Re: [PATCH v11 04/11] tracing: wprobe: Add watchpoint probe event based on hardware breakpoint

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Tue, 4 Aug 2026 01:08:40 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Aug 04, 2026 at 08:00:35AM +0900, Masami Hiramatsu wrote:
> > On Mon, 3 Aug 2026 09:03:56 +0200
> > Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> > > On Sun, Aug 02, 2026 at 05:19:10PM +0900, Masami Hiramatsu (Google) wrote:
> > > > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > > > 
> > > > Add a new probe event for the hardware breakpoint called wprobe-event.
> > > > This wprobe allows user to trace (watch) the memory access at the
> > > > specified memory address.
> > > 
> > > s/the memory/the kernel memory/
> > 
> > Indeed.
> > 
> > > 
> > > > The new syntax is;
> > > > 
> > > >  w[:[GROUP/]EVENT] [r|w|rw]@[ADDR|SYM][:SIZE] [FETCH_ARGs]
> > > > 
> > > > User also can use $addr to fetch the accessed address and $value to fetch
> > > > the accessed memory value (shorthand for '+0($addr)'). No other variables
> > > > are supported.
> > > 
> > > This seems limited to kernel addresses only? Should not also userspace
> > > addresses be supported?
> > 
> > Hmm, for x86, yes, since it causes a trap after executing (all page fault
> > are handled). But other architecture like arm64 may not be able to support
> > it because it needs to enable watchpoint after major page fault.
> > At this step, I would like to limit it just for kernel memory.
> 
> Sure, but suppose you were to add userspace, what would the ABI be?

Ahh, sorry. It was misreading, I mean it should be only for the kernel address,
not for user space. So I don't want to add userspace. (I answered the first one)

Thank you,

> 
> That is, don't paint yourself in a corner etc.


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>