Hi,
A bt(5) exit() statement causes the btrace(8) interpreter to exit(3)
immediately.
A BPFtrace exit() statement is more nuanced: the END probe is executed
and the contents of all maps are printed before the interpreter exits.
This patch adds a halting check after the execution of each bt(5)
statement. If a statement causes the program to halt, the halt
bubbles up to the top-level rule evaluation loop and terminates
execution. rules_teardown() then runs, just as if the program had
received SIGTERM.
Two edge-like cases:
1. You can exit() from BEGIN. rules_setup() returns non-zero if this
happens so the main loop knows to halt immediately.
2. You can exit() from END. This is just an early-return: the END probe
doesn't run again.
Thoughts?
$ btrace -e '
BEGIN {
@[probe] = "reached";
exit();
@[probe] = "not reached";
}
END {
@[probe] = "reached";
exit();
@[probe] = "not reached";
}'
Index: btrace.c
===================================================================
RCS file: /cvs/src/usr.sbin/btrace/btrace.c,v
retrieving revision 1.79
diff -u -p -r1.79 btrace.c
--- btrace.c 12 Oct 2023 15:16:44 -0000 1.79
+++ btrace.c 18 Oct 2023 17:54:16 -0000
@@ -71,10 +71,10 @@ struct dtioc_probe_info *dtpi_get_by_val
* Main loop and rule evaluation.
*/
void rules_do(int);
-void rules_setup(int);
-void rules_apply(int, struct dt_evt *);
+int rules_setup(int);
+int rules_apply(int, struct dt_evt *);
void rules_teardown(int);
-void rule_eval(struct bt_rule *, struct dt_evt *);
+int rule_eval(struct bt_rule *, struct dt_evt *);
void rule_printmaps(struct bt_rule *);
/*
@@ -84,7 +84,7 @@ uint64_t builtin_nsecs(struct dt_evt *
const char *builtin_kstack(struct dt_evt *);
const char *builtin_arg(struct dt_evt *, enum bt_argtype);
struct bt_arg *fn_str(struct bt_arg *, struct dt_evt *, char *);
-void stmt_eval(struct bt_stmt *, struct dt_evt *);
+int stmt_eval(struct bt_stmt *, struct dt_evt *);
void stmt_bucketize(struct bt_stmt *, struct dt_evt *);
void stmt_clear(struct bt_stmt *);
void stmt_delete(struct bt_stmt *, struct dt_evt *);
@@ -405,6 +405,7 @@ void
rules_do(int fd)
{
struct sigaction sa;
+ int halt = 0;
memset(&sa, 0, sizeof(sa));
sigemptyset(&sa.sa_mask);
@@ -415,9 +416,9 @@ rules_do(int fd)
if (sigaction(SIGTERM, &sa, NULL))
err(1, "sigaction");
- rules_setup(fd);
+ halt = rules_setup(fd);
- while (!quit_pending && g_nprobes > 0) {
+ while (!quit_pending && !halt && g_nprobes > 0) {
static struct dt_evt devtbuf[64];
ssize_t rlen;
size_t i;
@@ -434,8 +435,11 @@ rules_do(int fd)
if ((rlen % sizeof(struct dt_evt)) != 0)
err(1, "incorrect read");
- for (i = 0; i < rlen / sizeof(struct dt_evt); i++)
- rules_apply(fd, &devtbuf[i]);
+ for (i = 0; i < rlen / sizeof(struct dt_evt); i++) {
+ halt = rules_apply(fd, &devtbuf[i]);
+ if (halt)
+ break;
+ }
}
rules_teardown(fd);
@@ -484,7 +488,7 @@ rules_action_scan(struct bt_stmt *bs)
return evtflags;
}
-void
+int
rules_setup(int fd)
{
struct dtioc_probe_info *dtpi;
@@ -493,7 +497,7 @@ rules_setup(int fd)
struct bt_probe *bp;
struct bt_stmt *bs;
struct bt_arg *ba;
- int dokstack = 0, on = 1;
+ int dokstack = 0, halt = 0, on = 1;
uint64_t evtflags;
TAILQ_FOREACH(r, &g_rules, br_next) {
@@ -553,7 +557,7 @@ rules_setup(int fd)
clock_gettime(CLOCK_REALTIME, &bt_devt.dtev_tsp);
if (rbegin)
- rule_eval(rbegin, &bt_devt);
+ halt = rule_eval(rbegin, &bt_devt);
/* Enable all probes */
TAILQ_FOREACH(r, &g_rules, br_next) {
@@ -571,9 +575,14 @@ rules_setup(int fd)
if (ioctl(fd, DTIOCRECORD, &on))
err(1, "DTIOCRECORD");
}
+
+ return halt;
}
-void
+/*
+ * Returns non-zero if the program should halt.
+ */
+int
rules_apply(int fd, struct dt_evt *dtev)
{
struct bt_rule *r;
@@ -586,9 +595,11 @@ rules_apply(int fd, struct dt_evt *dtev)
continue;
dtai_cache(fd, &dt_dtpis[dtev->dtev_pbn - 1]);
- rule_eval(r, dtev);
+ if (rule_eval(r, dtev))
+ return 1;
}
}
+ return 0;
}
void
@@ -637,7 +648,10 @@ rules_teardown(int fd)
rule_printmaps(r);
}
-void
+/*
+ * Returns non-zero if the program should halt.
+ */
+int
rule_eval(struct bt_rule *r, struct dt_evt *dtev)
{
struct bt_stmt *bs;
@@ -651,7 +665,7 @@ rule_eval(struct bt_rule *r, struct dt_e
if (r->br_filter != NULL && r->br_filter->bf_condition != NULL) {
if (stmt_test(r->br_filter->bf_condition, dtev) == false) {
bt_filtered++;
- return;
+ return 0;
}
}
@@ -660,15 +674,19 @@ rule_eval(struct bt_rule *r, struct dt_e
struct bt_stmt *bbs = (struct bt_stmt *)bs->bs_var;
while (bbs != NULL) {
- stmt_eval(bbs, dtev);
+ if (stmt_eval(bbs, dtev))
+ return 1;
bbs = SLIST_NEXT(bbs, bs_next);
}
continue;
}
- stmt_eval(bs, dtev);
+ if (stmt_eval(bs, dtev))
+ return 1;
}
+
+ return 0;
}
void
@@ -802,9 +820,14 @@ builtin_arg(struct dt_evt *dtev, enum bt
return buf;
}
-void
+/*
+ * Returns non-zero if the program should halt.
+ */
+int
stmt_eval(struct bt_stmt *bs, struct dt_evt *dtev)
{
+ int halt = 0;
+
switch (bs->bs_act) {
case B_AC_BUCKETIZE:
stmt_bucketize(bs, dtev);
@@ -816,7 +839,7 @@ stmt_eval(struct bt_stmt *bs, struct dt_
stmt_delete(bs, dtev);
break;
case B_AC_EXIT:
- exit(0);
+ halt = 1;
break;
case B_AC_INSERT:
stmt_insert(bs, dtev);
@@ -842,6 +865,7 @@ stmt_eval(struct bt_stmt *bs, struct dt_
default:
xabort("no handler for action type %d", bs->bs_act);
}
+ return halt;
}
/*
Index: bt.5
===================================================================
RCS file: /cvs/src/usr.sbin/btrace/bt.5,v
retrieving revision 1.16
diff -u -p -r1.16 bt.5
--- bt.5 30 Jun 2023 13:31:37 -0000 1.16
+++ bt.5 18 Oct 2023 17:54:16 -0000
@@ -127,6 +127,11 @@ from
.Va @map .
.It Fn exit
Terminate execution with exit code 0.
+The
+.Ic END
+probe,
+if any,
+is executed and the contents of all maps are printed.
.It Fn hist "value"
Increment the bucket corresponding to
.Va value
