[Bug dynamic-link/30127] [rfe]: enable ld audit at run-time

["stsp at users dot sourceforge.net" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30127

--- Comment #19 from Stas Sergeev <stsp at users dot sourceforge.net> ---
(In reply to Jonathon Anderson from comment #18)
> void la_preinit(uintptr_t* cookie) {
>   void* h = dlmopen(LM_ID_BASE, NULL, RTLD_LAZY | RTLD_NOLOAD);
>   void (*hook)() = dlsym(h, "_auditor_hook");
>   hook(...);
> }

Well, yes, auditor_hook is a viable
solution perhaps in some cases. Though
in my case the auditor is brought in with
a solib plugin, not with the main application.
And currently DT_AUDIT is not supported for
solibs, see #30134.
And even if #30134 is fixed, will you be
able to resolve the auditor hook with
LM_ID_BASE if it is in an RTLD_LOCAL solib
rather than in a main executable?
I think not, so the scope of your solution
is quite limited.

> I'm a bit confused how the proposed interface would provide a better (or
> alternate) solution to the problem.

By doing
void *auditor_handle = dlload_audit_module("my_module", 0);
void (*auditor_cb)(void) = dlsym(auditor_handle, "auditor_control_interface");
Just as simple as that. :)

> Echoing a few of Florian's concerns, if
> you load an auditor after the application has been running for a time, you
> run a large risk of being passed an unrecognizable cookie (since the
> la_objopen callbacks are fired before the auditor is loaded).

Good point, so I'll adjust the patch to
not call the auditor for the lib for which
he missed the initial cookie... which doesn't
look simple. :)
Oh, will think...
Thanks!

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