Hi Steve, Thank you for the review.
On Wed, 27 Feb 2019 21:31:32 -0500 Steven Rostedt <rost...@goodmis.org> wrote: > On Wed, 27 Feb 2019 23:44:42 +0900 > Masami Hiramatsu <mhira...@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 <mhira...@kernel.org>
