Manual: argdist-bpfcc
argdist(8) System Manager's Manual argdist(8)
NAME
argdist - Trace a function and display a histogram or frequency count of its parameter values. Uses Linux eBPF/bcc.
SYNOPSIS
argdist [-h] [-p PID] [-z STRING_SIZE] [-i INTERVAL] [-d DURATION] [-n COUNT] [-v] [-T TOP] [-H specifier] [-C speciā
fier] [-I header] [-t TID]
DESCRIPTION
argdist attaches to function entry and exit points, collects specified parameter values, and stores them in a hisā
togram or a frequency collection that counts the number of times a parameter value occurred. It can also filter paraā
meter values and instrument multiple entry points at once.
Since this uses BPF, only the root user can use this tool.
REQUIREMENTS
CONFIG_BPF and bcc.
OPTIONS
-h Print usage message.
-p PID Trace only functions in the process PID.
-t TID Trace only functions in the thread TID.
-z STRING_SIZE
When collecting string arguments (of type char*), collect up to STRING_SIZE characters. Longer strings will be
truncated.
-i INTERVAL
Print the collected data every INTERVAL seconds. The default is 1 second.
-d DURATION
Total duration of trace in seconds.
-n NUMBER
Print the collected data COUNT times and then exit.
-v Display the generated BPF program, for debugging purposes.
-T TOP When collecting frequency counts, display only the top TOP entries.
-H specifiers, -C specifiers
One or more probe specifications that instruct argdist which functions to probe, which parameters to collect,
how to aggregate them, and whether to perform any filtering. See SPECIFIER SYNTAX below.
-I header
One or more header files that should be included in the BPF program. This enables the use of structure definiā
tions, enumerations, and constants that are available in these headers. You should provide the same path you
would include in the BPF program, e.g. 'linux/blkdev.h' or 'linux/time.h'. Note: in many cases, argdist will
deduce the necessary header files automatically.
SPECIFIER SYNTAX
The general specifier syntax is as follows:
{p,r,t,u}:{[library],category}:function(signature):type[,type...]:expr[,expr...][:filter]][#label]
{p,r,t,u}
Probe type - "p" for function entry, "r" for function return, "t" for kernel 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, whereas histogram probes will colā
lect the parameter values into a histogram. Only integral types can be used with histogram probes; there is
no such limitation for counting probes.
[library]
Library containing the probe. Specify the full path to the .so or executable file where the function to probe
resides. Alternatively, you can specify just the lib name: for example, "c" refers to libc. If no library name
is specified, the kernel is assumed.
category
The category of the kernel tracepoint. For example: net, sched, block.
function(signature)
The function to probe, and its signature. The function name must match exactly for the probe to be placed.
The signature, on the other hand, is only required if you plan to collect parameter values based on that sigā
nature. 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. When capturing USDT probes,
this should be the name of the probe, e.g. reloc_complete. The signature for USDT probes should be empty.
[type[,type...]]
The type(s) of the expression(s) to capture. This is the type of the keys in the histogram or raw event colā
lection that are collected by the probes.
[expr[,expr...]]
The expression(s) to capture. These are the values that are assigned to the histogram or raw event collecā
tion. You may use the parameters directly, or valid C expressions that involve the parameters, such as "size
% 10". Tracepoints may access a special structure called "args" that is formatted according to the tracepoint
format (which you can obtain using tplist). For example, the block:block_rq_complete tracepoint can access
args->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 function's execution time in nanoseconds in
$latency. Note that adding the $latency or $entry(paramname) variables to the expression will introduce an adā
ditional probe at the function's entry to collect this data, and therefore introduce additional overhead.
[filter]
The filter applied to the captured data. Only parameter values that pass the filter will be collected. This
is any valid C expression that refers to the parameter values, such as "fd == 1 && length > 16". The $entry,
$retval, and $latency variables can be used here as well, in return probes. The filter expression may also
use the STRCMP pseudo-function to compare a predefined string to a string argument. For example: STRā
CMP("test.txt", file). The order of arguments is important: the first argument MUST be a quoted literal
string, and the second argument can be a runtime string.
[label]
The label that will be displayed when printing the probed values. By default, this is the probe specifier.
EXAMPLES
Print a histogram of allocation sizes passed to kmalloc:
# argdist -H 'p::__kmalloc(u64 size):u64:size'
Print a count of how many times process 1005 called malloc with an allocation size of 16 bytes:
# argdist -p 1005 -C 'p:c:malloc(size_t size):size_t:size:size==16'
Snoop on all strings returned by gets():
# argdist -C 'r:c:gets():char*:$retval'
Print a histogram of read sizes that were longer than 1ms:
# argdist -H 'r::__vfs_read(void *file, void *buf, size_t count):size_t:$entry(count):$latency > 1000000'
Print frequency counts of how many times writes were issued to a particular file descriptor number, in process 1005:
# argdist -p 1005 -C 'p:c:write(int fd):int:fd'
Print a histogram of error codes returned by read() in process 1005:
# argdist -p 1005 -H 'r:c:read()'
Print a histogram of buffer sizes passed to write() across all processes, where the file descriptor was 1 (STDOUT):
# argdist -H 'p:c:write(int fd, const void *buf, size_t count):size_t:count:fd==1'
Count fork() calls in libc across all processes, grouped by pid:
# argdist -C 'p:c:fork():int:$PID;fork per process'
Print histogram of number of sectors in completing block I/O requests:
# argdist -H 't:block:block_rq_complete():u32:nr_sector'
Aggregate interrupts by interrupt request (IRQ):
# argdist -C 't:irq:irq_handler_entry():int:irq'
Print the functions used as thread entry points and how common they are:
# argdist -C 'u:pthread:pthread_start():u64:arg2' -p 1337
Print histograms of sleep() and nanosleep() parameter values:
# argdist -H 'p:c:sleep(u32 seconds):u32:seconds' -H 'p:c:nanosleep(struct timespec *req):long:req->tv_nsec'
Spy on writes to STDOUT performed by process 2780, up to a string size of 120 characters:
# argdist -p 2780 -z 120 -C 'p:c:write(int fd, char* buf, size_t len):char*:buf:fd==1'
Group files being read from and the read sizes from __vfs_read:
# argdist -C 'p::__vfs_read(struct file *file, void *buf, size_t count):char*,size_t:file->f_path.denā
try->d_iname,count:file->f_path.dentry->d_iname[0]!=0'
SOURCE
This is from bcc.
https://github.com/iovisor/bcc
Also look in the bcc distribution for a companion _examples.txt file containing example usage, output, and commentary
for this tool.
OS
Linux
STABILITY
Unstable - in development.
AUTHOR
Sasha Goldshtein
USER COMMANDS 2016-02-11 argdist(8)