[DTrace-devel] [PATCH v2 2/4] dt_impl: bump number of TSLOTS to 8

[Eugene Loh]

On 7/2/25 10:52, Alan Maguire wrote:

> On 01/07/2025 19:31, Eugene Loh wrote:
>> Very simple patch, but one key problem.  The changed line is preceded by
>> a huge comment block that goes to excruciating pains to explain why the
>> value should be 4.  So, I'm fine with the change itself and I think the
>> "Because of the complexity..." sentence in the commit message can be
>> dropped, but the comment block in the file needs to be updated to
>> explain (with corresponding pains?) why we need 8 (not 9, not 7).
>>
> Ah good catch, forgot to do this. I actually think 6 is enough.
> The additional seems to be a result of the various complex inet_ntoa*()
> calls in the tcp.d translators; some have ternary operators with
> multiple inet_ntoa*()s. The origin appears to be dt_cg_ternary_op() and
> that has the comment:
>
>          /*
>           * Strings complicate things a bit because dn_left and dn_right
> might
>           * actually be temporary strings (tstring) *and* in different slots.
>           * We need to allocate a new tstring to hold the result, and
> copy the
>           * value into the new tstring (and free any tstrings in dn_left and
>           * dn_right).
>           */
>
> So if we have a left and right ternary and both allocate 3 tstring slots
> for inet_ntoa*()s that means 3*2 = 6 tstring slots should actually be
> enough. Additional testing suggests that is so; does the above make
> sense or are there additional things to consider here?

Ha!  I do not know;  I prefer NOT to have a headache.  But maybe there 
should also be some tstring stress test using inet_ntoa*() and ternary ops.

> I'll update the
> next version with a comment describing the above anyhow. Thanks for the
> review!
> Alan
>
>
>> On 6/10/25 09:58, Alan Maguire wrote:
>>> Because of the complexity of the TCP translators, more tslots are
>>> needed.
>>>
>>> Signed-off-by: Alan Maguire <alan.maguire at oracle.com>
>>> ---
>>>    libdtrace/dt_impl.h | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/libdtrace/dt_impl.h b/libdtrace/dt_impl.h
>>> index 68fb8ec5..10424f9c 100644
>>> --- a/libdtrace/dt_impl.h
>>> +++ b/libdtrace/dt_impl.h
>>> @@ -218,7 +218,7 @@ typedef struct dt_kern_path {
>>>     * - cleanpath() holds a prepended '/' char, a string, an appended
>>> '/' char,
>>>     *   and a terminating NUL char, or STRSZ + 3 chars altogether
>>>     */
>>> -#define DT_TSTRING_SLOTS    4
>>> +#define DT_TSTRING_SLOTS    8
>>>    #define DT_TSTRING_SIZE(dtp)    \
>>>            MAX(P2ROUNDUP((dtp)->dt_options[DTRACEOPT_STRSIZE] + 3, 8), \
>>>                72)