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

Hi,

d8f5acbdb9b made me wonder if we should add a compiler option to warn when
stack frames are large.  gcc compatible compilers have -Wstack-usage=limit, so
that's not hard.

Huge stack frames are somewhat dangerous, as they can defeat our stack-depth
checking logic. There are also some cases where large stack frames defeat
stack-protector logic by compilers/libc/os.

It's not always obvious how large the stack will be. Even if you look at all
the sizes of the variables defined in a function, inlining can increase that
substantially.

Here are all the cases a limit of 64k finds.


[1345/1940 42  69%] Compiling C object src/bin/pg_verifybackup/pg_verifybackup.p/pg_verifybackup.c.o
../../../../../home/andres/src/postgresql/src/bin/pg_verifybackup/pg_verifybackup.c: In function 'verify_file_checksum':
../../../../../home/andres/src/postgresql/src/bin/pg_verifybackup/pg_verifybackup.c:842:1: warning: stack usage is 131232 bytes [-Wstack-usage=]  842 | verify_file_checksum(verifier_context *context, manifest_file *m,      | ^~~~~~~~~~~~~~~~~~~~

This one's down to me. I asked Robert some time back why we were using a very conservative buffer size, and he agreed we could probably make it larger, but the number chosen is mine, not his. It was a completely arbitrary choice.

I'm happy to reduce it, but it's not clear to me why we care that much for a client binary. There's no stack depth checking going on here.

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com