linux-kernel - Re: (regression) kernel/timeconst.h bugs with HZ=128

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Message-ID: <47C4AFFC.7090500@zytor.com>
Date:	Tue, 26 Feb 2008 16:34:04 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	David Brownell <david-b@...bell.net>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.arm.linux.org.uk
Subject: Re: (regression) kernel/timeconst.h bugs with HZ=128

Andrew Morton wrote:
> On Tue, 26 Feb 2008 10:32:24 -0800 David Brownell <david-b@...bell.net> wrote:
> 
>> I see these warnings on 32 bit ARM systems:
>>
>>   CC      kernel/time.o
>> kernel/time.c: In function 'msecs_to_jiffies':
>> kernel/time.c:472: warning: integer constant is too large for 'long' type
>> kernel/time.c: In function 'usecs_to_jiffies':
>> kernel/time.c:487: warning: integer constant is too large for 'long' type
>>
>> Line 472: 
>> 	return ((u64)MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
>> line 487:
>> 	return ((u64)USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
>>
>> The problem seems to be that these constants from kernel/timeconst.h
>> have too many digits:
>>
>> #define ONLY_THIRTYTWO_BITS	0x01234567
>>
>> #define MSEC_TO_HZ_ADJ32        0x3f7ced916
>> #define USEC_TO_HZ_ADJ32        0xfffbce4217d
>>
>> Those *_ADJ32 constants should have "ULL" suffixes, yes?
>> Adding that by hand resolves the problem, but only until
>> the next time that header file gets regenerated.
>>
>> Someone with observable Perl-fu should fix this ...
>>
> 

<barf>

The real issue is that we don't have any equivalent to the UINTxx_C() 
creation macros in Linux, and even though we're using a cast -- which is 
totally correct -- makes gcc issue a (spurious) warning.

The right thing would be to create _C() macros and use those in the C 
code, i.e. UINT64_C(MSEC_TO_HZ_MUL32).

I'll write up a patch, but probably not today.

	-hpa
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