Re: Re: pgsql: Convert contrib/seg's bool-returning SQL functions to V1 call co

On 2016-04-26 22:38:28 -0400, Noah Misch wrote:
> On Fri, Apr 22, 2016 at 03:54:48PM +0000, Tom Lane wrote:
> > Convert contrib/seg's bool-returning SQL functions to V1 call convention.
> >
> > It appears that we can no longer get away with using V0 call convention
> > for bool-returning functions in newer versions of MSVC.  The compiler
> > seems to generate code that doesn't clear the higher-order bits of the
> > result register, causing the bool result Datum to often read as "true"
> > when "false" was intended.  This is not very surprising, since the
> > function thinks it's returning a bool-width result but fmgr_oldstyle
> > assumes that V0 functions return "char *"; what's surprising is that
> > that hack worked for so long on so many platforms.
>
> Does this warrant a change to the "Section 2" comment of postgres.h,
> explaining that its precautions no longer suffice everywhere?

I don't understand why we don't just drop V0. It makes debugging harder,
exploitation easier (call arbitrary functions), and really has no
features making it desirable.

Andres