[PATCH v2] Initialize preloaded DSOs earlier [BZ #14379]

[Florian Weimer]

* Vincent Whitchurch:

> Currently, preloaded DSOs are initialized after linked-in DSOs.
>
> However, in many 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.
>
> So ensure that preloaded libraries are initialized as early as possible
> and finalized as late as possible.  Dependencies are still taken into
> account: DSOs which the preloaded DSO depends on are correctly
> initialized before it and finalized after it.
>
> If multiple DSOs are preloaded, DSOs earlier on the preload list will be
> initialized earlier and finalized later than DSOs present later on the
> list, analogous to how DSOs earlier on the preload list are searched for
> symbols before DSOs later on the preload list.
>
> Add a test case for this.
>
> Test suite run on x86-64.

Rich Felker shared this insightful comment:

  <https://sourceware.org/bugzilla/show_bug.cgi?id=14379#c9>

I'm no longer sure if the feature is a good idea after all (whether
applied to all LD_PRELOAD objects, or a subset of them using a new
environment variable).  Sorry.

Thanks,
Florian