linux-kernel - Re: %pa format specifier issues

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Date:	Tue, 05 Mar 2013 18:19:54 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	Stepan Moskovchenko <stepanm@...eaurora.org>,
	Rob Landley <rob@...dley.net>,
	George Spelvin <linux@...izon.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Andrei Emeltchenko <andrei.emeltchenko@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: %pa format specifier issues

On 03/05/13 17:18, Dave Hansen wrote:
> I went to go use the shiny new %pa specifier:
>
> void test_printk_pa(void)
> {
>         phys_addr_t p = 0x1234;
>         printk("p: %pa\n", p);
> }
>
> but gcc is spewing out warnings at me:
>
>> arch/x86/mm/physaddr.c: In function ‘test_printk_pa’:
>> arch/x86/mm/physaddr.c:95:2: warning: format ‘%p’ expects argument of type ‘void *’, but argument 2 has type ‘phys_addr_t’ [-Wformat]
> I assume that's because gcc doesn't know about '%pa', and just assumes
> it's a plain '%p'.  Should we be turning these warnings off somehow?
>
> Plus when I actually go to run it, vsnprintf() crashes the kernel, which
> usually happens if printk()'s format doesn't match the size of its
> arguments.
>
> Am I doing something really stupid here?
>
> This is using a 32-bit i386 kernel.
>

>From reading the patch I thought you had to pass the address via
reference. Otherwise you get the warning like you mention here, and then
probably an oops when the kernel tries to dereference 0x1234.

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