From: Roland McGrath <roland@redhat.com>
To: fche@redhat.com (Frank Ch. Eigler)
Cc: dcnltc@us.ibm.com, systemtap@sourceware.org
Subject: Re: user instruction tracing patch?
Date: Wed, 14 Nov 2007 21:59:00 -0000 [thread overview]
Message-ID: <20071114215940.5A0DB26F8B6@magilla.localdomain> (raw)
In-Reply-To: Frank Ch. Eigler's message of Wednesday, 14 November 2007 16:27:57 -0500 <y0mzlxg4iw2.fsf@ton.toronto.redhat.com>
> Since utrace will provide the pt_regs structure, the probe handler
> bodies will be able to call e.g. backtrace(), probefunc(), and really
> should have some structured access to the registers (a new tapset
> function like register:long ("name") ?)
In general to access all registers you can't always use pt_regs directly;
the details vary by machine. You can get many of them on the common
machines (x86, ppc). A simple embedded-C tapset approach for each machine
is certainly an easy place to start. For full generality, you'll need to
use the formal utrace_regset interfaces instead. The elfutils libraries
have full information on mapping register names and DWARF numbers to the
formats these interfaces expose, though they could use more sugar. There
is a variety of ways you could use that info in the translator to expose
register access to the script language.
> probe process(PID).itrace if (condition) { }
So this is special syntax constrained to just testing a script variable?
Or it's any complex expression reducible to only reading global script
variables? Or what exactly?
I like this syntax when it's just a general thing for skipping out probe
hits. (In fact, you can call it awk and say it's really just a
one-statement probe body since {...} is just a statement.)
But when its real use is to cause acts that change the value of evaluating
the condition to hook into immediately changing the state of low-level
tracing features that produce the probe hits, then I want to know exactly
what the language semantics guarantees about the timely control of that state.
> probe process(PID).function("NAME") { condition = 1 }
> probe process(PID).function("NAME").return { condition = 0 }
For likely answers to my first question, doesn't seem much different from
an explicit enable/disable command, just more obscure when reading the script.
If the variable is not otherwise used, wouldn't that compile to the same as:
probe process(PID).function("NAME") { enable process(PID).itrace; }
probe process(PID).function("NAME").return { disable process(PID).itrace; }
or whatever syntax explicit enable/disable has?
Thanks,
Roland
next prev parent reply other threads:[~2007-11-14 21:59 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-13 17:58 Dave Nomura
2007-11-14 21:29 ` Frank Ch. Eigler
2007-11-14 21:59 ` Roland McGrath [this message]
2007-11-14 23:17 ` Frank Ch. Eigler
2007-11-14 23:39 ` Roland McGrath
2007-11-15 3:59 ` Frank Ch. Eigler
2007-11-16 0:04 ` Jim Keniston
2007-11-16 17:18 ` Frank Ch. Eigler
2007-11-16 18:36 ` Jim Keniston
2007-11-16 19:21 ` Frank Ch. Eigler
2007-11-16 20:20 ` Jim Keniston
2007-11-16 20:29 ` Roland McGrath
2007-11-16 20:38 ` Frank Ch. Eigler
2007-11-16 21:08 ` Jim Keniston
2007-11-16 21:25 ` Frank Ch. Eigler
2007-11-16 21:51 ` Jim Keniston
2007-11-16 22:23 ` Frank Ch. Eigler
2007-11-27 14:13 ` Dave Nomura
2007-11-27 15:14 ` Frank Ch. Eigler
2007-12-03 18:09 ` Dave Nomura
2007-12-10 18:00 ` Frank Ch. Eigler
2008-02-04 16:58 ` Dave Nomura
2008-03-10 18:49 ` Dave Nomura
2008-03-17 15:16 ` Frank Ch. Eigler
[not found] ` <47E157A8.3010508@us.ibm.com>
2008-03-19 18:42 ` Frank Ch. Eigler
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