Re: [git pull] kgdb-light -v10

["Frank Ch. Eigler" <fche@redhat.com>]

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("*@dir/function.c:222") { /*if (desired)*/ $foo = 0 }
# stap -g setit2.stp &


- FChE