---------- Forwarded message ----------
From: Jean-Claude Beaudoin <jean.claude.beaudoin@gmail.com>
Date: Wed, Mar 25, 2009 at 1:13 AM
Subject: CFFI should defend itself against fragile handling of narrow return types in SBCL on x86!
To: cffi-devel@common-lisp.net

Recent versions of GCC appear to be leaving spurious bits in the %eax register used to return the value of a C function on x86 based platforms when the return type is narrower than 32 bits (ie: short or char). SBCL does not defend itself against such register pollution and will return an incorrect value made up of those spurious bits in addition to the intended value. A partial fix for "signed" short and char has appeared in SBCL 1.0.25 but the "unsigned" cases are still vulnerable. I suggest that CFFI should defend itself against that dangerously permissive handling of narrow return types in SBCL through the use of a few filtering functions to be applied in those relevant cases, at least until SBCL fixes the issue for good.

Here is attached a patch against CFFI 0.10.4 with a version of the required code.

I also attach a set of test files that can be used to illustrate the problem.

Cheers,

Jean-Claude Beaudoin