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Re: [PATCH] crypto: drbg - use pragmas for disabling optimization

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  Re: [PATCH] crypto: drbg - use pragmas for disabling optimization Guenter Roeck <linux@roeck-us.net> - 2015-06-09 06:40 +0200
    nios2: Export get_cycles Herbert Xu <herbert@gondor.apana.org.au> - 2015-06-09 06:50 +0200

#1160971 — Re: [PATCH] crypto: drbg - use pragmas for disabling optimization

On 06/08/2015 07:08 PM, Stephan Mueller wrote:
> Hi,
>
> I performed measurements of the upper and lower boundary of the minimum and
> Shannon entropy for the RNG before the patch and after the patch. The values
> are very similar which demonstrates that the change does not affect the
> cryptographic characteristics of the RNG.
>
> The tests are available at:
>
> [1] shows the lower boundary of the fully non-optimized RNG
>
> [2] shows the lower boundary of the RNG with the patch below
>
> [3] shows the upper boundary of the fully non-optimized RNG
>
> [4] shows the upper boundary of the RNG with the patch below
>
> The pictures are fully explained in [5], but the key values are the minimum
> and Shannon entropy numbers in the legend of the graphs.
>
> [1] http://www.eperm.de/userspace-foldtime-testO0.data-single-time-dist-delta-3036-hist.pdf
>
> [2] http://www.eperm.de/userspace-foldtime-test-pragmas-O2.data-single-time-dist-delta-2370-hist.pdf
>
> [3] http://www.eperm.de/userspace-foldtime-testO0.data-varying-time-dist-delta-7302-hist.pdf
>
> [4] http://www.eperm.de/userspace-foldtime-test-pragmas-O2.data-varying-time-dist-delta-7055-hist.pdf
>
> [5] http://www.chronox.de/jent/doc/CPU-Jitter-NPTRNG.pdf
>
> ---8<---
> Replace the global -O0 compiler flag from the Makefile with GCC
> pragmas to mark only the functions required to be compiled without
> optimizations.
>
> This patch also adds a comment describing the rationale for the
> functions chosen to be compiled without optimizations.
>
> Signed-off-by: Stephan Mueller <smueller@chronox.de>

With openrisc, I get:

   CC [M]  crypto/jitterentropy.o
crypto/jitterentropy.c:266:9: warning: #pragma GCC target is not supported for this machine

which may not be perfect, but is better than a compile error ;-).

nios2 still fails to build with

ERROR: "get_cycles" [crypto/jitterentropy.ko] undefined!

Guenter



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#1160975 — nios2: Export get_cycles

On Mon, Jun 08, 2015 at 09:31:54PM -0700, Guenter Roeck wrote:
> 
> nios2 still fails to build with
> 
> ERROR: "get_cycles" [crypto/jitterentropy.ko] undefined!

It's the only arch that doesn't inline get_cycles and doesn't
export it.

---8<---
nios2 is the only architecture that does not inline get_cycles
and does not export it.  This breaks crypto as it uses get_cycles
in a number of modules.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/arch/nios2/kernel/time.c b/arch/nios2/kernel/time.c
index 7f45474..be186a7 100644
--- a/arch/nios2/kernel/time.c
+++ b/arch/nios2/kernel/time.c
@@ -8,6 +8,7 @@
  * for more details.
  */
 
+#include <linux/export.h>
 #include <linux/interrupt.h>
 #include <linux/clockchips.h>
 #include <linux/clocksource.h>
@@ -106,6 +107,7 @@ cycles_t get_cycles(void)
 {
 	return nios2_timer_read(&nios2_cs.cs);
 }
+EXPORT_SYMBOL(get_cycles);
 
 static void nios2_timer_start(struct nios2_timer *timer)
 {
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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