Date: Sat, 17 Dec 2016 15:10:14 +0900 (JST) From: Hiroki Sato <hrs@FreeBSD.org> To: freebsd-dtrace@freebsd.org Subject: clause-local variable with copyin() Message-ID: <20161217.151014.1579687141761225852.hrs@allbsd.org>
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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.
Do I misunderstand clause-local variable? 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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