anonymous namespaces and possible linker trouble

anonymous namespaces and possible linker trouble

[Gianni Mariani]

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

Re: anonymous namespaces and possible linker trouble

[Gianni Mariani]

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
>

Re: anonymous namespaces and possible linker trouble

[Gianni Mariani]

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
>>
>
>

Re: anonymous namespaces and possible linker trouble

[Joe Buck]

On Tue, Jan 07, 2003 at 05:21:14PM -0800, Gianni Mariani wrote:
> 
> Second repost:

Instead of nagging us into responding, please search Google for
"anonymous namespace", and read the first result that you find
(or click "I'm feeling lucky").  It will give you a mailing list
message; please click "Thread Index" and follow the whole thread.

Re: anonymous namespaces and possible linker trouble

[Gianni Mariani]

Joe Buck wrote:

>On Tue, Jan 07, 2003 at 05:21:14PM -0800, Gianni Mariani wrote:
>  
>
>>Second repost:
>>    
>>
>
>Instead of nagging us into responding, please search Google for
>"anonymous namespace", and read the first result that you find
>(or click "I'm feeling lucky").  It will give you a mailing list
>message; please click "Thread Index" and follow the whole thread.
>  
>
OK - my bad .... apologies etc etc ...

G