Re: [Tinycc-devel] bounds checking with tcc

[Herman ten Brugge]

I tried -b on windows for this simple code:
------
#include <stdio.h>

int
main (void)
{
  int i;
  int a[10];

  for (i = 0; i < 11; i++) {
    a[i] = i;
    printf ("%d %d\n", i, a[i]);
  }
  return 0;
}
---
It did not report an error as it should and printed wrong values. So 
windows is probably broken too.

Regards,

    Herman


On 2019-11-28 18:52, Christian Jullien wrote:
> Hello friends,
> First I must say that I never used tcc bound checking because, as Michael said, 
> I mostly use valgrind and other gcc/clang analysers when code security matters 
> in devel cycle.
> The only possible interesting use I see is when tcc is used natively on Windows 
> when no other C compiler is installed.
>
> I will not complain if this feature is removed.
>
> C.
>
> -----Original Message-----
> From: Tinycc-devel [mailto:tinycc-devel-bounces+eligis=address@hidden] On 
> Behalf Of Herman ten Brugge via Tinycc-devel
> Sent: Thursday, November 28, 2019 18:16
> To: Michael Matz
> Cc: Herman ten Brugge; Herman ten Brugge via Tinycc-devel
> Subject: Re: [Tinycc-devel] bounds checking with tcc
>
> 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
>
>
>
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