Re: [gentoo-user] ...if linking a completly unused library...

[Rich Freeman]

On Sun, Oct 2, 2016 at 9:54 AM, Michael Orlitzky <mjo@g.o> wrote:
> On 10/02/2016 01:18 AM, Meino.Cramer@×××.de wrote:
>>
>> One curious question remains:
>> If -as-needed is included, all libs will be "delinked" :), which
>> are not used...so I am throwing away stuff, which no code calls:
>> WHY should this cause trouble?
>> Or is it again oversimplified by me? :) ;) 8)
>>
>
> Suppose I write a program called "foo" and a library that it uses called
> "libfoo". If the libfoo library uses OpenSSL and the main executable has
> -lssl in its link command, everything will work fine by default. But, if
> you add --as-needed to your linker flags and don't specifically link
> libfoo against OpenSSL, the result will be underlinked.
>

Typically the problems that come up result from using a library
without explicitly linking it, assuming that it will be there because
something else will pull it in.  There may be niche situations where
problems are unavoidable, but for the most part it comes down to
always passing libraries to the linker if you use them.

In Gentoo lowering the number of unnecessary linked libraries is
highly desirable, because anytime one of those libraries changes its
SONAME any packages that use it must be rebuilt.  When you have a lot
of overlinking that greatly increases the amount of rebuilding you end
up with, and more circular dependency issues and such, etc.  This is
why --as-needed became the default (after a lot of build system
fixing).  Gentoo has a tendency to find bugs in build systems because
we run them in a variety of environments/etc.  Binary distros can
afford to just fuss with it until they somehow manage to get something
built, and then forget about it.  That said, some distros have better
tools for finding missing dependencies, like blocking access to files
that aren't part of a declared dependency during the build process.
I've looked at the portage jail and that actually wouldn't be hard to
add to Gentoo.  Right now portage configures the jail to give read
access to everything by default.  If you disabled that you could
instead pass a configuration that explicitly gives read access to
every single file in the build dependencies (and @system I suppose),
and denied everything else.  Implementation is left as an exercise to
the reader.

-- 
Rich