Re: Concurrency has landed

[Paul Eggert]

On 12/21/2016 08:52 PM, Daniel Colascione wrote:
> > reasons, but also because the byte stack implementation relies on
> > using pointers to freed storage, which violates the C
> How?

If memory serves, the code has several pointers p, q, r, ... into a 
memory region based at b that it wants to move. It then does the 
equivalent of 'b1 = realloc (b, newsize); p += b1-b; q += b1-b; r += 
b1-b; ...; b = b1;'. The C standard does not allow this: a program is 
not allowed to look at a pointer to freed storage (even if it does not 
dereference the pointer), which means the expression 'b1-b' has 
undefined behavior.

Possibly my memory is wrong and realloc was not involved. Regardless, 
the code in question does not work with -fcheck-pointer-bounds, and it's 
confusing to rely on pointers to freed storage, even if you don't 
dereference them and the code happens to work. Also, the byte stack 
isn't needed so we might as well remove it.