linux-kernel - Re: [development-gcc] Re: do

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Message-Id: <4506767D.76E4.0078.0@novell.com>
Date:	Tue, 12 Sep 2006 07:57:33 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Andi Kleen" <ak@...e.de>
Cc:	"Michael Matz" <matz@...e.de>,
	"Richard Guenther" <rguenther@...e.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [development-gcc] Re: do_exit stuck

>Isn't a Kconfig patch missing? I don't see any place that defines 
>CONFIG_AS_CFI_SIGNAL_FRAME. Actually Kconfig wouldn't 
>be very good for this, so auto testing would be preferable
>(like the cfi test is doing) 

Using that framework was the intention (you used a CONFIG_
prefix there, and so did I), but as I wasn't sure about its status,
and as I also was doing this against plain 2.6.18-rc6, I didn't add
the actual detection logic. Actually I also think that should be
done a little differently to allow for better future extension, i.e.
instead of adding to CFLAGS store the auto-detected results in
a header and forcibly -include it.

>BTW the tree you generated it against doesn't seem to match the latest
>tree. I had to fix some rejects.

I didn't create it against your quilt tree, that's true.

>Also it would be nice if you could give a full description that could
>be used as a commit message.

Below.

>Other than that it looks good.
>
>Ok maybe a one liner comment on why UNW_DEFAULT_RA does this magic.

In order to deal with gcc's somewhat broken handling of noreturn
functions (the call instruction in which may be immediately followed
by a subsequent function, thus leading to the call's return address
pointing into that [wrong] function), add heuristics to the unwinder
to distinguish standard call frames from syscall, exception, or
interruption ones. Also provide for utilizing newer gas'
.cfi_signal_frame for non-heuristic based detection, pending
addition of the respective assembler feature detection logic.

Jan
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