Date: Sat, 17 Dec 2016 10:38:23 -0800 From: Matthew Ahrens <mahrens@delphix.com> To: Hiroki Sato <hrs@freebsd.org> Cc: freebsd-dtrace@freebsd.org Subject: Re: clause-local variable with copyin() Message-ID: <CAJjvXiHScMOhCb7kVoSgPHgccXkmNo_c1ysFBXnyrqj4ehJeUw@mail.gmail.com> In-Reply-To: <20161217.151014.1579687141761225852.hrs@allbsd.org> References: <20161217.151014.1579687141761225852.hrs@allbsd.org>
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On Fri, Dec 16, 2016 at 10:10 PM, Hiroki Sato <hrs@freebsd.org> wrote: > Hi, > > I have trouble with clause-local variable. A minimum working example > is attached. The "sample" program simply displays a string in an > infinite loop with a USDT named as "dump-str", sample_debug.d does > copyin() and printf() the whole buffer assuming it is > nul-terminated: > > | sample$target:::dump-str > | { > | this->st = copyin(arg0, 1024); > | > | printf("(1)st = %s, %p\n", stringof(this->st), > | (char *)this->st); > | } > | sample$target:::dump-str > | { > | printf("(2)st = %s, %p\n", stringof(this->st), > | (char *)this->st); > | printf("(3)st = %s\n", stringof(copyin(arg0, 1024))); > | } > > The odd part is that it does not work with splitting the probe into > the two as above but works fine without the split. The result was as > follows: > > | % sudo make test > | dtrace -C -I/var/home/hrs/sample_str -s sample_debug.d -c > /var/home/hrs/sample_str/sample > | dtrace: script 'sample_debug.d' matched 5 probes > | CPU ID FUNCTION:NAME > | 0 61714 main:dump-str (1)st = test-uname, > fffffe0001a19118 > | > | 0 61714 main:dump-str (2)st = , fffffe0001a19118 > | (3)st = test-uname > > this->st became empty at the beginning of the second probe. > > The symptom varied depending on the address of this->st, so I am > guessing that this->st was incorrectly freed at the end of the first > probe. If I use copyinstr(arg0) instead of copyin(), this problem > does not occur. > Perhaps this is a bug (or at least, unexpected behavior) with copyin(). I assume that it works fine with simple data types (e.g. numbers). > > Do I misunderstand clause-local variable? No, it should work as you are doing. So-called "clause-local" variables are actually implemented as "enabled-probe-local" variables I tried to test out your script on illumos but I got as far as this before running out of time: dtrace -h -s sample_probes.d gcc -c sample.c dtrace -G -s sample_probes.d sample.o gcc -o sample sample.o dtrace -s sample_debug.d -c ./sample dtrace: failed to compile script sample_debug.d: line 1: 'dump-str' is an invalid probe name --matt > I noticed this when I use > if-then clause which was recently implemented as a syntax sugar to > split a probe automatically. The following ended up with the same > result: > > | sample$target:::dump-str > | { > | this->st = copyin(arg0, 1024); > | > | printf("(1)st = %s, %p\n", stringof(this->st), > | (char *)this->st); > | if (0) { > | } > | printf("(2)st = %s, %p\n", stringof(this->st), > | (char *)this->st); > | printf("(3)st = %s\n", stringof(copyin(arg0, 1024))); > | } > > -- Hiroki >
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