From: Bill Wendling

Sent: 09 June 2022 23:49

On Thu, Jun 9, 2022 at 3:25 PM Andrew Morton [off-list ref] wrote:

quoted

On Thu,  9 Jun 2022 22:16:19 +0000 Bill Wendling [off-list ref] wrote:

quoted

This patch set fixes some clang warnings when -Wformat is enabled.

tldr:

-       printk(msg);
+       printk("%s", msg);

the only reason to make this change is where `msg' could contain a `%'.
Generally, it came from userspace.

It helps kernel developers not accidentally to insert an unescaped '%'
in their messages, potentially exposing their code to an attack
vector.

quoted

Otherwise these changes are a
useless consumer of runtime resources.

Calling a "printf" style function is already insanely expensive. :-) I
understand that it's not okay blithely to increase runtime resources
simply because it's already slow, but in this case it's worthwhile.

Yep, IMHO definitely should be fixed.
It is even possible that using "%s" is faster because the printf
code doesn't have to scan the string for format effectors.

quoted

I think it would be better to quieten clang in some fashion.

The "printk" and similar functions all have the "__printf" attribute.
I don't know of a modification to that attribute which can turn off
this type of check.

And you wouldn't want to for these cases.

The only problems arise when the format is calculated
(or passed in from a caller).
But that is likely to be dangerous - reading formats from
files (eg for language translation) isn't a good idea at all.

	David

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