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Message-ID: <20080212193451.GE19619@redhat.com>
Date: Tue, 12 Feb 2008 14:34:51 -0500
From: "Frank Ch. Eigler" <fche@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andi Kleen <andi@...stfloor.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
Roland McGrath <roland@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [git pull] kgdb-light -v10
Hi -
On Tue, Feb 12, 2008 at 10:20:10AM -0800, Andrew Morton wrote:
> [...] Bear in mind that one of the things you do with kgdb is to
> modify kernel memory [...]
Just for completeness, keep in mind that one can already
do these sorts of things on a batch basis using systemtap:
> int foo;
> ...
> if (foo == 1)
> special_stuff();
> ...
>
> to trigger a particular behaviour at a particular time. [...]
If "foo" is a global within a particular compliation unit, any old
function in that CU can be probed to set/get the global. (Setting
incoming function parameters works too.)
# cat delayed-set.stp
# set a systemtap script variable based on a /proc control file
probe procfs("activate").write { setit = $value }
global setit
# check the systemtap global in order to set the kernel global
probe kernel.function("foo_checking_fn") {
if (setit=="1") { setit = ""; $foo = 1 }
}
# stap -g -m ds delayed-set.stp &
# echo 1 > /proc/systemtap/ds/activate
> OT: another thing you can do with kgdb is error-path testing:
> foo = kmalloc(...)
> BP-> if (!foo)
> recover();
> put a breakpoint on the !foo test and set foo to zero by hand.
# cat setit2.stp
probe kernel.statement("*@.../function.c:222") { /*if (desired)*/ $foo = 0 }
# stap -g setit2.stp &
- FChE
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