The arguments to entry
probes are the same as
the arguments to the corresponding operating system kernel
function. These arguments can be accessed as
int64_t
values by using the
arg0
, arg1
,
arg2
, ... variables.
If the function has a return value, the return value is stored
in arg1
of the return
probe. If a function does not have a return value,
arg1
is not defined.
While a given function only has a single point of entry, it
might have many different points where it returns to its caller.
FBT collects a function's multiple return sites into a single
return
probe. If you want to know the exact
return path, you can examine the return
probe
arg0
value, which indicates the offset in
bytes of the returning instruction in the function text.