Re: uprobes enable condition (user space) - sysfs interface

[Masami Hiramatsu <mhiramat@kernel.org>]

On Fri, 1 Dec 2017 13:40:39 -0300
Arnaldo Carvalho de Melo <acme@kernel.org> wrote:

> Adding Masami to the CC list, to see if he can come up with a fix for
> the 'perf probe' failure below, improving the message or ignoring
> versioned symbols (with a warning perhaps).

Thanks. Should we ignore the versioned symbols? or can we put a probe
on that? If we have symbol address, we can put a probe on it, even
if it is versioned.

> 
> Em Thu, Nov 30, 2017 at 12:04:23AM +0530, bhargavb escreveu:
> > Hello,
> > 
> > I am trying to understand user space profiling using linux inbuilt
> > mechanism. (Trying with perf also but could not get complete clear
> > documentation and could not proceed, so retained linux-perf-users in
> > to list as the underlying interface used is same for both).
> 
> So yo uwant to trace function entry/exit in some userspace library? You
> can try using the tracefs as below or leave it to perf to do that, first
> you set up the probes, say for some glibc functions:
> 
> [root@jouet ~]# perf probe -F -x /lib64/libc-2.25.so  | grep ^malloc
> malloc
> malloc_check
> malloc_consolidate.part.1
> malloc_get_state@GLIBC_2.2.5
> malloc_hook_ini
> malloc_info
> malloc_printerr
> malloc_set_state@GLIBC_2.2.5
> malloc_stats
> malloc_trim
> malloc_usable_size
> mallochook
> [root@jouet ~]#
> 
> [root@jouet ~]# perf probe -x /lib64/libc-2.25.so malloc*
> Failed to write event: Invalid argument
>   Error: Failed to add events.
> [root@jouet ~]# 

OK, this is not good, at least it should analyse the reason(versioned)
and warn that (Or, I think we can just remove the suffix after "@").

> 
> For now ignore that error, its a bug I just found, what matters is that
> it _has_ put in place probes for most of those functions, as you can see
> by looking at:
> 
> [root@jouet ~]# perf probe -l
>   probe_libc:malloc    (on __malloc in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_check (on malloc_check in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_consolidate (on malloc_consolidate.part.1 in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_hook_ini (on malloc_hook_ini in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_info (on __malloc_info in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_printerr (on malloc_printerr in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_stats (on __malloc_stats in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_trim (on __malloc_trim in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_usable_size (on __malloc_usable_size in /usr/lib64/libc-2.25.so)
>   probe_libc:mallochook (on mallochook in /usr/lib64/libc-2.25.so)
> [root@jouet ~]#
> 
> Masami, this one also doesn't work:
> 
> [root@jouet ~]# perf probe -x /lib64/libc-2.25.so 'malloc*%return'
> Error: event "malloc_printerr" already exists.
> <SNIP>

Hm, this looks like a collision happens on that event name. "-f"(--force)
option allows you to add events with number suffix (e.g. _1, _2, ... )

> 
> doing it a bit differently:
> 
> [root@jouet ~]# perf probe -F -x /lib64/libc-2.25.so | egrep ^malloc[^@]+$ | while read function ; do perf probe -x /lib64/libc-2.25.so "${function}_return=$function%return" ; done
> Added new event:
>   probe_libc:malloc_check_return (on malloc_check%return in /usr/lib64/libc-2.25.so)
> 
> You can now use it in all perf tools, such as:
> 
> 	perf record -e probe_libc:malloc_check_return -aR sleep 1

Hmm, would you think we should add __return suffix by default?

Thanks,

> 
> <SNIP>
> -----------
> 
> This now makes us have:
> 
> [root@jouet ~]# perf probe -l
>   probe:check_stack_object (on check_stack_object%return@acme/git/linux/mm/usercopy.c with ret)
>   probe_libc:malloc    (on __malloc in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_check (on malloc_check in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_consolidate (on malloc_consolidate.part.1 in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_hook_ini (on malloc_hook_ini in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_info (on __malloc_info in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_printerr (on malloc_printerr in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_stats (on __malloc_stats in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_trim (on __malloc_trim in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_usable_size (on __malloc_usable_size in /usr/lib64/libc-2.25.so)
>   probe_libc:mallochook (on mallochook in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_check_return (on malloc_check%return in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_hook_ini_return (on malloc_hook_ini%return in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_info_return (on __malloc_info%return in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_printerr_return (on malloc_printerr%return in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_stats_return (on __malloc_stats%return in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_trim_return (on __malloc_trim%return in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_usable_size_return (on __malloc_usable_size%return in /usr/lib64/libc-2.25.so)
>   probe_libc:mallochook_return (on mallochook%return in /usr/lib64/libc-2.25.so)
>   probe_libc:malloc_return (on __malloc%return in /usr/lib64/libc-2.25.so)
> [root@jouet ~]# 
> 
> There were some usability snags that prevented this from being put in
> place, so do it manually:
> 
> [root@jouet ~]# perf probe -x /lib64/libc-2.25.so 'malloc_consolidate_return=malloc_consolidate.part.1%return'
> Added new event:
>   probe_libc:malloc_consolidate_return (on malloc_consolidate.part.1%return in /usr/lib64/libc-2.25.so)
> 
> You can now use it in all perf tools, such as:
> 
> 	perf record -e probe_libc:malloc_consolidate_return -aR sleep 1
> 
> [root@jouet ~]#
> 
> Ok, now we can trace this syswide using:
> 
> [root@jouet ~]# perf trace --no-syscalls -e probe_libc:*
> <BIG SNIP>
>    339.557 probe_libc:malloc:(7fda55c22970))
>    339.562 probe_libc:malloc_return:(7fda55c22970 <- 7fda55c23918))
>    339.567 probe_libc:malloc_consolidate:(7fda55c1b7b0))
>    339.570 probe_libc:malloc_consolidate_return:(7fda55c1b7b0 <- 7fda55c1f886))
>    339.596 probe_libc:malloc:(7fda55c22970))
>    339.600 probe_libc:malloc_return:(7fda55c22970 <- 7fda55c23918))
>    339.622 probe_libc:malloc:(7fda55c22970))
>    339.626 probe_libc:malloc_return:(7fda55c22970 <- 7fda56ba9a39))
>    339.631 probe_libc:malloc:(7fda55c22970))
>    339.634 probe_libc:malloc_return:(7fda55c22970 <- 7fda578f1713))
>    339.637 probe_libc:malloc:(7fda55c22970))
>    339.641 probe_libc:malloc_return:(7fda55c22970 <- 7fda578f14ae))
>    339.657 probe_libc:malloc_consolidate:(7fda55c1b7b0))
>    339.661 probe_libc:malloc_consolidate_return:(7fda55c1b7b0 <- 7fda55c1dbd6))
>    339.664 probe_libc:malloc:(7fda55c22970))
>    339.667 probe_libc:malloc_return:(7fda55c22970 <- 7fda55c23918))
>    339.670 probe_libc:malloc:(7fda55c22970))
>    339.673 probe_libc:malloc_return:(7fda55c22970 <- 7fda55c23918))
>    339.678 probe_libc:malloc_consolidate:(7fda55c1b7b0))
>    339.681 probe_libc:malloc_consolidate_return:(7fda55c1b7b0 <- 7fda55c1f886))
>    339.685 probe_libc:malloc_consolidate:(7fda55c1b7b0))
>    339.688 probe_libc:malloc_consolidate_return:(7fda55c1b7b0 <- 7fda55c1f886))
>    339.693 probe_libc:malloc_consolidate:(7fda55c1b7b0))
>    339.696 probe_libc:malloc_consolidate_return:(7fda55c1b7b0 <- 7fda55c1f886))
>    339.778 probe_libc:malloc:(7fda55c22970))
>    339.783 probe_libc:malloc_return:(7fda55c22970 <- 7fda55c23918))
>    339.788 probe_libc:malloc_consolidate:(7fda55c1b7b0))
>   ^C(7fda55c22970 <- 7fda578f14ae))
> [root@jouet ~]# 
> 
> It works as well with 'perf record' + 'perf script'.
> 
> Other features from perf can be added to the mix, like callchains, etc.
> 
> But see below for doing it via tracefs
>  
> > I observed below behaviour when I tried as per directions using URL:
> > https://opensource.com/article/17/7/dynamic-tracing-linux-user-and-kernel-space#comment-136366
> > :
> > 
> > 
> > echo 'p:<func_entry> ./test:0x420' >
> > /sys/kernel/debug/tracing/uprobe_events              (for creating
> > uprobe)
> > echo 1 > /sys/kernel/debug/tracing/events/enable
> >                                 (enabling uproble)
> > There is another enable parameter:
> > /sys/kernel/debug/tracing/events/uprobes/enable
> > 
> > I understand unless enabled both events/enable and
> > events/uprobes/enable, the /sys/kernel/debug/tracing/trace is not
> > complete. I do not understand the relevance of
> > .....events/uprobes/enable as I could not get any trace data in trace
> > log for 'func_entry' the user space function being added for tracing.
> > Irrespective of the probe function added, the trace log shows complete
> > system trace log during the period of execution of the user
> > application being traced.
> 
> Is this what you want:
> 
> [root@jouet ~]# cd /sys/kernel/debug/tracing/
> [root@jouet tracing]# cat available_tracers 
> hwlat blk mmiotrace function_graph wakeup_dl wakeup_rt wakeup function nop
> [root@jouet tracing]# echo nop > current_tracer 
> [root@jouet tracing]# echo 1 > events/probe_libc/malloc/enable 
> [root@jouet tracing]# echo 1 > tracing_on 
> [root@jouet tracing]# tail trace
>             tail-1581  [002] d... 118484.507167: malloc: (0x7fdb32d67970)
>             tail-1581  [002] d... 118484.507172: malloc: (0x7fdb32d67970)
>             tail-1581  [002] d... 118484.507189: malloc: (0x7fdb32d67970)
>             tail-1581  [002] d... 118484.507193: malloc: (0x7fdb32d67970)
>             tail-1581  [002] d... 118484.507198: malloc: (0x7fdb32d67970)
>             tail-1581  [002] d... 118484.507203: malloc: (0x7fdb32d67970)
>             tail-1581  [002] d... 118484.507208: malloc: (0x7fdb32d67970)
>             tail-1581  [002] d... 118484.507214: malloc: (0x7fdb32d67970)
>             tail-1581  [002] d... 118484.507224: malloc: (0x7fdb32d67970)
>             tail-1581  [002] d... 118484.507237: malloc: (0x7fdb32d67970)
> [root@jouet tracing]#
> 
> ?
>  
> > Can this be clearly mentioned as to when to use one of them, role of
> > both and and also, I could not see uprobe function in particular at
> > all but generic trace in /sys/kernel/debug/tracing/trace. Kindly guide
> > me in understanding uprobe enable logic in user space in detail.
> > 
> > Regards,
> > Bhargav
> > --

-- 
Masami Hiramatsu <mhiramat@kernel.org>