Re: pgsql: Revert online data checksum transitions

If we are pulling in stdbool.h and this is C11...that is undefined behavior
and because it wasn't validly initialized it is an indeterminate-value
read...which means for optimization that the compiler is within its right
to assume it is a 0 or 1 and could test it in different ways depending on
the surrounding code (nonzero test, compare to 1, etc).

On Wed, Sep 16, 2026 at 12:34 PM Jacob Champion <
jacob(dot)champion(at)enterprisedb(dot)com> wrote:

> On Wed, Sep 16, 2026 at 10:14 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > However, what I'm seeing as I trace through the crash on
> > longfin is that nulls[19] has a value that's not either 0 or 1 (not
> > too surprising), and somehow heap_compute_data_size is interpreting
> > that as "true" while fill_val is reading it as "false". According
> > to my understanding of the C standard, fill_val is in the wrong here.
>
> Is the _Bool representation allowed to contain anything but zero/false
> or one/true? I thought that was undefined behavior. (IIRC, mixing C++
> bool with our C89-era bool definition suffered from similar UB
> excitement.)
>
> --Jacob
>
>
>