ustack
Records a user stack trace to the directed buffer.
stack ustack([uint32_t nframes, uint32_t strsize])
The ustack
function records a user stack trace to the directed buffer. The
user stack is, at most, nframes in depth. If nframes
isn't specified, the number of stack frames recorded is the number specified by the
ustackframes
option. While ustack
can determine the
address of the calling frames when the probe fires, the stack frames aren't translated into
symbols until the ustack
function is processed at user level by the DTrace
utility. If strsize is specified and is non-zero, ustack
allocates the specified amount of string space and then uses it to perform address-to-symbol
translation directly from the kernel. Such direct user symbol translation is used only with
stacktrace helpers that support this usage with DTrace. If such frames can't be translated,
the frames appear only as hexadecimal addresses.
ustack
symbol
translation occurs after the stack data is recorded. Therefore, the corresponding user process
might exit before symbol translation can be performed, making stack frame translation
impossible. If the user process exits before symbol translation is performed,
dtrace outputs a warning message, followed by the hexadecimal stack
frames.
Example 7-63 How to use ustack to trace a stack with no address-to-symbol translation
The example shows how to use ustack
to trace the stack for an
openat
system call by the date command.
sudo dtrace -qn syscall::openat:entry'/pid == $target/{ustack();}' -c 'date'
Generates output similar to the following:
CPU ID FUNCTION:NAME
2 147861 openat:entry
libc.so.6`__open64_nocancel+0x45
Mon 20 Feb 17:38:15 GMT 2023
libc.so.6`_nl_find_locale+0xfc
libc.so.6`setlocale+0x1cf
date`0x556ebae140ad
0x7a696c616d726f6e
2 147861 openat:entry
0x7f6d63fc2e65