Re: Support for automatic linking via pragma

["H.J. Lu" <hjl.tools@gmail.com>]

On Fri, Mar 4, 2011 at 8:52 AM, Ian Lance Taylor <iant@google.com> wrote:
> "H.J. Lu" <hjl.tools@gmail.com> writes:
>
>> On Fri, Mar 4, 2011 at 8:29 AM, Olaf van der Spek <olafvdspek@gmail.com> wrote:
>>> On Mon, Feb 28, 2011 at 7:17 PM, Olaf van der Spek <olafvdspek@gmail.com> wrote:
>>>> Hi,
>>>>
>>>> I've submitted a feature request for automatic linking via pragma:
>>>> http://sourceware.org/bugzilla/show_bug.cgi?id=12485
>>>> What do others think about the idea?
>>>
>>> Somebody?
>>>
>>> Let me quote the request:
>>> MSVC supports the following pragma, which can be used to automatically link a
>>> library when a header file is included. This is used by for example Boost.
>>>
>>> It makes linking with the right lib a lot simpler. No more fiddling
>>> with autoconf to detect the right lib name.
>>>
>>
>> Not necessarily.  Unlike DSO, object files don't have ABI/API
>> information. You may not link foo.o compiled with glibc 2.5/libbar
>> 1.3 against glibc 2.13/libbar 1.9
>
> I don't see how that is relevant to what Olaf is talking about.
>
> What Olaf is saying is that he wants to be able to have a .h file
> automatically a -l option to the link command line.

Don't you need to store such information in object files?

> What you are saying is that if that you have a .o file, you have to link
> against the -l which corresponds to the .h file which was used when the
> .o file was compiled.  That is of course a real problem, but it's a
> problem that exists whether or not we implement the MSVC pragma.
>

There is no such problem for DSO since we can encode ABI/API
info in DSO.

-- 
H.J.