* Typed locals in functions and probes? Feasibility of language enhancement?
@ 2020-07-21 2:48 Craig Ringer
2020-08-20 23:17 ` Frank Ch. Eigler
0 siblings, 1 reply; 2+ messages in thread
From: Craig Ringer @ 2020-07-21 2:48 UTC (permalink / raw)
To: systemtap
I find that I write things like this a lot:
if (foo && (@cast(foo)->bar)
return @cast(foo)->bar->baz
Because systemtap type-erases locals to long or string, code for member
access gets repetitive fast. I can @define macros for shorthand, but that
only goes so far, and it obfuscates the code a bit.
Is there an accepted pattern for this that I'm missing?
If not, how feasible would it be to track inferred types for locals?
Definitely NOT for globals, just for locals within a function? Could it be
relatively low hanging fruit to implement this, something folks here might
be able to point me in the right direction for? Or is it a major language
change that's in the too hard basket?
--
Craig Ringer http://www.2ndQuadrant.com/
2ndQuadrant - PostgreSQL Solutions for the Enterprise
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Typed locals in functions and probes? Feasibility of language enhancement?
2020-07-21 2:48 Typed locals in functions and probes? Feasibility of language enhancement? Craig Ringer
@ 2020-08-20 23:17 ` Frank Ch. Eigler
0 siblings, 0 replies; 2+ messages in thread
From: Frank Ch. Eigler @ 2020-08-20 23:17 UTC (permalink / raw)
To: Craig Ringer; +Cc: systemtap
craig wrote:
> I find that I write things like this a lot:
>
> if (foo && (@cast(foo)->bar)
> return @cast(foo)->bar->baz
>
> Because systemtap type-erases locals to long or string, code for member
> access gets repetitive fast. I can @define macros for shorthand, but that
> only goes so far, and it obfuscates the code a bit.
> Is there an accepted pattern for this that I'm missing?
Systemtap actually tries to associate some dwarf-based typing with local
variables. For example, this works:
probe kernel.function("work_busy") { f($work) }
function f(w) { ww = & @cast(w,"work_struct");
println(ww->data->counter) }
This is due to the "auto-casting" facility added to systemtap
back in 2014. I ... can't seem to find the facility actually
documented in the stap or stapprobes man page tho. See this
bit of the systemtap 2.6 release notes:
https://sourceware.org/legacy-ml/systemtap/2014-q3/msg00231.html
We could probably start tracking these types across function call
parameter-passing boundaries also. Via PR25841, functions called from a
probe handler also have some connection to the dwarf context.
- FChE
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