Check a call function is available for a probe type

[mmisono]

Some call functions (e.g., reg()) is not available for some probe types. To check this, add check_available(call, type) function. This function returns true if the call is available for that type. Also, disable reg() in k(ret)func using this function. Previously that is mistakenly allowed and resulted in invalid BPF codes.

Checklist

• Language changes are updated in docs/reference_guide.md
• User-visible and non-trivial changes updated in CHANGELOG.md
• The new behaviour is covered by tests

[mmisono]

This is a continuation of #1380. kfunc reg() tests would conflicts #1641.

[fbs]

can we move this to the top and then remove all the invalid cases from the switch statements? Or does that trigger a missing case warning?

[mmisono]

yes, -Wswitch emits warnings. warning: enumeration value 'invalid' not handled in switch [-Wswitch]

[mmisono]

rebased and update tests since #1641 is just merged.

[danobi]

We can make a call to check_available(..) at the beginning of the function and delete the other callsites right? Would reduce duplicated code (especially the loop).

[fbs]

I wonder if its doable to write a simple spec for each call that handles this and all the other standard check things for calls (and builtins). E.g.

CallSpec {
 .name = "str",
 .probe_types = any,
 .required_features = {somefeature},
 .min_args = 1,
 .max_args = 2,
 .arg_types = [
  [{ type = integer, literal = true}, { type = pointer } ], // arg0
  [{ type = integer }], // arg1
  .func = &semantic_analyser::call_str
]}

It would remove quite a bit of basically duplicate code everywhere, the deep nested long functions and would help standardize error messages. It should also make it easier to get a quick overview of the calls we have an what kind of arguments they take, might even be possible to generate nice help format output from it.

But there probably are some cases that make it hard to do

[fbs]

Feels like we now need to keep track of this in two places. We have to update check_available to reflect the probe types and then update the error message too. Can't we update check_available to output the err msg, the other checks do it as well.

Changing the signature to check_available(Call &c, std::vector<probetype &> t) might make that easier too.

[mmisono]

I changed so that the error messages are printed out when check_available() failed.
6fcf1a7#diff-042d9701e67f79452452faac3c625c3ca83e7692abd3274956abe30d58ae0c39R459-R467

[mmisono]

fbs's proposal seems great. For now, I implemented danobi's suggestion.

[mmisono]

rebased