From 71fa3d0011cc19236de082ae068ed2306774e91a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Sun, 20 Feb 2011 10:38:17 +0100
Subject: Refactor building of the exception stacktrace

As a preparation for providing information about the source
location for an MFA item in an exception stacktrace, refactor
the code that builds the exception stacktrace. Basically we
need two passes over the saved continuation counters: a first
pass to calculate the needed heap space and a second pass to
actually build the stacktrace.
---
 erts/emulator/beam/beam_emu.c | 89 +++++++++++++++++++++----------------------
 1 file changed, 43 insertions(+), 46 deletions(-)

(limited to 'erts/emulator/beam/beam_emu.c')

diff --git a/erts/emulator/beam/beam_emu.c b/erts/emulator/beam/beam_emu.c
index 0bd5e27843..3c323634b7 100644
--- a/erts/emulator/beam/beam_emu.c
+++ b/erts/emulator/beam/beam_emu.c
@@ -5903,9 +5903,14 @@ build_stacktrace(Process* c_p, Eterm exc) {
     struct StackTrace* s;
     Eterm  args;
     int    depth;
-    BeamInstr* current;
-    Eterm  Where = NIL;
-    Eterm *next_p = &Where;
+    FunctionInfo fi;
+    FunctionInfo* stk;
+    FunctionInfo* stkp;
+    Eterm res = NIL;
+    Uint heap_size;
+    Eterm* hp;
+    Eterm mfa;
+    int i;
 
     if (! (s = get_trace_from_exc(exc))) {
         return NIL;
@@ -5924,64 +5929,56 @@ build_stacktrace(Process* c_p, Eterm exc) {
      * saved s->current should already contain the proper value.
      */
     if (s->pc != NULL) {
-	current = find_function_from_pc(s->pc);
+	erts_lookup_function_info(&fi, s->pc, 1);
+    } else if (GET_EXC_INDEX(s->freason) ==
+	       GET_EXC_INDEX(EXC_FUNCTION_CLAUSE)) {
+	erts_lookup_function_info(&fi, s->current, 1);
     } else {
-	current = s->current;
+	erts_set_current_function(&fi, s->current);
     }
+
     /*
-     * If current is still NULL, default to the initial function
+     * If fi.current is still NULL, default to the initial function
      * (e.g. spawn_link(erlang, abs, [1])).
      */
-    if (current == NULL) {
-	current = c_p->initial;
+    if (fi.current == NULL) {
+	erts_set_current_function(&fi, c_p->initial);
 	args = am_true; /* Just in case */
     } else {
 	args = get_args_from_exc(exc);
     }
 
-    depth = s->depth;
-    
     /*
-     * Add the {M,F,A} for the current function 
-     * (where A is arity or [Argument]).
+     * Look up all saved continuation pointers and calculate
+     * needed heap space.
      */
-    {
-	int i;
-	Eterm mfa;
-	Uint heap_size = 7*(depth+1);
-	Eterm* hp = HAlloc(c_p, heap_size);
-	Eterm* hp_end = hp + heap_size;
-
-	if (args != am_true) {
-	    /* We have an arglist - use it */
-	    mfa = TUPLE4(hp, current[0], current[1], args, NIL);
-	} else {
-	    Eterm arity = make_small(current[2]);
-	    mfa = TUPLE4(hp, current[0], current[1], arity, NIL);
+    depth = s->depth;
+    stk = stkp = (FunctionInfo *) erts_alloc(ERTS_ALC_T_TMP,
+				      depth*sizeof(FunctionInfo));
+    heap_size = fi.needed + 2;
+    for (i = 0; i < depth; i++) {
+	erts_lookup_function_info(stkp, s->trace[i], 1);
+	if (stkp->current) {
+	    heap_size += stkp->needed + 2;
+	    stkp++;
 	}
-	hp += 5;
-	ASSERT(*next_p == NIL);
-	*next_p = CONS(hp, mfa, NIL);
-	next_p = &CDR(list_val(*next_p));
-	hp += 2;
+    }
 
-	/* 
-	 * Finally, we go through the saved continuation pointers.
-	 */
-	for (i = 0; i < depth; i++) {
-	    BeamInstr *fi = find_function_from_pc((BeamInstr *) s->trace[i]);
-	    if (fi == NULL) continue;
-	    mfa = TUPLE4(hp, fi[0], fi[1], make_small(fi[2]), NIL);
-	    hp += 5;
-	    ASSERT(*next_p == NIL);
-	    *next_p = CONS(hp, mfa, NIL);
-	    next_p = &CDR(list_val(*next_p));
-	    hp += 2;
-	}
-	ASSERT(hp <= hp_end);
-	HRelease(c_p, hp_end, hp);
+    /*
+     * Allocate heap space and build the stacktrace.
+     */
+    hp = HAlloc(c_p, heap_size);
+    while (stkp > stk) {
+	stkp--;
+	hp = erts_build_mfa_item(stkp, hp, am_true, &mfa);
+	res = CONS(hp, mfa, res);
+	hp += 2;
     }
-    return Where;
+    hp = erts_build_mfa_item(&fi, hp, args, &mfa);
+    res = CONS(hp, mfa, res);
+
+    erts_free(ERTS_ALC_T_TMP, (void *) stk);
+    return res;
 }
 
 
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