Re: Why are we linking with --as-needed?

[Jeff Morriss <jeff.morriss.ws () gmail com>]

On 01/21/2016 10:17 PM, Guy Harris wrote:
> The GNU linker documentation says of the --as-needed flag
>
> --as-needed
> --no-as-needed
>         This option affects ELF DT_NEEDED tags for dynamic libraries mentioned on the command line after the 
> --as-needed option. Normally the linker will add a DT_NEEDED tag for each dynamic library mentioned on the command 
> line, regardless of whether the library is actually needed or not.  --as-needed causes a DT_NEEDED tag to only be 
> emitted for a library that at that point in the link satisfies a non-weak undefined symbol reference from a regular 
> object file or, if the library is not found in the DT_NEEDED lists of other needed libraries, a non-weak undefined 
> symbol reference from another needed dynamic library. Object files or libraries appearing on the command line after the 
> library in question do not affect whether the library is seen as needed. This is similar to the rules for extraction of 
> object files from archives.  --no-as-needed restores the default behaviour.
>
> --as-needed was added in this change:
>
>         commit b6cffe405019da8259413cfcb829339712a098a7
>         Author: Jörg Mayer <jmayer () loplof de>
>         Date:   Fri Aug 7 18:49:24 2009 +0000
>
>             - Add an AC macro to test linker flags.
>             - Test whether the linker supports --as-needed and if so,
>               adds it to LDFLAGS
>
> About all I could find for a reason were bugs such as
>
>         https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=1677
>
> complaining that Wireshark didn't build with --as-needed.
>
> So why is it useful that it be built - or, at least, buildable - with --as-needed?  (It's obviously not *necessary* as 
> not all platform support that capability.)

I thought I remembered seeing (back around the time of bug 1677) a web 
page explaining why it was a Good Idea.  About all I can find at the 
moment is this one:

https://wiki.gentoo.org/wiki/Project:Quality_Assurance/As-needed


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