Re: #pragma GCC warnings (was: Re: [PATCH] crypto: drbg - use pragmas for disabling optimization)

From: Geert Uytterhoeven
Date: Tue Jun 23 2015 - 09:17:29 EST

Hi Stephan,

On Tue, Jun 23, 2015 at 3:01 PM, Stephan Mueller <smueller@xxxxxxxxxx> 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.



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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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