linux-kernel - Re: [PATCH -mm] timer: parenthesis fix in tbase_get

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Date:	Thu, 10 May 2007 15:02:43 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc:	"Jarek Poplawski" <jarkao2@...pl>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, "Oleg Nesterov" <oleg@...sign.ru>
Subject: Re: [PATCH -mm] timer: parenthesis fix in tbase_get_deferrable() etc.

On 5/10/07, Satyam Sharma <satyam.sharma@...il.com> wrote:
> > [...]
> > On a 64 bit system, converting pointer to int causes unnecessary
> > compiler
> > warning, and intermediate long conversion was to avoid that. I will have
>
> Whoa! Hello, hold on, just wait a second there. Do you _really_ want
> an unsigned int return out of tbase_get_deferrable() or will an
> unsigned long do? If the rest of your code is fine with unsigned long,
> then I'd suggest something like:
>
> static inline unsigned long tbase_get_deferrable(tvec_base_t *base)
> {
>         return ((unsigned long)base & TBASE_DEFERRABLE_FLAG);
> }
>
> I don't really know your code (so I could be horribly incorrect here),
> but personally I would prefer *heeding* to that warning than _hiding_
> it -- it's not unnecessary, it's telling you that you're *losing* data
> by converting a pointer (which is always unsigned long) to unsigned
> int for 64-bit platforms where sizeof(void *) == sizeof(unsigned long)
> == 8 bytes, but sizeof(unsigned int) == 4.

Oh well, pardon my obtuseness (I _really_ ought to be at least looking
around in the code before jumping in like this :-) ...
TBASE_DEFERRABLE_FLAG only {ab}uses the lowest bit of tvec_base_t *,
so clearly no pointer truncation issues here (you could still prefer
the unsigned long version for simplicity & style, though).

*embarrassed, goes for a cup of coffee*
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