Re: [RFC PATCH] Allow annotating calloc for Valgrind

[Alexander Monakov <amonakov@ispras.ru>]

On Thu, 29 Jun 2017, Rich Felker wrote:
> It reached the point of an faq item on irc; perhaps it was never
> discussed on the ml.

I feel a quick reminder of what was discussed would be very nice.

> If that happens, it's just a valgrind bug. It can see the memory was
> returned by calloc and therefore the contents are defined. But maybe
> before discussing this further we need to clarify what the actual
> scenario is.

Alright. As far as I can tell, everyone hits this (only) with static
linking. Valgrind core *does* have a concept of a symbol table being
distinct from dynamic symbol table (info from symtab is successfully
used for backtracing for example), so in principle Memcheck could use
just the .symtab when running unstripped static executables.

Unfortunately, historically the implementation of Memcheck relies
entirely on dynamic linking to intercept allocation functions. As a
result, Memcheck's functionality on static executables degrades
significantly (it can still find a subset of uninit access errors).

I guess the proper fix - wiring up .symtab-based interception - might
require more time than anyone was prepared to volunteer.

I think at the moment client requests are the only straightforward way
to use Memcheck fully with statically-linked programs.  But for full
functionality, people would need extra requests informing Memcheck
about the effects of static malloc & free. Where would such a patch
belong?

Alexander