Re: [PATCH v2] lib: vsprintf: Add %pa format specifier for phys_addr_t types

Geert Uytterhoeven
2013-02-07T06:39:31Z

Hi Rob,

On Thu, Feb 7, 2013 at 5:39 AM, Rob Landley <rob@landley.net> wrote:
> On 01/22/2013 06:14:53 PM, Stepan Moskovchenko wrote:
>> Add the %pa format specifier for printing a phys_addr_t
>> type and its derivative types (such as resource_size_t),
>> since the physical address size on some platforms can vary
>> based on build options, regardless of the native integer
>> type.
>>
>> Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>
>
>
> Ok, I know I'm late to the party, but doesn't LP64 apply here? Are we really
> capable of building on a target where "long" and "pointer" are different
> sizes? Last I checked the kernel was full of that assumption because there
> was an actual standard and we demanded that the compiler building us comply
> with it, just like MacOS X and the BSDs do:
>
> Standard:
> http://www.unix.org/whitepapers/64bit.html
>
> Rationale:
> http://www.unix.org/version2/whatsnew/lp64_wp.html
>
> Insane legacy reasons Windows decided to be "special":
> http://blogs.msdn.com/oldnewthing/archive/2005/01/31/363790.aspx
>
> Thus "unsigned long" should by definition be big enough. Using unsigned long
> long means you're doing 64 bit math on 32 bit targets for no apparent
> reason.
>
> What did I miss?

This is about phys_addr_t and resource_size_t, which are _physical_ addresses,
not virtual adresses. Virtual addresses are still 32-bit, so unsigned
long is fine for them.

But these days several CPUs have 36-bit physical addresses, which don't fit in
unsigned long.

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds