Re: anonymous namespaces and possible linker trouble

[Gianni Mariani <gmariani at chaincast dot com>]

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