What exactly does --enable-new-dtags do?

What exactly does --enable-new-dtags do?

[Mike Hearn]

Hi,

I would like to enable usage of DT_RUNPATH in my binaries, however the
only way to get this is with the --enable-new-dtags switch, the
exact effects of which are undocumented.

I don't mind DT_RUNPATH because support for this was added to glibc in
1999, which is old enough that I think most of my users have upgraded by
now. But I have no idea what else it does, so I have no idea how recent a
system will be required by using this switch.

It seems to me that a switch with such vague semantics is a bit dangerous.
Does anybody have a list of exactly what dyntags it enables? If not I'll
rummage about in the code and try to produce one.

thanks -mike

Re: What exactly does --enable-new-dtags do?

[Alan Modra]

On Sun, Apr 03, 2005 at 06:49:29PM +0100, Mike Hearn wrote:
> Hi,
> 
> I would like to enable usage of DT_RUNPATH in my binaries, however the
> only way to get this is with the --enable-new-dtags switch, the
> exact effects of which are undocumented.

The action of the switch itself is reasonably self-documenting.  What's
not so obvious is which of the new dtags ld generates, and which tags
ld.so recognises.  Documentation on the latter probably doesn't belong
in ld.texinfo.  Some info on the new tags can be found at
http://docsun.cites.uiuc.edu/sun_docs/C/solaris_9/SUNWdev/LLM/p55.html

> I don't mind DT_RUNPATH because support for this was added to glibc in
> 1999, which is old enough that I think most of my users have upgraded by
> now. But I have no idea what else it does, so I have no idea how recent a
> system will be required by using this switch.
> 
> It seems to me that a switch with such vague semantics is a bit dangerous.
> Does anybody have a list of exactly what dyntags it enables? If not I'll
> rummage about in the code and try to produce one.
> 
> thanks -mike
> 

-- 
Alan Modra
IBM OzLabs - Linux Technology Centre

Re: What exactly does --enable-new-dtags do?

[Mike Hearn]

On Mon, 2005-04-04 at 09:54 +0930, Alan Modra wrote:
> The action of the switch itself is reasonably self-documenting.  What's
> not so obvious is which of the new dtags ld generates, and which tags
> ld.so recognises.  Documentation on the latter probably doesn't belong
> in ld.texinfo.  Some info on the new tags can be found at
> http://docsun.cites.uiuc.edu/sun_docs/C/solaris_9/SUNWdev/LLM/p55.html

Right, that tells me the definition of DT_RUNPATH and DT_FLAGS, but I
already knew that from reading the ELF spec. What I don't know is
whether these two are the only ones --enable-new-dtags generates (I read
the original patch as well, but it may have changed since that time).

thanks -mike

Re: What exactly does --enable-new-dtags do?

[Alan Modra]

On Mon, Apr 04, 2005 at 11:00:16AM +0100, Mike Hearn wrote:
> Right, that tells me the definition of DT_RUNPATH and DT_FLAGS, but I
> already knew that from reading the ELF spec. What I don't know is
> whether these two are the only ones --enable-new-dtags generates

They are.

-- 
Alan Modra
IBM OzLabs - Linux Technology Centre

Re: What exactly does --enable-new-dtags do?

[Mike Hearn]

OK, thanks for your help. I'll enable it in my binaries then.

thanks -mike

On Mon, 2005-04-04 at 21:37 +0930, Alan Modra wrote:
> They are.