Re: [Tinycc-devel] bounds checking with tcc

[Herman ten Brugge]

On 2019-11-28 17:41, Michael Matz wrote:
> Hello again,
>
> but to maybe be a bit more constructive:
>
> On Thu, 28 Nov 2019, Michael Matz wrote:
>
> > > I fixed this with some push/pop trickery.
> I see, yeah, expanding calls during calls is broken as gfunc_call in the
> generators doesn't generally leave a trace in vtop[] which registers are
> currently holding values.  I think you only need so push/pop si/di, as
> cx/dx aren't used intentionally during reg-param setup.
>
> (I think i386-gen.c has a simila bug with fastcall functions).
I did this on purpose. The register calling usage is rdi, rsi, rdx, rcx.
So If a call uses four parameters the rdx, rcx would be overwritten
by the bounds checking code.
The bound_ptr_indirx calls overwrite rdi, rsi, rdx and rcx.
> > > This probably could be
> > > improved. I have now added a minimum patch so bounds checking works a
> > > little bit. We need still to fix the shared lib reloc problems and the
> > > malloc/free hooks.
> > Do we?  Can we perhaps also simply declare bounds checking to work only
> > with the main executable?  Or remove that whole feature altogether?
> And perhaps another compromise: only conditionally enable tracking of
> locals: Invent a new cmdline option (say, '-bb'), which sets
> do_bounds_checking to 2.  And only if it's > 1 you would also track
> locals, whereas with == 1 you would only track arrays and structs.
>
> Your decision, I think you can push this patch either with that change, or
> without (but try to remove cx/dx from the push/pop).  It doesn't make tccs
> source code larger or uglier in any meaningful way, but does fix practical
> bugs.
I can make a patch for this and as well.

Currently I think the best thing to do is to remove it. Other tools
do a much better job.

If you still want to keep the code we probably should add some warnings.
For example do not use it for shared libraries.

Regards,

    Herman