From 3ccc4730e54f0f9e86bf96360b7600ab8c9e1d47 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 31 Mar 2011 07:22:02 +0200
Subject: Rewrite stack handling

Problems with the current stack implementation:

* The GUI assumes that the stack frame pushed on the stack
is level 2. If the 'no_tail' option is set for the process,
there may not be an entry for level 2.

* In each stack entry, the line number is the line number of
the caller, not the line number for the function in the 'mfa'
field as might be expected. That complicates generation of
a stacktrace with line number information.

Change the implementation as follows:

* Keep the information for the current function (its MFA and
current line number) in the #ieval{} record. Don't push it
onto the stack. Only push the information when another function
is called. That will ensure that the MFA and the line number
is found in the same stack entry. That also has the advantage
that if the 'no_tail' option is set, the stack not need to
be modified for tail-recursive calls.

* Make sure that there always is an entry for level two.
---
 lib/debugger/src/dbg_istk.erl | 49 ++++++++++++++++++++++++-------------------
 1 file changed, 27 insertions(+), 22 deletions(-)

(limited to 'lib/debugger/src/dbg_istk.erl')

diff --git a/lib/debugger/src/dbg_istk.erl b/lib/debugger/src/dbg_istk.erl
index b852e1f8fd..2e7b114fab 100644
--- a/lib/debugger/src/dbg_istk.erl
+++ b/lib/debugger/src/dbg_istk.erl
@@ -18,9 +18,9 @@
 %%
 -module(dbg_istk).
 -export([init/0,to_external/0,from_external/1,
-	 push/3,pop/0,pop/1,stack_level/0,
+	 push/2,pop/0,pop/1,stack_level/0,
 	 exception_stacktrace/2,
-	 bindings/1,stack_frame/2,backtrace/1,
+	 bindings/1,stack_frame/2,backtrace/2,
 	 in_use_p/2]).
 
 -include("dbg_ieval.hrl").
@@ -30,7 +30,6 @@
 -record(e,
 	{level,					%Level
 	 mfa,					%{Mod,Func,Args|Arity}|{Fun,Args}
-	 cm,					%Module called from
 	 line,					%Line called from
 	 bindings
 	 }).
@@ -61,17 +60,17 @@ init(Stack) ->
 %%   false - nothing is pushed
 %% Whenever a function returns, the corresponding call frame is popped.
 
-push(MFA, Bs, #ieval{level=Le,module=Cm,line=Li,top=Lc}) ->
-    Entry = #e{level=Le,mfa=MFA,cm=Cm,line=Li,bindings=Bs},
+push(Bs, #ieval{level=Le,module=Mod,function=Name,arguments=As,
+		line=Li,top=Lc}=Ieval) ->
+    Entry = #e{level=Le,mfa={Mod,Name,As},line=Li,bindings=Bs},
     case get(trace_stack) of
-	false -> ignore;
+	false ->
+	    Ieval#ieval{level=Le+1};
 	no_tail when Lc ->
-	    case get(?STACK) of
-		[] -> put(?STACK, [Entry]);
-		[_Entry|Entries] -> put(?STACK, [Entry|Entries])
-	    end;
+	    Ieval;
 	_ -> % all | no_tail when Lc =:= false
-	    put(?STACK, [Entry|get(?STACK)])
+	    put(?STACK, [Entry|get(?STACK)]),
+	    Ieval#ieval{level=Le+1}
     end.
 
 pop() ->
@@ -117,13 +116,15 @@ stack_level([#e{level=Le}|_]) -> Le.
 %% function and convert argument lists to arity for all but the topmost
 %% entry (and funs).
 
-exception_stacktrace(complete, #ieval{}) ->
-    fix_stacktrace(1);
+exception_stacktrace(complete, #ieval{}=Ieval) ->
+    #ieval{module=Mod,function=Name,arguments=As} = Ieval,
+    Stk = [#e{mfa={Mod,Name,As}}|get(?STACK)],
+    fix_stacktrace(Stk);
 exception_stacktrace(no_current, #ieval{}) ->
-    fix_stacktrace(2).
+    fix_stacktrace(get(?STACK)).
 
-fix_stacktrace(Start) ->
-    case fix_stacktrace2(sublist(get(?STACK), Start, 3)) of
+fix_stacktrace(Stk) ->
+    case fix_stacktrace2(sublist(Stk, 1, 3)) of
 	[] ->
 	    [];
 	[H|T] ->
@@ -180,13 +181,15 @@ stack_frame(up, SP) ->
 stack_frame(down, SP) ->
     stack_frame(SP, down, lists:reverse(get(?STACK))).
 
-stack_frame(SP, up, [#e{level=Le,cm=Cm,line=Li,bindings=Bs}|_]) when Le < SP ->
+stack_frame(SP, up, [#e{level=Le,mfa={Cm,_,_},line=Li,bindings=Bs}|_])
+  when Le < SP ->
     {Le,{Cm,Li},Bs};
-stack_frame(SP, down, [#e{level=Le,cm=Cm,line=Li,bindings=Bs}|_]) when Le > SP ->
+stack_frame(SP, down, [#e{level=Le,mfa={Cm,_,_},line=Li,bindings=Bs}|_])
+  when Le > SP ->
     {Le,{Cm,Li},Bs};
 stack_frame(SP, Dir, [#e{level=SP}|Stack]) ->
     case Stack of
-	[#e{level=Le,cm=Cm,line=Li,bindings=Bs}|_] ->
+	[#e{level=Le,mfa={Cm,_,_},line=Li,bindings=Bs}|_] ->
 	    {Le,{Cm,Li},Bs};
 	[] when Dir =:= up ->
 	    top;
@@ -200,10 +203,12 @@ stack_frame(SP, Dir, [_Entry|Stack]) ->
 %%   HowMany = all | int()
 %%   Backtrace = {Le, MFA}
 %% Return all/the last N called functions, in reversed call order
-backtrace(HowMany) ->
+backtrace(HowMany, Ieval) ->
+    #ieval{level=Level,module=Mod,function=Name,arguments=As} = Ieval,
+    Stack0 = [#e{level=Level,mfa={Mod,Name,As}}|get(?STACK)],
     Stack = case HowMany of
-		all -> get(?STACK);
-		N -> lists:sublist(get(?STACK), N)
+		all -> Stack0;
+		N -> lists:sublist(Stack0, N)
 	    end,
     [{Le,MFA} || #e{level=Le,mfa=MFA} <- Stack].
 
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