[jit] Eliminate fixed-size buffers used with vsnprintf

[Joseph S. Myers]

On Wed, 24 Sep 2014, David Malcolm wrote:

> The ideal I'm aiming for here is that a well-behaved library should
> never abort, so I've rewritten these functions to use vasprintf, and
> added error-handling checks to cover the case where malloc returns NULL
> within vasprintf.

GCC is designed on the basis of aborting on allocation failures - as is 
GMP, which allows custom allocation functions to be specified but still 
requires them to exit the program rather than return, longjmp or throw an 
exception.

> I believe this fixes the specific issues you pointed out (apart from the
> numerous missing API comments, which I'll do it a followup).  Note that
> there's still a fixed-size buffer within gcc::jit::recording::context,
> the field:
> 
>   char m_first_error_str[1024];
> 
> Currently this is populated using strncpy followed by an explicit write
> of a truncation byte to make sure, but it *is* another truncation.
> 
> Presumably I should address this in a followup, by making that be
> dynamically-allocated?

Yes.  Arbitrary limits should be avoided in GNU.

-- 
Joseph S. Myers
joseph@codesourcery.com