From: fche@redhat.com (Frank Ch. Eigler)
To: Craig Ringer <craig@2ndquadrant.com>
Cc: systemtap@sourceware.org
Subject: Re: Typed locals in functions and probes? Feasibility of language enhancement?
Date: Thu, 20 Aug 2020 19:17:24 -0400 [thread overview]
Message-ID: <87eeo07vqn.fsf@redhat.com> (raw)
In-Reply-To: <CAMsr+YGv1wWciZDs6DC6md2HuJq7wAJ424uvFsfdS-v4eVRgfw@mail.gmail.com>
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
prev parent reply other threads:[~2020-08-20 23:17 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 2:48 Craig Ringer
2020-08-20 23:17 ` Frank Ch. Eigler [this message]
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