Re: [PATCH 2/2] x86/mtrr: fix build with gcc9

From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Charles Arnold <CARNOLD@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Wei Liu <wei.liu2@citrix.com>, Juergen Gross <jgross@suse.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH 2/2] x86/mtrr: fix build with gcc9
Date: Thu, 7 Mar 2019 11:55:54 +0100	[thread overview]
Message-ID: <20190307105554.42ek2lerz7nujfef@Air-de-Roger> (raw)
In-Reply-To: <5C80F32C020000780021C626@prv1-mh.provo.novell.com>

On Thu, Mar 07, 2019 at 03:32:12AM -0700, Jan Beulich wrote:
> generic.c: In function ‘print_mtrr_state’:
> generic.c:210:11: error: ‘%0*lx’ directive output between 1 and 1073741823 bytes may cause result to exceed
> ‘INT_MAX’ [-Werror=format-overflow=]
>   210 |    printk("%s  %u base %0*"PRIx64"000 mask %0*"PRIx64"000 %s\n",
>       |           ^~~~~~~~~~~~~~~~~
> generic.c:210:44: note: format string is defined here
>   210 |    printk("%s  %u base %0*"PRIx64"000 mask %0*"PRIx64"000 %s\n",
> generic.c:210:11: note: directive argument in the range [0, 4503599627370495]
>   210 |    printk("%s  %u base %0*"PRIx64"000 mask %0*"PRIx64"000 %s\n",
>       |           ^~~~~~~~~~~~~~~~~
> generic.c:210:11: note: assuming directive output of 1 byte
> 
> Restrict the width of the variable "width" controlling the number of
> address digits output.

I have to admit I'm not sure why gcc complains here, and why switching
to unsigned char fixes it. unsigned char max value would be 255, which
when used as a width to print an unsigned long it's also too high?

Does checking that width <= 16 also placate gcc?

Or maybe I'm just not understanding what gcc complains about.

Thanks.

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