On 8/6/2026 8:06 AM, Masami Hiramatsu (Google) wrote: > On Tue, 4 Aug 2026 01:08:40 +0200 > Peter Zijlstra <[email protected]> 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 <[email protected]> wrote: >>> >>>> On Sun, Aug 02, 2026 at 05:19:10PM +0900, Masami Hiramatsu (Google) wrote: >>>>> From: Masami Hiramatsu (Google) <[email protected]> >>>>> >>>>> 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, >
Keeping wprobe limited to kernel addresses makes sense to me. Userspace watchpoints are already supported by the perf hardware-breakpoint API, and supporting them in wprobe would add unnecessary complexity. An explicit address check could also make this boundary clear. >> >> That is, don't paint yourself in a corner etc. > >
