lkml.org 
[lkml]   [2019]   [Feb]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 5/5] tracing/probe: Support user-space dereference
Hi Steve,

Thank you for the review.

On Wed, 27 Feb 2019 21:31:32 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Wed, 27 Feb 2019 23:44:42 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> >
> > +.. _user_mem_access:
> > +User Memory Access
> > +------------------
> > +Kprobe events supports user-space memory access. For that purpose, you can use
> > +either user-space dereference syntax or 'ustring' type.
> > +
> > +user-space dereference syntax allows you to access a field of a data structure
>
> "The user-space"
>
> > +n user-space. This is done by "u" prefix with dereference syntax. For example,
>
> in user-space? "This is done by adding the "u" prefix to the dereference syntax"

Oops, it maybe a typo. yes "in user-space".
OK, I'll fix that.

>
>
> > ++u4(%si) means read a user memory from the user-space address %si+4. You can
>
> "means it will read memory from the address in the register %si offset
> by 4, and that memory is expected to be in user-space."

OK,

>
>
> > +use this for string too, e.g. +u0(%si):string means that the read a user space
>
> "for strings too"

OK,

>
> > +string from the address where %si register points. 'ustring' is a kind of
> > +short-cut. You can use +0(%si):ustring instead of that.
>
> "+u0(%si):string will read a string from the address in the register
> %si that is expected to be in user-space. 'ustring' is a shortcut way
> off performing the same task. That is, +0(%si):ustring is equivalent
> to +u0(%si):string."

Would you mean "of performing"?

>
>
> > +
> > +Note that kprobe-event provides user-memory access syntax, but it
> > doesn't +use it transparently. This means if you use normal
> > dereference or string type +for user memory, it might fail, and
> > always fails on some arch. So user has to +check if the targe data is
> > in kernel or in user space carefully.
> > Per-Probe Event Filtering
> > -------------------------
> > diff --git a/Documentation/trace/uprobetracer.rst
> > b/Documentation/trace/uprobetracer.rst index
> > 4c3bfde2ba47..6144423b2368 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.
> >
> > - (*) 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 be just ignored.
>
> "will just be ignored."

OK.

Thank you!

>
> >
> > Types
> > -----
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index 4cacbb0e1538..5408a82a015d 100644
>
>
> -- Steve


--
Masami Hiramatsu <mhiramat@kernel.org>

\
 
 \ /
  Last update: 2019-02-28 08:01    [W:0.078 / U:73.896 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site