Clearing the direction flag before calling a signal handler

[Peter Schuller]

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Hello,

I found an exchange concerning a difficult to debug problem that may be=20
affecting FreeBSD. I wasn't sure whether to post here or just file a bug, b=
ut=20
under the circumstances I opted for the former. Apologies if it is consider=
ed=20
noise.

I was reading the exchange here:

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=3D469058

Referencing the following patch to Linux;

http://lkml.org/lkml/2008/3/5/306

The exchange in the Debian bug tracker indicates kfreebsd 6/7 has the same=
=20
problem as Linux. Being a kernel issue, that indicates vanilla FreeBSD may=
=20
likely be affected.

I neither have the setup nor the knowledge to effectively evaluate this=20
myself, but felt that it was obscure/diagnostically difficult enough that i=
=20
wanted to bring it to somebody's attention.

=2D-=20
/ Peter Schuller

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Key retrieval: Send an E-Mail to getp...@scode.org
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[Erik Trulsson]

On Sat, Mar 15, 2008 at 06:51:53PM +0100, Peter Schuller wrote:
> Hello,
>
> I found an exchange concerning a difficult to debug problem that may be

> affecting FreeBSD. I wasn't sure whether to post here or just file a bug, but
> under the circumstances I opted for the former. Apologies if it is considered

> noise.
>
> I was reading the exchange here:
>

> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=469058

>
> Referencing the following patch to Linux;
>
> http://lkml.org/lkml/2008/3/5/306
>
> The exchange in the Debian bug tracker indicates kfreebsd 6/7 has the same

> problem as Linux. Being a kernel issue, that indicates vanilla FreeBSD may

> likely be affected.
>
> I neither have the setup nor the knowledge to effectively evaluate this

> myself, but felt that it was obscure/diagnostically difficult enough that i

> wanted to bring it to somebody's attention.
>

There was also a long discussion on the gcc developers list about this
issue recently.

It seems to already have been taken care of in FreeBSD by the following
commit to -CURRENT:

kib 2008-03-13 10:54:38 UTC

FreeBSD src repository

Modified files:
sys/amd64/amd64 machdep.c
sys/amd64/ia32 ia32_signal.c
sys/amd64/linux32 linux32_sysvec.c
sys/i386/i386 machdep.c
sys/i386/linux linux_sysvec.c
sys/i386/svr4 svr4_machdep.c
sys/pc98/pc98 machdep.c
Log:
Since version 4.3, gcc changed its behaviour concerning the i386/amd64
ABI and the direction flag, that is it now assumes that the direction
flag is cleared at the entry of a function and it doesn't clear once
more if needed. This new behaviour conforms to the i386/amd64 ABI.

Modify the signal handler frame setup code to clear the DF {e,r}flags
bit on the amd64/i386 for the signal handlers.

jhb@ noted that it might break old apps if they assumed DF == 1 would be
preserved in the signal handlers, but that such apps should be rare and
that older versions of gcc would not generate such apps.

Submitted by: Aurelien Jarno <aurelien aurel32 net>
PR: 121422
Reviewed by: jhb
MFC after: 2 weeks

--
<Insert your favourite quote here.>
Erik Trulsson
ertr...@student.uu.se
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