[DTrace-devel] [PATCH v3 15/19] Ignore clauses: some clauses are impossible regardless of uprp

[Kris Van Hees]

On Fri, Oct 25, 2024 at 02:34:23AM -0400, eugene.loh at oracle.com wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
> 
> In ignore_clauses, for an underlying probe uprp, we try to
> decide if we can safely ignore clause n.
> 
> Meanwhile, for some clauses, the probe description tells us the
> clause will not be called for any USDT probe, regardless of the
> underlying probe.  For example, "syscall::write:" can safely be
> ignored, for all uprp.
> 
> Add clause flags to track a statement's status.  Specifically,
> a flag may indicate that a statement can be excluded for every
> possible USDT probe or included because it might be needed for
> some possible USDT probe.
> 
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>

Reviewed-by: Kris Van Hees <kris.van.hees at oracle.com>

> ---
>  libdtrace/dt_program.c     | 15 +++++++++++
>  libdtrace/dt_program.h     |  3 +++
>  libdtrace/dt_prov_uprobe.c | 53 ++++++++++++++++++++++++++++++++++++--
>  libdtrace/dtrace.h         |  2 ++
>  4 files changed, 71 insertions(+), 2 deletions(-)
> 
> diff --git a/libdtrace/dt_program.c b/libdtrace/dt_program.c
> index 45da4f206..23b91fb2e 100644
> --- a/libdtrace/dt_program.c
> +++ b/libdtrace/dt_program.c
> @@ -20,6 +20,21 @@
>  #include <dt_probe.h>
>  #include <dt_bpf.h>
>  
> +int
> +dt_stmt_clsflag_set(dtrace_stmtdesc_t *stp, int flags) {
> +	stp->dtsd_clauseflags |= flags;
> +
> +	return 0;
> +}
> +
> +int
> +dt_stmt_clsflag_test(dtrace_stmtdesc_t *stp, int flags) {
> +	if (stp->dtsd_clauseflags & flags)
> +		return 1;
> +
> +	return 0;
> +}
> +
>  dtrace_prog_t *
>  dt_program_create(dtrace_hdl_t *dtp)
>  {
> diff --git a/libdtrace/dt_program.h b/libdtrace/dt_program.h
> index 5f57e3615..5f11ef3a6 100644
> --- a/libdtrace/dt_program.h
> +++ b/libdtrace/dt_program.h
> @@ -28,6 +28,9 @@ struct dtrace_prog {
>  	uint8_t dp_dofversion;	/* DOF version this program requires */
>  };
>  
> +extern int dt_stmt_clsflag_set(dtrace_stmtdesc_t *stp, int flags);
> +extern int dt_stmt_clsflag_test(dtrace_stmtdesc_t *stp, int flags);
> +
>  extern dtrace_prog_t *dt_program_create(dtrace_hdl_t *);
>  extern void dt_program_destroy(dtrace_hdl_t *, dtrace_prog_t *);
>  
> diff --git a/libdtrace/dt_prov_uprobe.c b/libdtrace/dt_prov_uprobe.c
> index 11ff01051..9ca190b72 100644
> --- a/libdtrace/dt_prov_uprobe.c
> +++ b/libdtrace/dt_prov_uprobe.c
> @@ -27,6 +27,7 @@
>   */
>  #include <sys/types.h>
>  #include <assert.h>
> +#include <ctype.h>
>  #include <errno.h>
>  #include <string.h>
>  
> @@ -37,6 +38,7 @@
>  #include "dt_list.h"
>  #include "dt_provider_tp.h"
>  #include "dt_probe.h"
> +#include "dt_program.h"
>  #include "dt_pid.h"
>  #include "dt_string.h"
>  #include "port.h"
> @@ -270,7 +272,53 @@ clean_usdt_probes(dtrace_hdl_t *dtp)
>  static int
>  ignore_clause(dtrace_hdl_t *dtp, int n, const dt_probe_t *uprp)
>  {
> -	/* To be safe, ignore nothing. */
> +	dtrace_stmtdesc_t	*stp = dtp->dt_stmts[n];
> +	dtrace_probedesc_t	*pdp = &stp->dtsd_ecbdesc->dted_probe;
> +
> +	/*
> +	 * Some clauses could never be called for a USDT probe,
> +	 * regardless of the underlying probe uprp.  Cache this
> +	 * status in the clause flags for dt_stmts[n].
> +	 */
> +	if (dt_stmt_clsflag_test(stp, DT_CLSFLAG_USDT_INCLUDE | DT_CLSFLAG_USDT_EXCLUDE) == 0) {
> +		char lastchar = pdp->prv[strlen(pdp->prv) - 1];
> +
> +		/*
> +		 * If the last char in the provider description is
> +		 * neither '*' nor a digit, it cannot be a USDT probe.
> +		 */
> +		if (lastchar != '*' && !isdigit(lastchar)) {
> +			dt_stmt_clsflag_set(stp, DT_CLSFLAG_USDT_EXCLUDE);
> +			return 1;
> +		}
> +
> +		/*
> +		 * If the provider description is "pid[0-9]*", it
> +		 * is a pid probe, not USDT.
> +		 */
> +		if (strncmp(pdp->prv, "pid", 3) == 0) {
> +			int i, l = strlen(pdp->prv);
> +
> +			for (i = 3; i < l; i++)
> +				if (!isdigit((pdp->prv[i])))
> +					break;
> +
> +			if (i == l) {
> +				dt_stmt_clsflag_set(stp, DT_CLSFLAG_USDT_EXCLUDE);
> +				return 1;
> +			}
> +		}
> +
> +		/* Otherwise, it is possibly a USDT probe. */
> +		dt_stmt_clsflag_set(stp, DT_CLSFLAG_USDT_INCLUDE);
> +	}
> +	if (dt_stmt_clsflag_test(stp, DT_CLSFLAG_USDT_EXCLUDE) == 1)
> +		return 1;
> +
> +	/*
> +	 * If we cannot ignore this statement, try to use uprp.
> +	 */
> +
>  	return 0;
>  }
>  
> @@ -453,7 +501,8 @@ static int discover(dtrace_hdl_t *dtp)
>  		stp = dtp->dt_stmts[i];
>  		if (stp == NULL)
>  			continue;
> -		dt_pid_create_usdt_probes(&stp->dtsd_ecbdesc->dted_probe, dtp, &pcb);
> +		if (dt_stmt_clsflag_test(stp, DT_CLSFLAG_USDT_EXCLUDE) != 1)
> +			dt_pid_create_usdt_probes(&stp->dtsd_ecbdesc->dted_probe, dtp, &pcb);
>  	}
>  
>  	return 0;
> diff --git a/libdtrace/dtrace.h b/libdtrace/dtrace.h
> index e636c5065..20672d3fc 100644
> --- a/libdtrace/dtrace.h
> +++ b/libdtrace/dtrace.h
> @@ -161,6 +161,8 @@ typedef struct dtrace_stmtdesc {
>  #define DT_CLSFLAG_EXIT			16	/* exit */
>  #define DT_CLSFLAG_DESTRUCT		32	/* destructive */
>  #define DT_CLSFLAG_AGGREGATION		64	/* aggregation */
> +#define DT_CLSFLAG_USDT_INCLUDE		128	/* could be used in USDT clause */
> +#define DT_CLSFLAG_USDT_EXCLUDE		256	/* could not be used in USDT clause */
>  
>  typedef int dtrace_stmt_f(dtrace_hdl_t *dtp, dtrace_prog_t *pgp,
>      dtrace_stmtdesc_t *sdp, void *data);
> -- 
> 2.43.5
>