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Date:   Sat, 5 Aug 2017 13:56:49 +0200
From:   Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
To:     Ralf Baechle <ralf@linux-mips.org>
Cc:     linux-mips@linux-mips.org, Waldemar Brodkorb <wbx@openadk.org>
Subject: Re: undefined reference to `__multi3' when building with gcc 7.x
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Hello,

On Sat, 5 Aug 2017 00:25:00 +0200, Ralf Baechle wrote:

> > Great! However, looking at the functions that end up calling __multi3,
> > I'm wondering why suddenly gcc 7.x needs to call such a function, while
> > the same code was compiling without __multi3 in libgcc with gcc 6.x.  
> 
> Chances are it's something specific to MIPS64 R6.  Before trying your
> config file I also tried a number of other defconfigs and all built
> well.
> 
> Here's a test case which generates a reference to __multi3:
> 
> unsigned long func(unsigned long a, unsigned long b)
> {
>         return a > (~0UL) / b;
> }
> 
> GCC rearanges above statement to:
> 
> 	return (unsigned __int128)a * (unsigned __int128) b > 0xffffffff;

And this is normal/expected ?

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com