On Wed, 8 May 2019 11:22:37 -0400 Steven Rostedt <[email protected]> wrote:
> > > > Per-Probe Event Filtering > > > > ------------------------- > > > > diff --git a/Documentation/trace/uprobetracer.rst > > > > b/Documentation/trace/uprobetracer.rst > > > > index 4346e23e3ae7..de8812c932bc 100644 > > > > --- a/Documentation/trace/uprobetracer.rst > > > > +++ b/Documentation/trace/uprobetracer.rst > > > > @@ -42,16 +42,17 @@ Synopsis of uprobe_tracer > > > > @+OFFSET : Fetch memory at OFFSET (OFFSET from same file as PATH) > > > > $stackN : Fetch Nth entry of stack (N >= 0) > > > > $stack : Fetch stack address. > > > > - $retval : Fetch return value.(*) > > > > + $retval : Fetch return value.(\*1) > > > > $comm : Fetch current task comm. > > > > - +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**) > > > > + +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS > > > > address.(\*2)(\*3) > > > > NAME=FETCHARG : Set NAME as the argument name of FETCHARG. > > > > FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, > > > > basic types > > > > (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal > > > > types > > > > (x8/x16/x32/x64), "string" and bitfield are > > > > supported. > > > > > > Hmm, shouldn't uprobes default to userspace. Isn't the purpose mostly > > > to find out what's going on in userspace. Perhaps we should add a 'k' > > > annotation to uprobes to denote that it's for kernel space, as that > > > should be the exception and not the norm. > > > > No, uprobe can not access kernel space, because it doesn't have the > > current kernel context. Note that all registers, stacks which > > can be accessed from uprobe handler are user-space. We can not access > > kernel context from that. See below > > > > > > - (*) only for return probe. > > > > - (**) this is useful for fetching a field of data structures. > > > > + (\*1) only for return probe. > > > > + (\*2) this is useful for fetching a field of data structures. > > > > + (\*3) Unlike kprobe event, "u" prefix will just be ignored. > > > > Thus the 'u' is just ignored on uprobe event. > > I totally missed the footnote here. Can we stress this point more up in > the "User Memory Access" section. Specifically state something like: > "Uprobes only access userspace memory, thus the 'u' is not required, > and if it is added to a uprobe, it will simply be ignored". Sorry, I missed this mail. Since the "User Memory Access" section is only in kprobetrace.rst, I think mentioning uprobe-events in kprobetrace.rst is meaningless. Uprobe user might read uprobetracer.rst instead of kprobetrace.rst. So I think it is enough to mention it as a footnote in uprobetracer.rst. Thank you, -- Masami Hiramatsu <[email protected]>
