linux-kernel - Re: [PATCH v2] wusb: use correct format characters

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Date:   Thu, 28 Feb 2019 13:53:31 -0800
From:   Joe Perches <joe@...ches.com>
To:     Louis Taylor <louis@...gniz.eu>, gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com, ndesaulniers@...gle.com,
        jflat@...omium.org
Subject: Re: [PATCH v2] wusb: use correct format characters

On Thu, 2019-02-28 at 12:24 +0000, Louis Taylor wrote:
> When compiling with -Wformat, clang warns:
> ./include/linux/usb/wusb.h:245:5: warning: format specifies type
> 'unsigned short' but the argument has type 'u8' (aka 'unsigned char')
> [-Wformat]
>   ckhdid->data[0],  ckhdid->data[1],
>   ^~~~~~~~~~~~~~~

I think the message is somewhat misguided as all the
vararg arguments have implicit integer promotions.

> ckhdid->data is unconditionally defined as `u8 data[16]`, so this patch
> updates the format characters to the correct one for unsigned char types.
[]
> diff --git a/include/linux/usb/wusb.h b/include/linux/usb/wusb.h
[]
> @@ -240,8 +240,8 @@ static inline size_t ckhdid_printf(char *pr_ckhdid, size_t size,
>  				   const struct wusb_ckhdid *ckhdid)
>  {
>  	return scnprintf(pr_ckhdid, size,
> -			 "%02hx %02hx %02hx %02hx %02hx %02hx %02hx %02hx "
> -			 "%02hx %02hx %02hx %02hx %02hx %02hx %02hx %02hx",
> +			 "%02hhx %02hhx %02hhx %02hhx %02hhx %02hhx %02hhx %02hhx "
> +			 "%02hhx %02hhx %02hhx %02hhx %02hhx %02hhx %02hhx %02hhx",
>  			 ckhdid->data[0],  ckhdid->data[1],
>  			 ckhdid->data[2],  ckhdid->data[3],
>  			 ckhdid->data[4],  ckhdid->data[5],

Better to use the vsprintf %ph extension insead.
---
 include/linux/usb/wusb.h | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/include/linux/usb/wusb.h b/include/linux/usb/wusb.h
index 9e4a3213f2c2..8c39ddf62951 100644
--- a/include/linux/usb/wusb.h
+++ b/include/linux/usb/wusb.h
@@ -239,17 +239,7 @@ enum {
 static inline size_t ckhdid_printf(char *pr_ckhdid, size_t size,
 				   const struct wusb_ckhdid *ckhdid)
 {
-	return scnprintf(pr_ckhdid, size,
-			 "%02hx %02hx %02hx %02hx %02hx %02hx %02hx %02hx "
-			 "%02hx %02hx %02hx %02hx %02hx %02hx %02hx %02hx",
-			 ckhdid->data[0],  ckhdid->data[1],
-			 ckhdid->data[2],  ckhdid->data[3],
-			 ckhdid->data[4],  ckhdid->data[5],
-			 ckhdid->data[6],  ckhdid->data[7],
-			 ckhdid->data[8],  ckhdid->data[9],
-			 ckhdid->data[10], ckhdid->data[11],
-			 ckhdid->data[12], ckhdid->data[13],
-			 ckhdid->data[14], ckhdid->data[15]);
+	return scnprintf(pr_ckhdid, size, "%16ph", ckhdid->data);
 }
 
 /*