> >
> > namespace {
> > int             xx;
> > };
> >
> > void a( int a )
> > {
> >        b( xx );
> > }
> >
> > >>>>>>> b.cpp
> >
> > void a( int xx );
> >
> > void b( int a )
> > {
> > }
> >
> > namespace {
> > int                     xx;
> > };
> >
> > int main()
> > {
> >        a( xx );
> >        return 0;
> > }
> >
> > >>>>> Makefile
> >
> > xx : a.o b.o
> >        $(CXX) -o xx $^
> >
> > clean:
> >        rm *.o xx