Re: $return in wildcarded void functions

[Vara Prasad <prasadav at us dot ibm dot com>]

Mike Mason wrote:

> [snip]
>
> probe module("uhci_hcd").function("*").return
> {
>     printf ("%s <- %s: %s\n", thread_indent(-2), probefunc(), 
> errno_str($return))
> }
My interpretation of the above statement is put a return probe in all 
the functions that have return value in the "uhci_hcd" module, with that 
interpretation we shouldn't even try to put return probes on the 
functions with a return type of void.

If the user how ever specifically says put  a probe in a function that 
has return type of void i think we should give "no return value" error.

Looks like based on dwarf info we can detect void functions. I guess the 
issue is how easy it is to carry forward the information from wild card 
expansion stage to elaboration stage so we can differentiate between the 
functions that were specified by user explicitly vs wild card expanded 
ones. I have not spent enough time to figure that out, i will let Frank 
comment on that.

> The return probe attempts to access $return.  For functions defined as 
> void, obviously there is no return value, which causes pass 2 to fail 
> with the following errors:
> semantic error: function has no return value: identifier '$return' at 
> usb2:11:85
> semantic error: function has no return value: identifier '$return' at 
> usb2:23:85
>
> Is there any way around this problem short of writing a return probe 
> for each function?  Is there any way to treat a variable as 
> conditional?  That would be a useful feature, especially for 
> wildcarded return probes.
>
> Mike