anonymous namespaces and possible linker trouble

[Gianni Mariani <gmariani at chaincast dot com>]

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