From: Christian Ludwig <christian_ludwig@genua.de>
Subject: btrace: Implement else-branch for if-statements in bt(5)
To: <tech@openbsd.org>
Cc: Martin Pieuchot <mpi@openbsd.org>
Date: Wed, 13 Mar 2024 13:45:32 +0100

Hi,

btrace has support for if-statements already implemented, but it lacks
support for an else-branch. This diff implements that, including
'else if'.

Although it has a regress test attached, it certainly needs more
testing.

Is the abuse of a struct bt_arg as container for the two statement
lists acceptable, or do we want a proper type?

So long,


 - Christian

---
 regress/usr.sbin/btrace/if.bt |  8 ++++++++
 regress/usr.sbin/btrace/if.ok |  1 +
 usr.sbin/btrace/bt_parse.y    | 15 ++++++++++-----
 usr.sbin/btrace/btrace.c      | 14 +++++++++++---
 4 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/regress/usr.sbin/btrace/if.bt b/regress/usr.sbin/btrace/if.bt
index 053801cac54..89cdc3f9f47 100644
--- a/regress/usr.sbin/btrace/if.bt
+++ b/regress/usr.sbin/btrace/if.bt
@@ -1,6 +1,8 @@
 BEGIN {
 	if (0)
 		printf("nothing");
+	else
+		printf("printed!\n");
 
 	@var = 0;
 	if (@var)
@@ -8,10 +10,16 @@ BEGIN {
 
 	if (1) {
 		printf("printed!\n");
+	} else if (1) {
+		printf("not printed\n");
+	} else {
+		printf("not printed\n");
 	}
 }
 
 END {
+	if (1) { ; } else printf("not printed\n");
+
 	if (42) {
 		printf("multiple ");
 		@var = 4;
diff --git a/regress/usr.sbin/btrace/if.ok b/regress/usr.sbin/btrace/if.ok
index c2d5a91bc90..7b26ae9cd7c 100644
--- a/regress/usr.sbin/btrace/if.ok
+++ b/regress/usr.sbin/btrace/if.ok
@@ -1,2 +1,3 @@
 printed!
+printed!
 multiple (4) statements
diff --git a/usr.sbin/btrace/bt_parse.y b/usr.sbin/btrace/bt_parse.y
index 075eaa5b7f8..19b3e5029c6 100644
--- a/usr.sbin/btrace/bt_parse.y
+++ b/usr.sbin/btrace/bt_parse.y
@@ -119,7 +119,7 @@ static int 	 beflag = 0;		/* BEGIN/END parsing context flag */
 %token	<v.i>		ERROR ENDFILT
 %token	<v.i>		OP_EQ OP_NE OP_LE OP_LT OP_GE OP_GT OP_LAND OP_LOR
 /* Builtins */
-%token	<v.i>		BUILTIN BEGIN END HZ IF STR
+%token	<v.i>		BUILTIN BEGIN ELSE END HZ IF STR
 /* Functions and Map operators */
 %token  <v.i>		F_DELETE F_PRINT
 %token	<v.i>		MFUNC FUNC0 FUNC1 FUNCN OP1 OP2 OP4 MOP0 MOP1
@@ -248,7 +248,9 @@ stmt	: ';' NL			{ $$ = NULL; }
 	| GVAR '=' OP4 '(' expr ',' vargs ')'	{ $$ = bh_inc($1, $5, $7); }
 	;
 
-stmtblck: IF '(' expr ')' block			{ $$ = bt_new($3, $5); }
+stmtblck: IF '(' expr ')' block			{ $$ = bt_new($3, $5, NULL); }
+	| IF '(' expr ')' block ELSE block	{ $$ = bt_new($3, $5, $7); }
+	| IF '(' expr ')' block ELSE stmtblck	{ $$ = bt_new($3, $5, $7); }
 	;
 
 stmtlist: stmtlist stmtblck		{ $$ = bs_append($1, $2); }
@@ -340,13 +342,15 @@ bc_new(struct bt_arg *term, enum bt_argtype op, struct bt_arg *ba)
 
 /* Create a new if/else test */
 struct bt_stmt *
-bt_new(struct bt_arg *ba, struct bt_stmt *condbs)
+bt_new(struct bt_arg *ba, struct bt_stmt *condbs, struct bt_stmt *elsebs)
 {
-	struct bt_arg *bop;
+	struct bt_arg *bop, *lnk;
 
 	bop = ba_op(B_AT_OP_NE, NULL, ba);
+	lnk = ba_new(condbs, 0);
+	lnk->ba_key = (struct bt_arg *)elsebs;
 
-	return bs_new(B_AC_TEST, bop, (struct bt_var *)condbs);
+	return bs_new(B_AC_TEST, bop, (struct bt_var *)lnk);
 
 }
 /* Create a new probe */
@@ -714,6 +718,7 @@ lookup(char *s)
 		{ "count",	MOP0, 		B_AT_MF_COUNT },
 		{ "cpu",	BUILTIN,	B_AT_BI_CPU },
 		{ "delete",	F_DELETE,	B_AC_DELETE },
+		{ "else",	ELSE,		0 },
 		{ "exit",	FUNC0,		B_AC_EXIT },
 		{ "hist",	OP1,		0 },
 		{ "hz",		HZ,		0 },
diff --git a/usr.sbin/btrace/btrace.c b/usr.sbin/btrace/btrace.c
index ce32989be91..ba3efb2983a 100644
--- a/usr.sbin/btrace/btrace.c
+++ b/usr.sbin/btrace/btrace.c
@@ -474,8 +474,11 @@ rules_action_scan(struct bt_stmt *bs)
 			evtflags |= ba2dtflags(ba);
 			break;
 		case B_AC_TEST:
+			ba = (struct bt_arg *)bs->bs_var;
 			evtflags |= rules_action_scan(
-			    (struct bt_stmt *)bs->bs_var);
+			    (struct bt_stmt *)ba->ba_value);
+			evtflags |= rules_action_scan(
+			    (struct bt_stmt *)ba->ba_key);
 			break;
 		default:
 			break;
@@ -669,8 +672,13 @@ rule_eval(struct bt_rule *r, struct dt_evt *dtev)
 	}
 
 	SLIST_FOREACH(bs, &r->br_action, bs_next) {
-		if ((bs->bs_act == B_AC_TEST) && stmt_test(bs, dtev) == true) {
-			struct bt_stmt *bbs = (struct bt_stmt *)bs->bs_var;
+		if (bs->bs_act == B_AC_TEST) {
+			struct bt_arg *lnk = (struct bt_arg *)bs->bs_var;
+			struct bt_stmt *bbs;
+			if (stmt_test(bs, dtev) == true)
+				bbs = (struct bt_stmt *)lnk->ba_value;
+			else
+				bbs = (struct bt_stmt *)lnk->ba_key;
 
 			while (bbs != NULL) {
 				if (stmt_eval(bbs, dtev))
-- 
2.34.1