[DTrace-devel] [PATCH v4 2/7] cg: bump number of TSLOTS to 6
Kris Van Hees
kris.van.hees at oracle.com
Thu Jul 10 04:46:15 UTC 2025
Stay tuned for a patch I will post tomorrow (Thursday) with an optimization
for the ternary operator for strings that will reduce the use of tstrings
quite a bit. With that optimization, the test you added for nested ternaries
still won't use more than 4 slots.
In the future though we should change the tstring handling to dynamically
determine the max number of slots needed for the compiled code, and allocate
based on that rather than having a hard limit.
On Wed, Jul 09, 2025 at 03:46:55PM +0100, Alan Maguire via DTrace-devel wrote:
> Because of the ternary operations using inet_ntoa*() in the
> TCP translators more temporary string slots are needed.
>
> Signed-off-by: Alan Maguire <alan.maguire at oracle.com>
> ---
> libdtrace/dt_impl.h | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/libdtrace/dt_impl.h b/libdtrace/dt_impl.h
> index 2adc1252..a47b6d40 100644
> --- a/libdtrace/dt_impl.h
> +++ b/libdtrace/dt_impl.h
> @@ -203,14 +203,16 @@ typedef struct dt_kern_path {
> #define DT_DM_KERN_UNLOADED 0x8 /* module not loaded into the kernel */
>
> /*
> - * Why do we need (only) 4 slots? The maximum amount of string arguments to
> + * Why do we need 6 slots? The maximum amount of string arguments to
> * any function is 2, and if the result is a string as well, that means we may
> * need 3 temporary strings during code generation for that function.
> + * However if operations like inet_ntoa6 are used in ternary operations we need
> + * 2x the number of slots for left and right.
> *
> * Since string functions can be nested, we can (at most) end up with 1 tstring
> * (from a nested function for which we already generated code) along with a
> * nested function being processed which needs 3 temporary strings as mentioned
> - * above. That brings us to a total of 4.
> + * above.
> *
> * Each tstring needs to be large enough to hold the largest possible string
> * and accomodate the largest known need for tstring space in subroutines.
> @@ -222,7 +224,7 @@ 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 6
> #define DT_TSTRING_SIZE(dtp) \
> MAX(P2ROUNDUP((dtp)->dt_options[DTRACEOPT_STRSIZE] + 3, 8), \
> 72)
> --
> 2.39.3
>
>
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