Re: [PATCH] nfp: remove h from printk format specifier

On Fri, 2020-12-25 at 14:13 -0800, Tom Rix wrote:

On 12/25/20 9:06 AM, Joe Perches wrote:

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On Fri, 2020-12-25 at 06:56 -0800, Tom Rix wrote:

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On 12/24/20 2:39 PM, Joe Perches wrote:

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Kernel code doesn't use a signed char or short with %hx or %hu very often
but in case you didn't already know, any signed char/short emitted with
anything like %hx or %hu needs to be left alone as sign extension occurs so:

Yes, this would also effect checkpatch.

Of course but checkpatch is stupid and doesn't know types
so it just assumes that the type argument is not signed.

In general, that's a reasonable but imperfect assumption.

coccinelle could probably do this properly as it's a much
better parser.  clang-tidy should be able to as well.

Ok.

But types not matching the format string is a larger problem.

Has there been an effort to clean these up ?

Not really no.  __printf already does a reasonable job for that.

The biggest issue for format type mismatches is the %p<foo> extensions.

__printf can only verify that the argument is a pointer, not
necessarily the 'right' type of pointed to object.

There are overflow possibilities like '"%*ph", len, pointer'
where pointer may not have len bytes available and, for instance,
mismatched uses of %pI4 and %pI6 where %pI4 expects a pointer to
4 bytes and %pI6 expects a pointer to 16 bytes.

Anyway it's not that easy a problem to analyze.