Re: [Dotgnu-libjit] Possible Libjit bug

[Klaus Treichel]

Hi Simone,

i think i know what the problem is.

The problematic value has been assigned to a global register.
In your libjittest_incorrect sample the value is used before a value was
assigned to the register (from the program order view and not the
program flow view).
So the in_global_register flag is still 0 even if it should be 1 at the
start of each block.

At the end of each block the values are spilled back to the global
registers anyways so this should be ok.

The change would be setting in_global_register = 1 where
has_global_register is set to 1 too (in _jit_regs_alloc_global).

Looks like this problem is not x86 specific.
 
@Aleksey: What do you think?

Cheers,
Klaus

Am Mittwoch, den 29.09.2010, 15:28 -0400 schrieb Simone Campanoni:
> Hi all,
>     I would like to show a possible bug of Libjit I have found in the
> attached examples.
> I am using Libjit from the git repository and the Intel x86 back-end.
> 
> The program libjittest_correct.c and libjittest_incorrect.c should have
> the same behavior and they should return zero as output.
> If you try to compile them, you will find an incorrect execution of
> libjittest_incorrect.c (it will return 1 instead of 0).
> 
> My guess is that the error is within the usage of global registers of
> x86 back-end.
> 
> I hope you will find this useful to improve the Libjit library.
> 
> Thanks for your work,
> Simone Campanoni
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