argdist, trace, and tplist support for USDT probes

These tools now support USDT probes with the 'u:provider:probe' syntax.
Probes in a library or process can be listed with 'tplist -l LIB' or 'tplist -p PID'.
Probe arguments are also parsed and available in both argdist and trace as arg1,
arg2, etc., regardless of the probe attach location.

The same USDT probe can be used at multiple locations, which means the attach infra-
structure must probe all these locations. argdist and trace register thunk probes
at each location, which call a central probe function (which is static inline) with
the location id (__loc_id). The central probe function checks the location id to
determine how the arguments should be retrieved -- this is location-dependent.

Finally, some USDT probes must be enabled first by writing a value to a memory
location (this is called a "semaphore"). This value is per-process, so we require a
process id for this kind of probes.

Along with trace and argdist tool support, this commit also introduces new classes
in the bcc module: ProcStat handles pid-wrap detection, whereas USDTReader,
USDTProbe, USDTProbeLocation, and USDTArgument are the shared USDT-related
infrastructure that enables enumeration, attachment, and argument retrieval for
USDT probes.

README.md

@@ -109,7 +109,7 @@ Examples:
 - tools/[tcpconnect](tools/tcpconnect.py): Trace TCP active connections (connect()). [Examples](tools/tcpconnect_example.txt).
 - tools/[tcpconnlat](tools/tcpconnlat.py): Trace TCP active connection latency (connect()). [Examples](tools/tcpconnlat_example.txt).
 - tools/[tcpretrans](tools/tcpretrans.py): Trace TCP retransmits and TLPs. [Examples](tools/tcpretrans_example.txt).
-- tools/[tplist](tools/tplist.py): Display kernel tracepoints and their format.
+- tools/[tplist](tools/tplist.py): Display kernel tracepoints or USDT probes and their formats. [Examples](tools/tplist_example.txt).
 - tools/[trace](tools/trace.py): Trace arbitrary functions, with filters. [Examples](tools/trace_example.txt)
 - tools/[vfscount](tools/vfscount.py) tools/[vfscount.c](tools/vfscount.c): Count VFS calls. [Examples](tools/vfscount_example.txt).
 - tools/[vfsstat](tools/vfsstat.py) tools/[vfsstat.c](tools/vfsstat.c): Count some VFS calls, with column output. [Examples](tools/vfsstat_example.txt).

man/man8/argdist.8

@@ -50,11 +50,11 @@ many cases, argdist will deduce the necessary header files automatically.
 .SH SPECIFIER SYNTAX
 The general specifier syntax is as follows:
 
-.B {p,r,t}:{[library],category}:function(signature)[:type[,type...]:expr[,expr...][:filter]][#label]
+.B {p,r,t,u}:{[library],category}:function(signature)[:type[,type...]:expr[,expr...][:filter]][#label]
 .TP
-.B {p,r,t}
+.B {p,r,t,u}
 Probe type \- "p" for function entry, "r" for function return, "t" for kernel
-tracepoint; \-H for histogram collection, \-C for frequency count.
+tracepoint, "u" for USDT probe; \-H for histogram collection, \-C for frequency count.
 Indicates where to place the probe and whether the probe should collect frequency
 count information, or aggregate the collected values into a histogram. Counting 
 probes will collect the number of times every parameter value was observed,
@@ -78,7 +78,9 @@ on the other hand, is only required if you plan to collect parameter values
 based on that signature. For example, if you only want to collect the first
 parameter, you don't have to specify the rest of the parameters in the signature.
 When capturing kernel tracepoints, this should be the name of the event, e.g.
-net_dev_start_xmit. The signature for kernel tracepoints should be empty.
+net_dev_start_xmit. The signature for kernel tracepoints should be empty. When
+capturing USDT probes, this should be the name of the probe, e.g. reloc_complete.
+The signature for USDT probes should be empty.
 .TP
 .B [type[,type...]]
 The type(s) of the expression(s) to capture.
@@ -94,6 +96,8 @@ Tracepoints may access a special structure called "tp" that is formatted accordi
 to the tracepoint format (which you can obtain using tplist). For example, the
 block:block_rq_complete tracepoint can access tp.nr_sector. You may also use the
 members of the "tp" struct directly, e.g. "nr_sector" instead of "tp.nr_sector".
+USDT probes may access the arguments defined by the tracing program in the 
+special arg1, arg2, ... variables. To obtain their types, use the tplist tool.
 Return probes can use the argument values received by the
 function when it was entered, through the $entry(paramname) special variable.
 Return probes can also access the function's return value in $retval, and the
@@ -154,6 +158,10 @@ Aggregate interrupts by interrupt request (IRQ):
 #
 .B argdist -C 't:irq:irq_handler_entry():int:irq'
 .TP
+Print the functions used as thread entry points and how common they are:
+#
+.B argdist -C 'u:pthread:pthread_start():u64:arg2' -p 1337
+.TP
 Print histograms of sleep() and nanosleep() parameter values:
 #
 .B argdist -H 'p:c:sleep(u32 seconds):u32:seconds' 'p:c:nanosleep(struct timespec *req):long:req->tv_nsec'

man/man8/tplist.8

 .TH tplist 8  "2016-03-20" "USER COMMANDS"
 .SH NAME
-tplist \- Display kernel tracepoints and their format.
+tplist \- Display kernel tracepoints or USDT probes and their formats.
 .SH SYNOPSIS
-.B tplist [-v] [tracepoint]
+.B tplist [-p PID] [-l LIB] [-v] [filter]
 .SH DESCRIPTION
 tplist lists all kernel tracepoints, and can optionally print out the tracepoint
-format; namely, the variables that you can trace when the tracepoint is hit. This
-is usually used in conjunction with the argdist and/or trace tools.
+format; namely, the variables that you can trace when the tracepoint is hit. 
+tplist can also list USDT probes embedded in a specific library or executable,
+and can list USDT probes for all the libraries loaded by a specific process.
+These features are usually used in conjunction with the argdist and/or trace tools.
 
 On a typical system, accessing the tracepoint list and format requires root.
+However, accessing USDT probes does not require root.
 .SH OPTIONS
 .TP
+\-p PID
+Display the USDT probes from all the libraries loaded by the specified process.
+.TP
+\-l LIB
+Display the USDT probes from the specified library or executable. If the librar
+or executable can be found in the standard paths, a full path is not required.
+.TP
 \-v
-Display the variables associated with the tracepoint or tracepoints.
+Display the variables associated with the tracepoint or USDT probe.
 .TP
-[tracepoint]
-A wildcard expression that specifies which tracepoints to print. For example,
-block:* will print all block tracepoints (block:block_rq_complete, etc.).
-Regular expressions are not supported.
+[filter]
+A wildcard expression that specifies which tracepoints or probes to print.
+For example, block:* will print all block tracepoints (block:block_rq_complete,
+etc.). Regular expressions are not supported.
 .SH EXAMPLES
 .TP
 Print all kernel tracepoints:
@@ -27,6 +37,14 @@ Print all kernel tracepoints:
 Print all net tracepoints with their format:
 #
 .B tplist -v 'net:*'
+.TP
+Print all USDT probes in libpthread:
+$ 
+.B tplist -l pthread
+.TP
+Print all USDT probes in process 4717 from the libc provider:
+$
+.B tplist -p 4717 'libc:*'
 .SH SOURCE
 This is from bcc.
 .IP

man/man8/trace.8

@@ -46,11 +46,11 @@ The general probe syntax is as follows:
 
 .B [{p,r}]:[library]:function [(predicate)] ["format string"[, arguments]]
 
-.B t:category:event [(predicate)] ["format string"[, arguments]]
+.B {t:category:event,u:library:probe} [(predicate)] ["format string"[, arguments]]
 .TP
-.B {[{p,r}],t}
+.B {[{p,r}],t,u}
 Probe type \- "p" for function entry, "r" for function return, "t" for kernel
-tracepoint. The default probe type is "p".
+tracepoint, "u" for USDT probe. The default probe type is "p".
 .TP
 .B [library]
 Library containing the probe.
@@ -69,6 +69,9 @@ The function to probe.
 .B event
 The tracepoint event. For example, "block_rq_complete".
 .TP
+.B probe
+The USDT probe name. For example, "pthread_create".
+.TP
 .B [(predicate)]
 The filter applied to the captured data. Only if the filter evaluates as true,
 the trace message will be printed. The filter can use any valid C expression
@@ -96,6 +99,9 @@ discover the format of your tracepoint, use the tplist tool. Note that you can
 also use the members of the "tp" struct directly, e.g "nr_sector" instead of
 "tp.nr_sector".
 
+In USDT probes, the arg1, ..., argN variables refer to the probe's arguments.
+To determine which arguments your probe has, use the tplist tool.
+
 The predicate expression and the format specifier replacements for printing
 may also use the following special keywords: $pid, $tgid to refer to the 
 current process' pid and tgid; $uid, $gid to refer to the current user's
@@ -121,6 +127,10 @@ Trace returns from the readline function in bash and print the return value as a
 Trace the block:block_rq_complete tracepoint and print the number of sectors completed:
 #
 .B trace 't:block:block_rq_complete """%d sectors"", nr_sector'
+.TP
+Trace the pthread_create USDT probe from the pthread library and print the address of the thread's start function:
+#
+.B trace 'u:pthread:pthread_create """start addr = %llx"", arg3'
 .SH SOURCE
 This is from bcc.
 .IP

src/python/bcc/__init__.py

@@ -26,6 +26,7 @@ import sys
 basestring = (unicode if sys.version_info[0] < 3 else str)
 
 from .libbcc import lib, _CB_TYPE
+from .procstat import ProcStat
 from .table import Table
 from .tracepoint import Perf, Tracepoint
 from .usyms import ProcessSymbols
@@ -341,7 +342,7 @@ class BPF(object):
                 desc.encode("ascii"), pid, cpu, group_fd,
                 self._reader_cb_impl, ct.cast(id(self), ct.py_object))
         res = ct.cast(res, ct.c_void_p)
-        if res.value is None:
+        if res == None:
             raise Exception("Failed to attach BPF to kprobe")
         open_kprobes[ev_name] = res
         return self
@@ -389,7 +390,7 @@ class BPF(object):
                 desc.encode("ascii"), pid, cpu, group_fd,
                 self._reader_cb_impl, ct.cast(id(self), ct.py_object))
         res = ct.cast(res, ct.c_void_p)
-        if res.value is None:
+        if res == None:
             raise Exception("Failed to attach BPF to kprobe")
         open_kprobes[ev_name] = res
         return self
@@ -513,7 +514,7 @@ class BPF(object):
                 desc.encode("ascii"), pid, cpu, group_fd,
                 self._reader_cb_impl, ct.cast(id(self), ct.py_object))
         res = ct.cast(res, ct.c_void_p)
-        if res.value is None:
+        if res == None:
             raise Exception("Failed to attach BPF to uprobe")
         open_uprobes[ev_name] = res
         return self
@@ -557,7 +558,7 @@ class BPF(object):
                 desc.encode("ascii"), pid, cpu, group_fd,
                 self._reader_cb_impl, ct.cast(id(self), ct.py_object))
         res = ct.cast(res, ct.c_void_p)
-        if res.value is None:
+        if res == None:
             raise Exception("Failed to attach BPF to uprobe")
         open_uprobes[ev_name] = res
         return self
@@ -793,3 +794,5 @@ class BPF(object):
         except KeyboardInterrupt:
             exit()
 
+from .usdt import USDTReader
+

src/python/bcc/procstat.py

+# Copyright 2016 Sasha Goldshtein
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+
+class ProcStat(object):
+        def __init__(self, pid):
+                self.pid = pid
+                self.exe = self._get_exe()
+                self.start_time = self._get_start_time()
+
+        def is_stale(self):
+                return self.exe != self._get_exe() or \
+                       self.start_time != self._get_start_time()
+
+        def _get_exe(self):
+                return os.popen("readlink -f /proc/%d/exe" % self.pid).read()
+
+        def _get_start_time(self):
+                return os.popen("cut -d' ' -f 22 /proc/%d/stat" %
+                                self.pid).read()
+

src/python/bcc/usyms.py

@@ -27,16 +27,7 @@ class ProcessSymbols(object):
     def refresh_code_ranges(self):
         self.code_ranges = self._get_code_ranges()
         self.ranges_cache = {}
-        self.exe = self._get_exe()
-        self.start_time = self._get_start_time()
-
-    def _get_exe(self):
-        return ProcessSymbols._run_command_get_output(
-                "readlink -f /proc/%d/exe" % self.pid)
-
-    def _get_start_time(self):
-        return ProcessSymbols._run_command_get_output(
-                "cut -d' ' -f 22 /proc/%d/stat" % self.pid)
+        self.procstat = ProcStat(self.pid)
 
     @staticmethod
     def _is_binary_segment(parts):
@@ -101,10 +92,7 @@ class ProcessSymbols(object):
         return "%x" % offset
 
     def _check_pid_wrap(self):
-        # If the pid wrapped, our exe name and start time must have changed.
-        # Detect this and get rid of the cached ranges.
-        if self.exe != self._get_exe() or \
-           self.start_time != self._get_start_time():
+        if self.procstat.is_stale():
             self.refresh_code_ranges()
 
     def decode_addr(self, addr):
@@ -127,3 +115,4 @@ class ProcessSymbols(object):
                                     binary)
         return "%x" % addr
 
+from . import ProcStat

tools/argdist_example.txt

@@ -332,9 +332,10 @@ optional arguments:
                         additional header files to include in the BPF program
 
 Probe specifier syntax:
-        {p,r,t}:{[library],category}:function(signature)[:type[,type...]:expr[,expr...][:filter]][#label]
+        {p,r,t,u}:{[library],category}:function(signature)[:type[,type...]:expr[,expr...][:filter]][#label]
 Where:
-        p,r,t      -- probe at function entry, function exit, or kernel tracepoint
+        p,r,t,u    -- probe at function entry, function exit, kernel tracepoint,
+                      or USDT probe
                       in exit probes: can use $retval, $entry(param), $latency
         library    -- the library that contains the function
                       (leave empty for kernel functions)
@@ -392,6 +393,10 @@ argdist -H 't:block:block_rq_complete():u32:tp.nr_sector'
 argdist -C 't:irq:irq_handler_entry():int:tp.irq'
         Aggregate interrupts by interrupt request (IRQ)
 
+argdist -C 'u:pthread:pthread_start():u64:arg2' -p 1337
+        Print frequency of function addresses used as a pthread start function,
+        relying on the USDT pthread_start probe in process 1337
+
 argdist -H \
         'p:c:sleep(u32 seconds):u32:seconds' \
         'p:c:nanosleep(struct timespec *req):long:req->tv_nsec'

tools/tplist.py

 #!/usr/bin/env python
 #
-# tplist    Display kernel tracepoints and their formats.
+# tplist    Display kernel tracepoints or USDT probes and their formats.
 #
-# USAGE:    tplist [-v] [tracepoint]
+# USAGE:    tplist [-p PID] [-l LIB] [-v] [filter]
 #
 # Licensed under the Apache License, Version 2.0 (the "License")
 # Copyright (C) 2016 Sasha Goldshtein.
 
 import argparse
 import fnmatch
-import re
 import os
+import re
+import sys
+
+from bcc import USDTReader
 
 trace_root = "/sys/kernel/debug/tracing"
 event_root = os.path.join(trace_root, "events")
 
 parser = argparse.ArgumentParser(description=
-                "Display kernel tracepoints and their formats.",
+                "Display kernel tracepoints or USDT probes and their formats.",
                 formatter_class=argparse.RawDescriptionHelpFormatter)
+parser.add_argument("-p", "--pid", type=int, default=-1, help=
+                "List USDT probes in the specified process")
+parser.add_argument("-l", "--lib", default="", help=
+                "List USDT probes in the specified library or executable")
 parser.add_argument("-v", dest="variables", action="store_true", help=
-                "Print the format (available variables) for each tracepoint")
-parser.add_argument(dest="tracepoint", nargs="?",
-                help="The tracepoint name to print (wildcards allowed)")
+                "Print the format (available variables)")
+parser.add_argument(dest="filter", nargs="?", help=
+                "A filter that specifies which probes/tracepoints to print")
 args = parser.parse_args()
 
 def print_tpoint_format(category, event):
@@ -42,12 +49,12 @@ def print_tpoint_format(category, event):
 
 def print_tpoint(category, event):
         tpoint = "%s:%s" % (category, event)
-        if not args.tracepoint or fnmatch.fnmatch(tpoint, args.tracepoint):
+        if not args.filter or fnmatch.fnmatch(tpoint, args.filter):
                 print(tpoint)
                 if args.variables:
                         print_tpoint_format(category, event)
 
-def print_all():
+def print_tracepoints():
         for category in os.listdir(event_root):
                 cat_dir = os.path.join(event_root, category)
                 if not os.path.isdir(cat_dir):
@@ -57,5 +64,28 @@ def print_all():
                         if os.path.isdir(evt_dir):
                                 print_tpoint(category, event)
 
+def print_usdt(pid, lib):
+        reader = USDTReader(bin_path=lib, pid=pid)
+        probes_seen = []
+        for probe in reader.probes:
+                probe_name = "%s:%s" % (probe.provider, probe.name)
+                if not args.filter or fnmatch.fnmatch(probe_name, args.filter):
+                        if probe_name in probes_seen:
+                                continue
+                        probes_seen.append(probe_name)
+                        if args.variables:
+                                print(probe.display_verbose())
+                        else:
+                                print("%s %s:%s" % (probe.bin_path,
+                                        probe.provider, probe.name))
+
 if __name__ == "__main__":
-        print_all()
+        try:
+                if args.pid != -1 or args.lib != "":
+                        print_usdt(args.pid, args.lib)
+                else:
+                        print_tracepoints()
+        except:
+                if sys.exc_type is not SystemExit:
+                        print(sys.exc_value)
+

tools/tplist_example.txt

+Demonstrations of tplist.
+
+
+tplist displays kernel tracepoints and USDT probes, including their
+format. It can be used to discover probe points for use with the trace
+and argdist tools. Kernel tracepoints are scattered around the kernel
+and provide valuable static tracing on block and network I/O, scheduling,
+power events, and many other subjects. USDT probes are placed in libraries
+(such as libc) and executables (such as node) and provide static tracing
+information that can (optionally) be turned on and off at runtime.
+
+For example, suppose you want to discover which USDT probes a particular
+executable contains. Just run tplist on that executable (or library):
+
+$ tplist -l basic_usdt
+/home/vagrant/basic_usdt basic_usdt:start_main
+/home/vagrant/basic_usdt basic_usdt:loop_iter
+/home/vagrant/basic_usdt basic_usdt:end_main
+
+The loop_iter probe sounds interesting. What are the locations of that
+probe, and which variables are available?
+
+$ tplist '*loop_iter' -l basic_usdt -v
+/home/vagrant/basic_usdt basic_usdt:loop_iter [sema 0x601036]
+  location 0x400550 raw args: -4@$42 8@%rax
+    4   signed bytes @ constant 42
+    8 unsigned bytes @ register %rax
+  location 0x40056f raw args: 8@-8(%rbp) 8@%rax
+    8 unsigned bytes @ -8(%rbp)
+    8 unsigned bytes @ register %rax
+
+This output indicates that the loop_iter probe is used in two locations
+in the basic_usdt executable. The first location passes a constant value,
+42, to the probe. The second location passes a variable value located at
+an offset from the %rbp register. Don't worry -- you don't have to trace
+the register values yourself. The argdist and trace tools understand the
+probe format and can print out the arguments automatically -- you can
+refer to them as arg1, arg2, and so on.
+
+Try to explore with some common libraries on your system and see if they
+contain UDST probes. Here are two examples you might find interesting:
+
+$ tplist -l pthread     # list probes in libpthread
+/lib64/libpthread.so.0 libpthread:pthread_start
+/lib64/libpthread.so.0 libpthread:pthread_create
+/lib64/libpthread.so.0 libpthread:pthread_join
+/lib64/libpthread.so.0 libpthread:pthread_join_ret
+/lib64/libpthread.so.0 libpthread:mutex_init
+... more output truncated
+
+$ tplist -l c           # list probes in libc
+/lib64/libc.so.6 libc:setjmp
+/lib64/libc.so.6 libc:longjmp
+/lib64/libc.so.6 libc:longjmp_target
+/lib64/libc.so.6 libc:memory_arena_reuse_free_list
+/lib64/libc.so.6 libc:memory_heap_new
+... more output truncated
+
+tplist also understands kernel tracepoints, and can list their format
+as well. For example, let's look for all block I/O-related tracepoints:
+
+# tplist 'block*'
+block:block_touch_buffer
+block:block_dirty_buffer
+block:block_rq_abort
+block:block_rq_requeue
+block:block_rq_complete
+block:block_rq_insert
+block:block_rq_issue
+block:block_bio_bounce
+block:block_bio_complete
+block:block_bio_backmerge
+block:block_bio_frontmerge
+block:block_bio_queue
+block:block_getrq
+block:block_sleeprq
+block:block_plug
+block:block_unplug
+block:block_split
+block:block_bio_remap
+block:block_rq_remap
+
+The block:block_rq_complete tracepoints sounds interesting. Let's print
+its format to see what we can trace with argdist and trace:
+
+$ tplist -v block:block_rq_complete
+block:block_rq_complete
+    dev_t dev;
+    sector_t sector;
+    unsigned int nr_sector;
+    int errors;
+    char rwbs[8];
+
+The dev, sector, nr_sector, etc. variables can now all be used in probes
+you specify with argdist or trace.
+
+
+USAGE message:
+
+$ tplist -h
+usage: tplist.py [-h] [-p PID] [-l LIB] [-v] [filter]
+
+Display kernel tracepoints or USDT probes and their formats.
+
+positional arguments:
+  filter             A filter that specifies which probes/tracepoints to print
+
+optional arguments:
+  -h, --help         show this help message and exit
+  -p PID, --pid PID  List USDT probes in the specified process
+  -l LIB, --lib LIB  List USDT probes in the specified library or executable
+  -v                 Print the format (available variables)
+

tools/trace_example.txt

@@ -171,4 +171,6 @@ trace 'r:c:malloc (retval) "allocated = %p", retval
         Trace returns from malloc and print non-NULL allocated buffers
 trace 't:block:block_rq_complete "sectors=%d", tp.nr_sector'
         Trace the block_rq_complete kernel tracepoint and print # of tx sectors
+trace 'u:pthread:pthread_create (arg4 != 0)'
+        Trace the USDT probe pthread_create when its 4th argument is non-zero