On 2024-04-11 Th 15:01, Andres Freund wrote:
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
