[DTrace-devel] [PATCH] Allow tstrings to persist across clause boundaries within a program

[Eugene Loh]

I'd like to hear more about how this fits into strtok.  For example, 
does this bump DT_TSTRING_SLOTS up from 4 to 5?  Or, would the number of 
slots be bumped up if and only if any clause for any probe uses strtok?

Also, we currently assume that stack actions and string subroutines are 
never co-active.  That is, the space we allocate for stacks and for 
tstrings overlap one another and we allocate only enough space for the 
MAX() of the two.  But if two strtok() calls are separated by a stack 
call, then the strtok internal string would seem to get corrupted with 
such a space-saving scheme.

I started looking at strtok and I simply allocated another string at the 
end of the MAX(tstring, stack) area.  That is potentially wasteful but 
it's easy.

On 11/2/21 1:35 AM, Kris Van Hees wrote:
> The upcoming strtok() implementation has a need to store the string to
> be tokenized in a temporary string (tstring).  The strtok() semantics
> require that source string to persist across clause boundaries within
> a given probe firing.  That means the tstrings needs to persist for
> the duration of the probe program.
>
> Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> ---
>   libdtrace/dt_cc.c   | 2 ++
>   libdtrace/dt_cg.c   | 3 +--
>   libdtrace/dt_impl.h | 2 ++
>   3 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/libdtrace/dt_cc.c b/libdtrace/dt_cc.c
> index a25f3548..08bc9438 100644
> --- a/libdtrace/dt_cc.c
> +++ b/libdtrace/dt_cc.c
> @@ -1996,6 +1996,8 @@ dt_compile(dtrace_hdl_t *dtp, int context, dtrace_probespec_t pspec, void *arg,
>   		    "not referenced)\n", yypcb->pcb_sargv[argc - 1], argc - 1);
>   	}
>   
> +	dt_cg_tstring_reset(dtp);
> +
>   	/*
>   	 * If we have successfully created a parse tree for a D program, loop
>   	 * over the clauses and actions and instantiate the corresponding
> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> index 0196b114..6a4500a5 100644
> --- a/libdtrace/dt_cg.c
> +++ b/libdtrace/dt_cg.c
> @@ -801,7 +801,7 @@ dt_cg_spill_load(int reg)
>   /*
>    * Initialize the temporary string offsets and mark all not in use.
>    */
> -static void
> +void
>   dt_cg_tstring_reset(dtrace_hdl_t *dtp)
>   {
>   	int		i;
> @@ -5654,7 +5654,6 @@ dt_cg(dt_pcb_t *pcb, dt_node_t *dnp)
>   	}
>   
>   	dt_regset_reset(pcb->pcb_regs);
> -	dt_cg_tstring_reset(pcb->pcb_hdl);
>   
>   	dt_irlist_destroy(&pcb->pcb_ir);
>   	dt_irlist_create(&pcb->pcb_ir);
> diff --git a/libdtrace/dt_impl.h b/libdtrace/dt_impl.h
> index b461d73d..3be62657 100644
> --- a/libdtrace/dt_impl.h
> +++ b/libdtrace/dt_impl.h
> @@ -760,6 +760,8 @@ extern dtrace_difo_t *dt_dlib_get_func_difo(dtrace_hdl_t *, const dt_ident_t *);
>   extern void dt_dlib_reset(dtrace_hdl_t *dtp, boolean_t);
>   extern int dt_load_libs(dtrace_hdl_t *dtp);
>   
> +extern void dt_cg_tstring_reset(dtrace_hdl_t *dtp);
> +
>   extern void *dt_compile(dtrace_hdl_t *dtp, int context,
>   			dtrace_probespec_t pspec, void *arg, uint_t cflags,
>   			int argc, char *const argv[], FILE *fp, const char *s);