linux-kernel - Re: [PATCH v5 29/29] nios2: Build infrastructure

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Message-ID: <alpine.DEB.2.11.1410301148080.5308@nanos>
Date:	Thu, 30 Oct 2014 11:49:19 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ley Foon Tan <lftan@...era.com>
cc:	Arnd Bergmann <arnd@...db.de>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Chung-Lin Tang <cltang@...esourcery.com>
Subject: Re: [PATCH v5 29/29] nios2: Build infrastructure

On Thu, 30 Oct 2014, Ley Foon Tan wrote:

> On Tue, Oct 28, 2014 at 9:38 PM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Friday 24 October 2014 16:24:31 Ley Foon Tan wrote:
> >> +DECLARE_EXPORT(__gcc_bcmp);
> >> +DECLARE_EXPORT(__divdi3);
> >> +DECLARE_EXPORT(__divsi3);
> >> +DECLARE_EXPORT(__moddi3);
> >> +DECLARE_EXPORT(__modsi3);
> >> +DECLARE_EXPORT(__udivdi3);
> >> +DECLARE_EXPORT(__udivmoddi4);
> >> +DECLARE_EXPORT(__udivsi3);
> >> +DECLARE_EXPORT(__umoddi3);
> >> +DECLARE_EXPORT(__umodsi3);
> >> +DECLARE_EXPORT(__muldi3);
> >>
> >
> > I don't remember what all of these are, but at least some of them seem
> > to be concerned with 64-bit division. By convention, we don't provide those
> > in the Linux kernel but instead require all code to use the do_div()
> > macro instead.
> Do you mean kernel doesn't support 64 bit division result for a 32-bit
> architecture? Because do_div() only support 32-bit division result for
> 32-bit architecture.
> Compiler will auto generate call to __divdi3() for the following
> example code. This means loadable module will have compilation error
> if we don't export symbol for __divdi3, but built-in module is fine.
> Is this an expectation? Or we can keep 64-bit division symbols here
> since they are no harm (they are software emulation when without
> hardware divider).
> 
> long long a, b, c;
> a = b / c;

We have proper helper functions for this:

See include/linux/math.h

Thanks,

	tglx
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