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Re: [PATCH] lib/vsprintf.c: remove %Z support

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  Re: [PATCH] lib/vsprintf.c: remove %Z support Andrew Morton <akpm@linux-foundation.org> - 2017-01-06 01:40 +0100
    [PATCH] checkpatch.pl: warn against using %Z Alexey Dobriyan <adobriyan@gmail.com> - 2017-01-09 23:10 +0100
      Re: [PATCH] checkpatch.pl: warn against using %Z Joe Perches <joe@perches.com> - 2017-01-09 23:20 +0100

#1552427 — Re: [PATCH] lib/vsprintf.c: remove %Z support

On Wed, 4 Jan 2017 02:01:27 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:

> Now that %z is standartised in C99 there is no reason to support %Z.
> Unlike %L it doesn't even make format strings smaller.
> 
> Use BUILD_BUG_ON in a couple ATM drivers.
> 
> In case anyone didn't notice lib/vsprintf.o is about half of SLUB
> which is in my opinion is quite an achievement. Hopefully this patch
> inspires someone else to trim vsprintf.c more.

There's a risk that more %Z uses will sneak into the tree during the
4.10 development cycle, and possibly even later.  So I added a
note-to-self to re-grep the tree before sending this upstream, but that
won't prevent people adding new instances later on: code which was
tested under earlier kernels which has %Z support.

The best suggestion I have is to add a checkpatch rule to try to catch
new %Z's being added.

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#1554748 — [PATCH] checkpatch.pl: warn against using %Z

%Z is going to be removed in favour of %z.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 scripts/checkpatch.pl |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -5189,6 +5189,12 @@ sub process {
 				     "\%Ld/%Lu are not-standard C, use %lld/%llu\n" . $herecurr);
 				last;
 			}
+			# check for %Z
+			if ($string =~ /(?<!%)%[\*\d\.\$]*Z[diouxX]/) {
+				WARN("PRINTF_Z",
+				     "%Z is non-standard C, use %z\n" . $herecurr);
+				last;
+			}
 			if ($string =~ /0x%[\*\d\.\$\Llzth]*[udi]/) {
 				ERROR("PRINTF_0xDECIMAL",
 				      "Prefixing 0x with decimal output is defective\n" . $herecurr);

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#1554761 — Re: [PATCH] checkpatch.pl: warn against using %Z

On Tue, 2017-01-10 at 02:59 +0300, Alexey Dobriyan wrote:
> %Z is going to be removed in favour of %z.
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> ---
> 
>  scripts/checkpatch.pl |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -5189,6 +5189,12 @@ sub process {
>  				     "\%Ld/%Lu are not-standard C, use %lld/%llu\n" . $herecurr);
>  				last;
>  			}
> +			# check for %Z
> +			if ($string =~ /(?<!%)%[\*\d\.\$]*Z[diouxX]/) {
> +				WARN("PRINTF_Z",
> +				     "%Z is non-standard C, use %z\n" . $herecurr);
> +				last;
> +			}
>  			if ($string =~ /0x%[\*\d\.\$\Llzth]*[udi]/) {
>  				ERROR("PRINTF_0xDECIMAL",
>  				      "Prefixing 0x with decimal output is defective\n" . $herecurr);

Right concept, slightly incorrect implementation.

diouxX isn't necessary, ?<!% isn't necessary either as
there's a s/%%/__/g above it, last; probably isn't a
good idea as a single string could have both %Lu and
%Zu and unrelated, thanks for reminding me, I knew but
forgot to fix, the PRINTF_0xDECIMAL is defective as
there's a requirement that the match string only use
upper case.

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