Re: [Tinycc-devel] Zeroing stack variables CValue

[Thomas Preudhomme]

Le 2014-03-27 07:23, Domingo Alvarez Duarte a écrit :
> Again my mistake, it does pass vla tests on linux 32 bits, the bounds
> check tests fail with garbage being passed to strlen.
> On arm it also works.

Hi Domingo,

I took a look at your patch and although I agree there is some 
problems, I find the approach a bit intrusive. For instance, in the vset 
case instead of zeroing the cval it would be better to fix the places 
that read the .ull field when it was initialized with vset. Normally a 
code would check the type before reading .ull and any caller of vset 
should do the right thing if the type needs to use the .ull field.

There is also get_tok_str that would require fixing as (as was pointed 
out by mobi phil) many caller of that function gives NULL as second 
parameter. It would be easily fixed with:

CValue cval;

if (!cv) {
    cval.ull = 0;
    cv = &cval;
}

The only place that should be fixed is when a variable is read but not 
initialized. When the wrong field of an union is read, either another 
field should be read or another field should have been set. Also, if tcc 
was used some day to compile on a big endian system the zeroing would 
also lead to garbage being read (only on little endian does it have no 
impact).

By the way, I'll try my best to take a look at your patch after the 
release. We'll then figure out how to best merge it. Maybe it's better 
in one big commit, I need to look at it first. I guess vtop, tok and tok 
are the biggest reason to have TCCState sneak in all function prototype, 
is that it?

Best regards,

Thomas