I wrote:
> ... The simplest explanation
> I can think of is that it's *only* shmctl that is malfunctioning, not
> the other SysV shared memory calls. Which is even weirder, and
> definitely seems to move the problem into the category of kernel bug
> rather than configuration mistake.
Hmmm ... Google turned up the information that FreeBSD migrated from int
to size_t variables for shared memory size between 7.0 and 8.0, and in
particular that the size of the struct used by shmctl() changed in
8.0. So I'm now wondering if what you're dealing with is some sort of
version skew problem. Could it be that you built Postgres against
system header files that don't match your kernel version? I'm not
exactly sure how that would manifest as this particular signal,
but it seems worth checking.
regards, tom lane