Fix unaligned access

Fix unaligned access

[Andreas Schwab]

This fixes an unaligned access during nscd communication.

Andreas.

2005-07-13  Andreas Schwab  <schwab@suse.de>

	* nscd/nscd_helper.c (get_mapping): Align control message buffer.

--- nscd/nscd_helper.c.~1.10.~	2005-02-23 11:25:53.000000000 +0100
+++ nscd/nscd_helper.c	2005-07-13 11:54:38.000000000 +0200
@@ -176,7 +176,7 @@ get_mapping (request_type type, const ch
   iov[0].iov_base = resdata;
   iov[0].iov_len = keylen;
 
-  char buf[CMSG_SPACE (sizeof (int))];
+  char buf[CMSG_SPACE (sizeof (int))] __attribute__ ((aligned));
   struct msghdr msg = { .msg_iov = iov, .msg_iovlen = 1,
 			.msg_control = buf, .msg_controllen = sizeof (buf) };
   struct cmsghdr *cmsg = CMSG_FIRSTHDR (&msg);

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: Fix unaligned access

[Ulrich Drepper]

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Andreas Schwab wrote:
> This fixes an unaligned access during nscd communication.

When and where?

-- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖


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Re: Fix unaligned access

[Andreas Schwab]

Ulrich Drepper <drepper@redhat.com> writes:

> Andreas Schwab wrote:
>> This fixes an unaligned access during nscd communication.
>
> When and where?

When this function is called???

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: Fix unaligned access

[Ulrich Drepper]

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And again: when and where is this a problem?

I cannot believe it has to be asked.  Those of us actually looking at
bug reports need to know the circumstances to determine whether the fix
might cure the problem.  If this would be a general problem it would
long have shown up.

-- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖


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Re: Fix unaligned access

[Andreas Schwab]

Ulrich Drepper <drepper@redhat.com> writes:

> And again: when and where is this a problem?

See a few lines below:

  cmsg->cmsg_level = SOL_SOCKET;

Since cmsg is just a pointer to msg.msg_control, this needs to be properly
aligned.  Same for the next three lines.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: Fix unaligned access

[Ulrich Drepper]

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Andreas Schwab wrote:
> Since cmsg is just a pointer to msg.msg_control, this needs to be properly
> aligned.  Same for the next three lines.

You don't get it.  Which architecture, what kind of build?

-- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖


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Re: Fix unaligned access

[Andreas Schwab]

Ulrich Drepper <drepper@redhat.com> writes:

> You don't get it.

You might want to be more specific with your questions the next time.  I
can't read your mind.

>  Which architecture,

Any architecture that can report unaligned accesses, which includes the
ia64.

> what kind of build?

Care to expand?

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: Fix unaligned access

[Ulrich Drepper]

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Andreas Schwab wrote:
> Any architecture that can report unaligned accesses, which includes the
> ia64.

Not in all cases.


>>what kind of build?
> 
> Care to expand?

I haven't seen any such message so it cannot happen in all builds.  So
you probably did something special.

-- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖


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Re: Fix unaligned access

[Andreas Schwab]

Ulrich Drepper <drepper@redhat.com> writes:

> I haven't seen any such message so it cannot happen in all builds.

So what?  That's the basic principle of undefined behaviour.

I don't understand all the fuss you made.  If you like to see the bug
solved differently please say so in the first place in clear and
understandable words.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."