Re: memcpy regression

On Sun, Sep 06 2015, Michal Sojka wrote:

On Sun, Sep 06 2015, christophe leroy wrote:

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Le 05/09/2015 02:08, Michal Sojka a =C3=A9crit :

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On 4.9.2015 21:49, Michal Sojka wrote:

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On 4.9.2015 20:10, christophe leroy wrote:

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Le 04/09/2015 16:35, Michal Sojka a =C3=A9crit :

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On Fri, Sep 04 2015, Christophe LEROY wrote:

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Le 04/09/2015 15:33, Michal Sojka a =C3=A9crit :

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Dear Christophe,

my MPC5200-based system stopped booting recently. I bisected the=20
problem
to your commit below. If I revert that commit (on top of
807249d3ada1ff28a47c4054ca4edd479421b671 =3D v4.2-6663-g807249d), =

my

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system boots again.

Do you use mainline code only, or do you have home-made code ?

I use mainline only sources with non-mainline device-tree.

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memcpy() is not supposed to be used on non-cacheable memory.
memcpy_toio() is the function to use when copying to non-cacheble=20
area.

When I submitted the patch, I looked for erroneous use of memcpy()=

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and
memset().
I found one wrong use of memset() that I changed to memset_io() but=

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didn't find any misuse of memcpy().
But I may have missed one.

I attach my .config, if it helps. I have there

CONFIG_PPC_MPC52xx=3Dy
CONFIG_PPC_MPC5200_SIMPLE=3Dy

so arch/powerpc/platforms/52xx is probably the directory to look.=20
Do you
see any mempcy misuse there?

I only found one suspect use of memcpy() in=20
arch/powerpc/platforms/52xx/
It is in mpc52xx_pm.c but it's linked to CONFIG_PM which is not=20
selected by your .config
I'll check in the drivers selected by your .config

In parallele, are you able to try with CONFIG_PPC_EARLY_DEBUG in=20
order to try and locate the blocking point ?

I don't get any output from the system even with CONFIG_PPC_EARLY_DEBU=

G.

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Hmm, there is no udbg console for MPC5200. I hacked something up and=20
the earliest place I was able to initialize it is after=20
early_init_devtree() in setup_32.c. Even with this console, I got no=20
output when the problematic patch was applied. So the problem is=20
somewhere earlier.

In early_init() in setup_32.c, there is the following comment:
/* First zero the BSS -- use memset_io, some platforms don't have caches=

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on yet */

In that case, when does cache get activated ?

In move_device_tree(), called from early_init_devtree(), there is a call=

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to memcpy().
Can you try replacing it by memcpy_io() ?

I tried replacing it by memcpy_toio(), memcpy_fromio() and by
generic_memcpy(). Nothing helped :(

I found the problem. The compiler replaces an assignment with a call to
memcpy. The following patch fixes the problem for me. However, I'm not
sure whether this is the real solution. I guess the compiler is free to
generate a call to memcpy wherever it wants so other compilers or other
optimization levels may need fixes at other places. What do others
think?

-Michal

---------------8<----------------------
From: Michal Sojka <redacted>
Date: Sun, 6 Sep 2015 22:44:55 +0200
Subject: [PATCH] powerpc: Fix unbootable system after memcpy optimization

This fixes the problem caused by commit
0b05e2d671c40cfb57e66e4e402320d6e056b2f8. On MPC5200, when using the
following version of GCC:

    powerpc-603e-linux-gnu-gcc (OSELAS.Toolchain-2012.12.1) 4.7.2

the system was ubootable.

Signed-off-by: Michal Sojka <redacted>
---
 arch/powerpc/kernel/cputable.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index 7d80bfd..c2f1fba 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c

@@ -2121,7 +2121,7 @@ static struct cpu_spec * __init setup_cpu_spec(unsign=

ed long offset,
 	old =3D *t;
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 	/* Copy everything, then do fixups */
-	*t =3D *s;
+	memcpy_toio(t, s, sizeof(struct cpu_spec));
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 	/*
 	 * If we are overriding a previous value derived from the real
--=20
2.5.0