Crate probe

This crate provides static instrumentation macros.

With the probe! macro, programmers can place static instrumentation points in their code to mark events of interest. These are compiled into platform-specific implementations, e.g. SystemTap SDT on Linux. Probes are designed to have negligible overhead during normal operation, so they can be present in all builds, and only activated using those external tools.

Example

This simple example instruments the beginning and end of program, as well as every iteration through the loop with arguments for the counter and intermediate total.

use probe::probe;
fn main() {
    probe!(foo, begin);
    let mut total = 0;
    for i in 0..100 {
        total += i;
        probe!(foo, loop, i, total);
    }
    assert_eq!(total, 4950);
    probe!(foo, end);
}

Using probes with SystemTap

For the program above, a SystemTap script could double-check the totals:

global check

probe process.provider("foo").mark("loop") {
    check += $arg1;
    if (check != $arg2)
        printf("foo total is out of sync! (%d != %d)\n", check, $arg2);
}

// .provider is optional
probe process.mark("begin"), process.mark("end") {
    printf("%s:%s\n", $$provider, $$name);
}

Since this program behaves as expected, this script will not have any complaint.

$ stap --dyninst foo.stp -c ./foo
foo:begin
foo:end

Using probes with GDB

Starting in version 7.5, GDB can set breakpoints on probes and read arguments.

(gdb) info probes
Provider Name  Where              Semaphore Object
foo      begin 0x0000000000402e70           /tmp/foo
foo      end   0x000000000040315c           /tmp/foo
foo      loop  0x0000000000402f25           /tmp/foo
(gdb) break -probe foo:loop
Breakpoint 1 at 0x402f25
(gdb) condition 1 $_probe_arg1 > 1000
(gdb) run
Starting program: /tmp/foo
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, 0x0000000000402f25 in main::hd67360886023c1c6faa::v0.0 ()
(gdb) print $_probe_arg0
$1 = 45
(gdb) print $_probe_arg1
$2 = 1035

Macros

• probe
  Define a static probe point.
• probe_lazy
  Define a static probe point with lazy argument evaluation.