Fair enough. You'd need to do something like this:
$1:$2:$3:$4
{
trace("hi");
}
$ sudo dtrace -s foo.d fbt kernel sys_read entry
On Sun, Nov 12, 2017 at 7:11 PM, Farhan Khan <[email protected]> wrote:
> Thank you for your response Adam!
>
> The example you provided worked with BEGIN, but failed to work on any
> other probes. For example:
>
> $ sudo dtrace -l | grep sys_read
> 32272 fbt kernel sys_read entry
>
> This is the read syscall on FreeBSD, but any example would likely function
> the same way.
>
> $ sudo dtrace -s foo.d '"fbt:kernel:sys_read:entry"'
> dtrace: failed to compile script foo.d: line 1: probe description
> :::"fbt:kernel:sys_read:entry" does not match any probes
> $ sudo dtrace -s foo.d "'fbt:kernel:sys_read:entry'"
> dtrace: failed to compile script foo.d: line 1: probe description
> :::'fbt:kernel:sys_read:entry' does not match any probes
>
> It seems to be adding the ::: string. I am not certain how to resolve this
> issue.
>
> On 11/12/2017 09:40 PM, Adam Leventhal wrote:
>
>> Hey Farhan,
>>
>> You can't use variables (e.g. self->func) as a probespec (the string that
>> specifies the set of probes to enable), but you can use command-line
>> arguments. The mistake you're making in the second example is using $$1
>> (which quotes the first command-line argument); you want to use $1. For
>> example:
>>
>> ---8<---
>> # cat foo.d
>> $1
>> {
>> trace("hi");
>> }
>> # dtrace -s foo.d BEGIN
>> dtrace: script 'foo.d' matched 1 probe
>> CPU ID FUNCTION:NAME
>> 0 1 :BEGIN hi
>> ^C
>> ---8<---
>>
>> Hopefully that helps.
>>
>>
>> A couple of notes:
>>
>> Here's an example that demonstrates where you'd use $$1:
>> dtrace -n 'BEGIN{ trace($$1) }' foo
>>
>> If you use just "$1" you'll see an error like this:
>> dtrace: invalid probe specifier BEGIN{ trace($1) }: in action list:
>> failed to resolve foo: Unknown variable name
>>
>>
>> You'll never put the $ before D variables; $variable is exclusively for
>> macros--replaced before the D language parser executes.
>>
>> Adam
>>
>>
>> On Sun, Nov 12, 2017 at 12:19 AM, Farhan Khan <[email protected] <mailto:
>> [email protected]>> wrote:
>>
>> Hi all,
>>
>> I am trying to write a generic Dtrace script that will read the
>> probe function from the console, but can't figure out the syntax. I
>> am doing this:
>>
>> # ./myscript.d "variable"
>>
>> I must use the quotes, otherwise it complains that "variable" was
>> not found. I want to do:
>>
>> dtrace:::BEGIN { self->func=$1; }
>>
>> And then:
>>
>> fbt::$self->func:entry { ... }
>>
>> However, $self->func does not seem to work. If I use $$1, it tells
>> me that the function fbt::"variable":entry does not exist, because
>> the quotes are present. When I remove the quotes from the command
>> line, it gives me that initial error.
>>
>> How do I read in a probefunc name from the console?
>>
>> Thanks,
>>
>> Farhan
>>
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