linux-kernel - Re: [PATCH] Since we have counters in __u64 format we have to print them with %llu macros.

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Message-Id: <200709261236.l8QCavNM001097@harpo.it.uu.se>
Date:	Wed, 26 Sep 2007 14:36:57 +0200 (MEST)
From:	Mikael Pettersson <mikpe@...uu.se>
To:	balbir@...ux.vnet.ibm.com, schwab@...e.de
Cc:	balbir@...ibm.com, jlan@...r.sgi.com, linux-kernel@...r.kernel.org,
	muvarov@...mvista.com
Subject: Re: [PATCH] Since we have counters in __u64 format we have to print them with %llu macros.

On Wed, 26 Sep 2007 17:18:06 +0530, Balbir Singh wrote:
> Andreas Schwab wrote:
> > Maxim Uvarov <muvarov@...mvista.com> writes:
> > 
> >> diff --git a/Documentation/accounting/getdelays.c b/Documentation/accounting/getdelays.c
> >> index cbee3a2..73924df 100644
> >> --- a/Documentation/accounting/getdelays.c
> >> +++ b/Documentation/accounting/getdelays.c
> >> @@ -208,7 +208,7 @@ void print_delayacct(struct taskstats *t)
> >>  void task_context_switch_counts(struct taskstats *t)
> >>  {
> >>  	printf("\n\nTask   %15s%15s\n"
> >> -	       "       %15lu%15lu\n",
> >> +	       "       %15llu%15llu\n",
> >>  	       "voluntary", "nonvoluntary",
> >>  	       t->nvcsw, t->nivcsw);
> > 
> > __u64 is not always long long.
> 
> What is the maximum size of long long across all architectures?
> How does one format __u64 for printing?

With %lu you get warnings when u64 is long long (32-bit).
With %llu you get warnings when u64 is plain long (most 64-bit).

Hence %llu + long long cast, i.e.:
printf("%llu", (unsigned long long)value);

This is ugly but luckily imposes no runtime overheads on
current 32- or 64-bit machines.

This could be done more cleanly if the u64 typedef also
#define:d a corresponding FMT_U64 format string.
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