[Vm-dev] [commit][3753] Do not use -O3 optimization, -O2 is safer and works well.

[David T. Lewis]

On Wed, Dec 21, 2016 at 10:11:39AM +0000, Jan Vrany wrote:
>  
> On Tue, 2016-12-20 at 21:54 -0500, David T. Lewis wrote:
> > ??
> > On Wed, Dec 21, 2016 at 10:40:32AM +0800, Ben Coman wrote:
> > > ??
> > > I'd be interested to know the reason sends get slower (if known).
> > > cheers -ben
> > 
> > No clue, I was just sanity checking to make sure that -O2 was not
> > horribly
> > worse. It was not. But I suspect all of this is likely to vary
> > depending on
> > gcc compiler version and phase of the moon.
> 
> This post:
> 
> http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html
> 
> explains the dependency on moon phases (and compiler versions) :-) 
> 

Thanks. Indeed there is probably some undefined C behavior in there, although
I was not able to spot it. If anyone is interested in lending their eyes to
the problem, I was able to localize the crash to intermittent segfaults that
occurred in OSProcessPlugin>>fixPointersInArrayOfStrings: which is generated
in C (for a V3 image, not Spur) as:

/*      Use the address offsets in offsetArray to fix up the pointers in cStringArray.
        The result is a C array of pointers to char, used for argv and env vectors. */

static sqInt fixPointersInArrayOfStringswithOffsetscount(char *flattenedArrayOfStrings, sqInt *offsetArray, sqInt count) {
    sqInt idx;
    char **ptr;

        ptr = ((char **) flattenedArrayOfStrings);
        idx = 0;
        while (idx < count) {
                ptr[idx] = (flattenedArrayOfStrings + (((offsetArray[idx]) >> 1)));
                idx += 1;
        }
        return null;
}