Clarification on section variable attribute usage [try #2]

Clarification on section variable attribute usage [try #2]

[Franck Bui-Huu]

[ example updated ]

Hi,

Since at least 3.4, the GCC manual says:

     Use the `section' attribute with an _initialized_ definition of a
     _global_ variable, as shown in the example.  GCC issues a warning
     and otherwise ignores the `section' attribute in uninitialized
     variable declarations.

but this doesn't seem correct.

For example compiling the following tiny program:

	int foo __attribute__ ((__section__ (".init.data")));
	
	int main(int argc, char **argv)
	{
	        foo = 4;
	        return 0;
	}

produces no warning and the section attribute is not ignored at all:

	$ readelf -S a.out | grep -A1 init.data
	[24] .init.data        PROGBITS         000000000060080c  0000080c
	0000000000000004  0000000000000000  WA       0     0     4

This is with 4.1.2 from fedora, but I guess other GCC give the same result.

Could anybody clarify this point ?

Thanks,
		Franck

Re: Clarification on section variable attribute usage [try #2]

[Ian Lance Taylor]

Please never send a message to both gcc@gcc.gnu.org and
gcc-help@gcc.gnu.org.  Thanks.  I've dropped gcc@gcc.gnu.org from this
reply.

Franck Bui-Huu <vagabon.xyz@gmail.com> writes:

> Since at least 3.4, the GCC manual says:
> 
>      Use the `section' attribute with an _initialized_ definition of a
>      _global_ variable, as shown in the example.  GCC issues a warning
>      and otherwise ignores the `section' attribute in uninitialized
>      variable declarations.
> 
> but this doesn't seem correct.

Yes, I'm fairly sure that is no longer correct.  gcc is now smart
enough to not treat a variable with a section attribute as a common
variable.  I think the documentation is simply wrong.

Ian

Re: Clarification on section variable attribute usage [try #2]

[Franck Bui-Huu]

Hi Ian

Ian Lance Taylor wrote:
> Please never send a message to both gcc@gcc.gnu.org and
> gcc-help@gcc.gnu.org.  Thanks.
>

OK.

> Yes, I'm fairly sure that is no longer correct.  gcc is now smart
> enough to not treat a variable with a section attribute as a common
> variable.

Do you know when this happened ? Before GCC 3.2 ?

> I think the documentation is simply wrong.

It's probably high time to fix it up.

Thanks,
		Franck

Re: Clarification on section variable attribute usage [try #2]

[Ian Lance Taylor]

Franck Bui-Huu <vagabon.xyz@gmail.com> writes:

> > Yes, I'm fairly sure that is no longer correct.  gcc is now smart
> > enough to not treat a variable with a section attribute as a common
> > variable.
> 
> Do you know when this happened ? Before GCC 3.2 ?

I don't know when it happened, no.

> > I think the documentation is simply wrong.
> 
> It's probably high time to fix it up.

Yep.

Ian