bc: fix for() to not leave data on stack

function                                             old     new   delta
zbc_parse_stmt_possibly_auto                        1665    1697     +32
zbc_vm_process                                       672     701     +29
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 61/0)               Total: 61 bytes
   text	   data	    bss	    dec	    hex	filename
 981656	    485	   7296	 989437	  f18fd	busybox_old
 981748	    485	   7296	 989529	  f1959	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 38 insertions, 25 deletions

diff --git a/miscutils/bc.c b/miscutils/bc.c
index 50e5457b9..441cb0467 100644
--- a/miscutils/bc.c
+++ b/miscutils/bc.c
@@ -170,6 +170,8 @@
 #define DEBUG_LEXER   0
 #define DEBUG_COMPILE 0
 #define DEBUG_EXEC    0
+// This can be left enabled for production as well:
+#define SANITY_CHECKS 1
 
 #if DEBUG_LEXER
 static uint8_t lex_indent;
@@ -1218,8 +1220,6 @@ static char** bc_program_const(size_t idx)
         IF_DC(return bc_vec_item(&G.prog.consts, idx);)
 }
 
-
-
 static int bc_id_cmp(const void *e1, const void *e2)
 {
         return strcmp(((const BcId *) e1)->name, ((const BcId *) e2)->name);
@@ -4227,12 +4227,15 @@ static BC_STATUS zbc_parse_for(BcParse *p)
         s = zbc_lex_next(&p->l);
         if (s) RETURN_STATUS(s);
 
-        if (p->l.t.t != BC_LEX_SCOLON)
+        if (p->l.t.t != BC_LEX_SCOLON) {
                 s = zbc_parse_expr(p, 0);
-        else
+                bc_parse_push(p, BC_INST_POP);
+                if (s) RETURN_STATUS(s);
+        } else {
                 s = bc_POSIX_does_not_allow_empty_X_expression_in_for("init");
+                IF_ERROR_RETURN_POSSIBLE(if (s) RETURN_STATUS(s);)
+        }
 
-        if (s) RETURN_STATUS(s);
         if (p->l.t.t != BC_LEX_SCOLON) RETURN_STATUS(bc_error_bad_token());
         s = zbc_lex_next(&p->l);
         if (s) RETURN_STATUS(s);
@@ -4254,8 +4257,8 @@ static BC_STATUS zbc_parse_for(BcParse *p)
                 bc_parse_pushNUM(p);
                 s = bc_POSIX_does_not_allow_empty_X_expression_in_for("condition");
         }
-
         if (s) RETURN_STATUS(s);
+
         if (p->l.t.t != BC_LEX_SCOLON) RETURN_STATUS(bc_error_bad_token());
 
         s = zbc_lex_next(&p->l);
@@ -4267,12 +4270,14 @@ static BC_STATUS zbc_parse_for(BcParse *p)
         bc_vec_push(&p->conds, &update_idx);
         bc_vec_push(&p->func->labels, &p->func->code.len);
 
-        if (p->l.t.t != BC_LEX_RPAREN)
+        if (p->l.t.t != BC_LEX_RPAREN) {
                 s = zbc_parse_expr(p, 0);
-        else
+                bc_parse_push(p, BC_INST_POP);
+                if (s) RETURN_STATUS(s);
+        } else {
                 s = bc_POSIX_does_not_allow_empty_X_expression_in_for("update");
-
-        if (s) RETURN_STATUS(s);
+                IF_ERROR_RETURN_POSSIBLE(if (s) RETURN_STATUS(s);)
+        }
 
         if (p->l.t.t != BC_LEX_RPAREN) RETURN_STATUS(bc_error_bad_token());
         bc_parse_pushJUMP(p, cond_idx);
@@ -6434,12 +6439,13 @@ static BC_STATUS zbc_program_exec(void)
         BcFunc *func = bc_program_func(ip->func);
         char *code = func->code.v;
 
-        dbg_exec("func:%zd bytes:%zd ip:%zd", ip->func, func->code.len, ip->idx);
+        dbg_exec("func:%zd bytes:%zd ip:%zd results.len:%d",
+                        ip->func, func->code.len, ip->idx, G.prog.results.len);
         while (ip->idx < func->code.len) {
                 BcStatus s = BC_STATUS_SUCCESS;
                 char inst = code[ip->idx++];
 
-                dbg_exec("inst at %zd:%d", ip->idx - 1, inst);
+                dbg_exec("inst at %zd:%d results.len:%d", ip->idx - 1, inst, G.prog.results.len);
                 switch (inst) {
 #if ENABLE_BC
                         case BC_INST_JUMP_ZERO: {
@@ -6671,7 +6677,6 @@ static BC_STATUS zbc_program_exec(void)
                 }
 
                 fflush_and_check();
-
         }
 
         RETURN_STATUS(BC_STATUS_SUCCESS);
@@ -6723,23 +6728,16 @@ static BC_STATUS zbc_vm_process(const char *text)
                 // storage.
                 if (IS_BC) {
                         BcFunc *f;
-                        BcInstPtr *ip;
-
-                        //FIXME: this does not clear up the stack
-                        //for(i=1; i<3; i++) {
-                        //    i
-                        //    if(i==2) continue
-                        //    77
-                        //}
-//                      if (G.prog.results.len != 0)
-//                              bb_error_msg_and_die("data stack not empty: %d slots", G.prog.results.len);
+                        BcInstPtr *ip = (void*)G.prog.exestack.v;
 
+#if SANITY_CHECKS
+                        if (G.prog.results.len != 0)
+                                bb_error_msg_and_die("data stack not empty: %d slots", G.prog.results.len);
                         if (G.prog.exestack.len != 1) // should be empty
                                 bb_error_msg_and_die("BUG:call stack");
-
-                        ip = (void*)G.prog.exestack.v;
                         if (ip->func != BC_PROG_MAIN)
                                 bb_error_msg_and_die("BUG:not MAIN");
+#endif
 //bb_error_msg("ip->func:%d >idx:%d >len:%d", ip->func, ip->idx, ip->len);
                         f = bc_program_func_BC_PROG_MAIN();
 //bb_error_msg("MAIN->code.len:%d >strs.len:%d >consts.len:%d", f->code.len, f->strs.len, f->consts.len); // labels, autos, nparams
diff --git a/testsuite/bc.tests b/testsuite/bc.tests
index edff209bb..b3ce894ee 100755
--- a/testsuite/bc.tests
+++ b/testsuite/bc.tests
@@ -56,6 +56,21 @@ testing "bc for(;;)" \
         "2\n3\n2\n9\n" \
         "" "i=2; for (;;) { 2; if(--i==0) break; 3; }; 9"
 
+testing "bc for (;cond;)" \
+        "bc" \
+        "1\n2\n3\n9\n" \
+        "" "i=0; for(;i<3;)++i; 9"
+
+testing "bc for (;cond;upd)" \
+        "bc" \
+        "1\n2\n3\n9\n" \
+        "" "i=1; for(;i<4;i++)i; 9"
+
+testing "bc for (init;cond;upd)" \
+        "bc" \
+        "1\n2\n3\n9\n" \
+        "" "for(i=1;i<4;i++)i; 9"
+
 testing "bc define auto" \
         "bc" \
         "8\n9\n" \