Re: [Valgrind-developers] Accessing function parameters

[Ivo R. <iv...@iv...>]

2016-09-08 15:05 GMT+02:00 Jakub Beránek <ber...@gm...>:

> I'm experimenting with writing a valgrind tool and I'd like to access
> function parameters, specifically the size given to malloc.
>

I assume you are implementing VG_(needs_malloc_replacement)() and have a
vgpreload_* module?


> It is passed to the malloc callback, but I need to know the address of the
> variable that was passed as the parameter (if it wasn't a constant).
>

Have a look at how existing tools implement VG_(needs_malloc_replacement)()
and in particular,
how do they implement pmalloc() callback. For example ms_malloc() in massif.

Passing of the function parameters from the client (instrumented program)
to the tool is performed as follows:
- vgpreload_* library is loaded with the client program
- vgpreload_* library defines malloc() replacements as per
vg_replace_malloc.c [for example via ALLOC_or_NULL]
- replacement function uses a client request: special sequence of
instructions [for example VALGRIND_NON_SIMD_CALL1]
- when Valgrind translates and instruments the client program and all the
libraries, it recognizes the client request and acts accordingly
- when the instrumented program is run, it calls into the tool's provided
callback [for example ms_malloc()]

Therefore there is no need to have any knowledge about function argument
passing convention,
which differs among architectures. This is all hidden behind client request
definition (valgrind.h)
and VEX frontend, specific to a particular architecture. The tool is
architecture agnostic.

Hope that helps,
I.

Btw, what is the main purpose of your tool?