linux-kernel - Re: #pragma GCC warnings (was: Re: [PATCH] crypto: drbg

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Date:	Tue, 23 Jun 2015 15:17:20 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Guenter Roeck <linux@...ck-us.net>,
	Peter Zijlstra 
	<public-peterz-wegcikhe2lqwvfeawa7xhq@...ne.gmane.org>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Jim Davis <jim.epost@...il.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Linux-Next <linux-next@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	linux-crypto@...r.kernel.org, Waiman Long <waiman.long@...com>,
	Ingo Molnar <mingo@...nel.org>, x86 <x86@...nel.org>
Subject: Re: #pragma GCC warnings (was: Re: [PATCH] crypto: drbg - use pragmas
 for disabling optimization)

Hi Stephan,

On Tue, Jun 23, 2015 at 3:01 PM, Stephan Mueller <smueller@...onox.de> wrote:
>> On Tue, Jun 23, 2015 at 11:17:23AM +0200, Geert Uytterhoeven wrote:
>> > I get that too with m68k-linux-gcc-4.6.3 and m68k-linux-gcc-4.9.0.
>> >
>> > With m68k-linux-gnu-gcc-4.1, which is still my default cross-compiler due
>> > to the good unused warning reporting, I get:
>> >
>> > crypto/jitterentropy.c:235: warning: ignoring #pragma GCC push_options
>> > crypto/jitterentropy.c:236: warning: ignoring #pragma GCC optimize
>> > crypto/jitterentropy.c:266: warning: ignoring #pragma GCC pop_options
>> > crypto/jitterentropy.c:295: warning: ignoring #pragma GCC push_options
>> > crypto/jitterentropy.c:296: warning: ignoring #pragma GCC optimize
>> > crypto/jitterentropy.c:336: warning: ignoring #pragma GCC pop_options
>> > crypto/jitterentropy.c:385: warning: ignoring #pragma GCC push_options
>> > crypto/jitterentropy.c:386: warning: ignoring #pragma GCC optimize
>> > crypto/jitterentropy.c:416: warning: ignoring #pragma GCC pop_options
>> > crypto/jitterentropy.c:517: warning: ignoring #pragma GCC push_options
>> > crypto/jitterentropy.c:518: warning: ignoring #pragma GCC optimize
>> > crypto/jitterentropy.c:580: warning: ignoring #pragma GCC pop_options
>>
>> Stephan, could you look into moving the relevant functions into
>> its own file which can then be compiled with -O0? Obviously any
>> dependency on kernel header files would have to be hidden using
>> functions outside of this file.
>
> I have separated all so far. However, there are two items left where I am not
> sure about:
>
> - asm/types.h: I need __u64

I don't expect any reliance on optimization in <asm/types.h>, as it should
just add definitions. However, "__u64" is "unsigned long long" everywhere,
so you can just use that.

> - linux/bitops.h: I need rol64
>
> Can I safely include both header files or do I have to hide them too. If yes,
> how would I do that in a way that is satisfactory?

Either open-code rol64() (it's not that complicated), or add a source file that
contains only

        #include <linux/types.h>
        #include <linux/bitops.h>

        __u64 outofline_rol64(__u64 word, unsigned int shift)
        {
                return rol64(word, shift);
        }

and call outofline_rol64() from your code.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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