Subject: Re: [PATCH v2 2/3] ci: add build checking for side-effects in assert() calls

From: Taylor Blau <[email-masked]>
Date: Mon, 17 Mar 2025 18:30:53 -0400

On Sun, Mar 16, 2025 at 06:42:01AM +0000, Elijah Newren via GitGitGadget wrote:
> We have roughly 566 assert() calls in our codebase (my grep might have
> picked up things that aren't actually assert() calls, but most appeared
> to be).  All but 9 of them can be determined by gcc to be free of side
> effects with a clever redefine of assert() provided by Bruno De Fraine
> (from
> https://stackoverflow.com/questions/10593492/catching-assert-with-side-effects),
> who upon request has graciously placed his two-liner into the public
> domain without warranty of any kind.  The current 9 assert() calls
> flagged by this clever redefinition of assert() appear to me to be free
> of side effects as well, but are too complicated for a compiler/linker
> to figure that since each assertion involves some kind of function call.
> Add a CI job which will find and report these possibly problematic
> assertions, and have the job suggest to the user that they replace these
> with BUG_IF_NOT() calls.

Very nice, and thank you Bruno for placing your very clever assert() in
the public domain :-).

I wonder if it might be useful to explain this in
Documentation/CodingGuidelines as a follow-up to this series. I was
thinking of a scenario where someone either writes a side-effecting
assert(), or a non-side-effecting one that is too complicated to prove
otherwise.

If that person runs 'make test' locally, they might not see any
failures, but then be surprised when CI fails on the new step. It may be
worth mentioning that we have such a check, and that we expect all
assert() statements to be side effect-free, and that developers can
verify this by ci/check-unsafe-assertions.sh.

But that may bring us into an assert() versus BUG_IF_NOT() debate, which
may be somewhat counterproductive, so I'm just as happy if you did
nothing here :-).

Thanks,
Taylor