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Re: [Tinycc-devel] bounds checking with tcc

From: Christian Jullien
Subject: Re: [Tinycc-devel] bounds checking with tcc
Date: Thu, 28 Nov 2019 18:52:06 +0100

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.


-----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.



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