Re: Should we add a compiler warning for large stack frames?

Andres Freund <andres@anarazel.de> writes:
> On 2024-04-11 16:35:58 -0400, Tom Lane wrote:
>> Indeed.  I recall reading, not long ago, some Linux kernel docs to the
>> effect that automatic stack growth is triggered by a reference into
>> the page just below what is currently mapped as your stack, and
>> therefore allocating a stack frame greater than one page has the
>> potential to cause SIGSEGV rather than the desired stack extension.

> I think it's more than a single page, but I'm not entirely sure either. I
> think some compilers inject artificial stack accesses when extending the stack
> by a lot, but I don't remember the details.

Hmm.  You're right that I was misremembering the typical RAM page
size.  The kernel must be allowing stack frames bigger than 4K,
or we'd see problems everywhere.  I wonder how much bigger ...

> frame size      warnings
> 4096            155
> 8192            111
> 16384           36
> 32768           14
> 65536           8

> Suggests that starting somewhere around 16-32k might be reasonable?

I'm hesitant to touch more than a handful of places on the strength
of the info we've got; either it's wasted work or it's not enough
work, and we don't know which.  Might be time for some
experimentation.

            regards, tom lane