Although debugging utilities such as strace(1) and truss(1) can trace system calls produced by a process, they can be slow and therefore not appropriate for solving performance problems on busy Unix systems. Another tool named DTrace allows you to see what happens behind the scenes on a system-wide basis without the need to modify or recompile anything. It also allows you to work on production systems and watch running programs or server processes dynamically without introducing a big overhead.
This subsection will use the dtruss(1) command-line utility that comes with macOS, which is just a dtrace(1) script that shows the system calls of a process and saves you from having to write dtrace(1) code. Note that both dtrace(1) and dtruss(1) need root privileges to run.
The output that dtruss(1) generates looks like the following:
$ sudo dtruss godoc
ioctl(0x3, 0x80086804, 0x7FFEEFBFEC20) = 0 0
close(0x3) = 0 0
access("/AppleInternal/XBS/.isChrooted ", 0x0, 0x0) = -1 Err#2
thread_selfid(0x0, 0x0, 0x0) = 1895378 0
geteuid(0x0, 0x0, 0x0) = 0 0
getegid(0x0, 0x0, 0x0) = 0 0
So, dtruss(1) works in the same way as the strace(1) utility. Analogously to strace(1), dtruss(1) will print system call counts when used with the -c parameter:
$ sudo dtruss -c go run unsafe.go 2>&1
CALL COUNT
access 1
bsdthread_register 1
getuid 1
ioctl 1
issetugid 1
kqueue 1
write 1
read 244
kevent 474
fcntl 479
lstat64 553
The preceding output will quickly inform you about potential bottlenecks in your Go code or allow you to compare the performance of two different command-line programs.
You can learn more about the dtrace(1) utility by reading DTrace: Dynamic Tracing in Oracle Solaris, Mac OS X and FreeBSD by Brendan Gregg and Jim Mauro (Prentice Hall, 2011) and by visiting http://dtrace.org/. Please bear in mind that dtrace(1) is much more powerful than strace(1) because it has its own programming language. However, strace(1) is more versatile when all you want to do is to watch the system calls of an executable file.