On Sun, Jul 26, 2009 at 3:35 PM, Matt Ingenthron<mingenth...@acm.org> wrote:
> Thanks again for the help Chad,
>
>> >
>> > memcached*::command-get
>> > / (signed int) arg3 != -1 /
>> > {
>> > printf("get %s, FOUND KEY\n",
>> stringof(copyin(arg1, arg2)));
>> > }
>>
>> It doesn't look like you're copying in a null
>> character, which seems
>> likely if arg2 == 5 for "setopt". You're doing the
>> copyin() the
>> second time around to a buffer that's not been
>> zeroed, and stringof()
>> is just looking for the first null character it finds
>> in that buffer.
>> It finds it after the original (if longer) string.
>
>
> I guess I'd assumed that the %s would have been treated as a clause local
> variable, but it appears that's not the case. From what you're saying, it
> appears it's a global which I can't really reference in the way I'd used it?
> That's rather confusing... but I can deal with it.
It's actually the copyin() more than the %s that's at play here. The
target memory for copyin() is scratch space. Unused space (if any) in
the principal buffer is used for scratch space. It's not global, it's
per-cpu, but it's not zeroed after use, so you can't make any
assumptions about what's there.
>
> Looking at some other examples of similar situations, it appears the best
> thing to do is create a clause local, then call stringof() on it when doing
> the printf, then zeroing it out before the next call. Does that sound like
> the right approach?
If the memory pointed to by arg1 is a null-terminated string, you
could just do this:
printf("%s\n", copyinstr(arg1));
If not, then something like this should work:
this->foo = (char *)alloca(arg2 + 1);
copyinto(arg1, arg2, this->foo);
this->foo[arg2 + 1] = '\0';
printf("%s\n", stringof(this->foo));
Chad
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