2013-03-06 01:18:37

by Dave Hansen

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Subject: %pa format specifier issues

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.


2013-03-06 02:19:56

by Stephen Boyd

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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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2013-03-06 06:30:11

by Dave Hansen

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Subject: Re: %pa format specifier issues

On 03/05/2013 06:19 PM, Stephen Boyd wrote:
>> >
>> > 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.

Heh, that would qualify as "really stupid". Thanks :)