linux-kernel - Re: [PATCH v4 1/3] lib: add bitrev8x4()

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Message-ID: <20161202085157.1a6ec811@crub>
Date:   Fri, 2 Dec 2016 08:51:57 +0100
From:   Anatolij Gustschin <agust@...x.de>
To:     Joshua Clayton <stillcompiling@...il.com>
Cc:     Alan Tull <atull@...nsource.altera.com>,
        Moritz Fischer <moritz.fischer@...us.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 1/3] lib: add bitrev8x4()

Hi Joshua,

On Thu, 1 Dec 2016 16:04:09 -0800
Joshua Clayton stillcompiling@...il.com wrote:
...
>>> +static __always_inline __attribute_const__ u32 __arch_bitrev8x4(u32 x)
>>> +{
>>> +	__asm__ ("rbit %0, %1; rev %0, %0" : "=r" (x) : "r" (x));  
>> 	return x;  
>Oops thats a little embarrassing;
>I'll add a return.
>>> +}  
>> otherwise you get
>>
>> In function '__arch_bitrev8x4':
>> warning: no return statement in function returning non-void [-Wreturn-type]
>>
>
>I wonder why I do not see this warning when compiling. The inlining, maybe?

do you have CONFIG_HAVE_ARCH_BITREVERSE=y in your .config?
Probably not optimized code is used, otherwise you will send wrong
data to FPGA (due to wrong return values from __arch_bitrev8x4).

Anatolij