On Tue, 19 Jun 2018 09:31:49 -0700 Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote: > On 06/19/2018 09:16 AM, Masami Hiramatsu wrote: > > Add a section that explaining how to change the execution > > path with kprobes and warnings for some arch. > > > > Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx> > > Cc: Jonathan Corbet <corbet@xxxxxxx> > > Cc: linux-doc@xxxxxxxxxxxxxxx > > --- > > Documentation/kprobes.txt | 20 ++++++++++++++++++++ > > 1 file changed, 20 insertions(+) > > > > diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt > > index 3e9e99ea751b..8a98eed1521b 100644 > > --- a/Documentation/kprobes.txt > > +++ b/Documentation/kprobes.txt > > @@ -80,6 +80,26 @@ After the instruction is single-stepped, Kprobes executes the > > "post_handler," if any, that is associated with the kprobe. > > Execution then continues with the instruction following the probepoint. > > > > Hi, > I have a few small suggestions... Hi Randy, Thank you for your suggestions! All of those are good to me. I'll fix it:) Thank you! > > > > +Changing Execution Path > > +----------------------- > > + > > +Since the kprobes can probe into a running kernel code, it can change > > Since kprobes can probe into running kernel code, it can change > > > +the register set, including instruction pointer. This operation > > +requires maximum attention, such as keeping the stack frame, recovering > > +execution path etc. Since it is operated on running kernel and need deep > > Since it operates on a running kernel and needs deep > > > +knowladge of the archtecture and concurrent computing, you can easily > > knowledge of the architecture > > > +shot your foot. > > shoot > > > + > > +If you change the instruction pointer (and set up other related > > +registers) in pre_handler, you must return !0 so that the kprobes > > so that kprobes > > > +stops single stepping and just returns to given address. > > to the given address. > > > +This also means post_handler should not be called anymore. > > + > > +Note that this operation may be harder on some architectures which > > +use TOC (Table of Contents) for function call, since you have to > > +setup new TOC for your function in your module, and recover old > > setup a new TOC for your function in your module, and recover the old > > > +one after back from it. > > one after returning from it. > > > + > > Return Probes > > ------------- > > > -- > ~Randy -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
