Re: RFC: Audit external function called indirectly via GOT

[Cary Coutant <ccoutant@gmail.com>]

>>> My suggestion was that the GOT entry could be statically initialized
>>> by the linker to point to the provisional PLT entry, rather than
>>> forcing the dynamic loader to go through all this messy computation.
>>> If auditing is not enabled, it would process the GLOB_DAT relocation
>>> normally, and set the GOT entry to point to the actual function,
>>> bypassing the provisional PLT and PLTGOT entries completely. If
>>> auditing is enabled, it could simply ignore the GLOB_DAT relocation
>>> (or, if the binary is PIE, it could process it as a RELATIVE
>>> relocation), and the -fno-plt calls will end up jumping to the
>>> provisional PLT entry.
>>>
>>> (This is already how we handle the PLTGOT entries: the linker
>>> statically initializes the entries to point to part (b)* of the PLT
>>> entry, while putting JUMP_SLOT relocations for those entries into the
>>> JMPREL table.)
>>>
>>> I think if you do that, none of these extra dynamic table entries will
>>> be needed, ...
>
> Your scheme is very similar to mine.   Both generate one GLOB_DAT
> and one JUMP_SLOT relocation for the same function symbol.  But
> only one of them should be used at run-time.  Your scheme may be
> simpler when LD_AUDIT is used since you don't need to update GOT
> slot.  But you still need to decide if a GLOB_DAT relocation should be
> skipped for LD_AUDIT.

That's why I then suggested this:

> I suppose you may also want to partition the GLOB_DAT relocations, so
> that the dynamic loader can easily figure out which ones to ignore
> when auditing is enabled. That would take another dynamic table entry.

-cary