Re: [PATCH] Add LD_PRELOAD_INIT_EARLY [BZ #14379]

[Vincent Whitchurch <vincent dot whitchurch at axis dot com>]

On Fri, Feb 15, 2019 at 12:43:54PM +0100, Florian Weimer wrote:
> * Vincent Whitchurch:
> > Currently, DSOs preloaded with LD_PRELOAD are initialized after
> > linked-in DSOs, unless dependencies require otherwise.
> >
> > However, in some cases it is desirable that preloaded DSO are
> > initialized before linked-in DSOs (unless dependencies require
> > otherwise).  For example, when malloc is overloaded using a preloaded
> > DSO for the purpose of heap profiling, we ideally want the preloaded DSO
> > to be initialized before other DSOs so that it has a chance to set up
> > its accounting code before their initializers are called.
> >
> > Changing the default behaviour could lead to breakage, so add a new
> > environment variable, LD_PRELOAD_INIT_EARLY, the presence of which will
> > ask preloaded libraries to be initialized as early as possible and
> > finalized as late as possible.  If multiple DSOs are preloaded, DSOs
> > earlier on the LD_PRELOAD list will be initalized earlier and finalized
> > later than DSOs present later on the list.
> >
> > Note that dependencies are still taken into account: DSOs which the
> > preloaded DSO depends on are correctly initalized before it and
> > finalized after it.
> 
> Maybe we should LD_PRELOAD to use this behavior instead?  Isn't that
> what users expect?

It's certainly what I personally expect, but I feared that someone may
actually be depending on the current behaviour, hence the new variable.
But I can certainly just change LD_PRELOAD's default behaviour if you
think that there is no risk for that.