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revision 660, Thu Jun 15 04:40:56 2000 UTC revision 675, Fri Jun 23 09:18:18 2000 UTC
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12  Tag: <post-commit CVS tag>  Tag: <post-commit CVS tag>
13  Description:  Description:
14  ----------------------------------------------------------------------  ----------------------------------------------------------------------
15    Name: Matthias Blume
16    Date: 2000/06/23 18:20:00 JST
17    Tag: blume-20000623-btrace
18    Description:
19    
20    This updates adds a backtrace facility to aid programmers in debugging
21    their programs.  This involves the following changes:
22    
23    1. Module system/smlnj/init/core.sml (structure _Core) now has hooks for
24       keeping track of the current call stack.  When programs are compiled
25       in a special mode, the compiler will insert calls to these hooks
26       into the user program.
27       "Hook" means that it is possible for different implementations of
28       back-tracing to register themselves (at different times).
29    
30    2. compiler/MiscUtil/profile/btrace.sml implements the annotation phase
31       as an Absyn.dec->Absyn.dec rewrite.  Normally this phase is turned off.
32       It can be turned on using this call:
33         SMLofNJ.Internals.BTrace.mode (SOME true);
34       Turning it off again:
35         SMLofNJ.Internals.BTrace.mode (SOME false);
36       Querying the current status:
37         SMLofNJ.Internals.BTrace.mode NONE;
38       Annotated programs are about twice as big as normal ones, and they
39       run a factor of 2 to 4 slower with a dummy back-trace plugin (one
40       where all hooks do nothing).  The slowdown with a plugin that is
41       actually useful (such as the one supplied by default) is even greater,
42       but in the case of the default plugin it is still only an constant
43       factor (amortized).
44    
45    3. system/Basis/Implementation/NJ/internals.{sig,sml} have been augmented
46       with a sub-structure BTrace for controlling back-tracing.  In particular,
47       the above-mentioned function "mode" controls whether the annotation
48       phase is invoked by the compiler.  Another important function is
49       "trigger": when called it aborts the current execution and causes
50       the top-level loop to print a full back-trace.
51    
52    4. compiler/MiscUtil/profile/btimp.sml is the current default plugin
53       for back-tracing.  It keeps track of the dynamic call stack and in
54       addition to that it keeps a partial history at each "level" of that
55       stack.  For example, if a tail-calls b, b tail-calls c, and c tail-calls
56       d and b (at separate times, dynamically), then the report will show:
57    
58       GOTO   d
59             /c
60       GOTO  \b
61       CALL   a
62    
63       This shows that there was an initial non-tail call of a, then a
64       tail-call to b or c, looping behavior in a cluster of functions that
65       consist of b and c, and then a goto from that cluster (i.e., either from
66       b or from c) to d.
67    
68       Note that (depending on the user program) the amount of information
69       that the back-trace module has to keep track of at each level is bounded
70       by a constant.  Thus, the whole implementation has the same asymptotical
71       complexity as the original program (both in space and in time).
72    
73    5. compiler/TopLevel/interact/evalloop.sml has been modified to
74       handle the special exception SMLofNJ.Internals.BTrace.BTrace
75       which is raised by the "trigger" function mentioned above.
76    
77    Notes on usage:
78    
79    - Annotated code works well together with unannotated code:
80    Unannotated calls simply do not show up at all in the backtrace.
81    
82    - It is not a good idea to let modules that were annotated during
83    different sessions run at the same time.  This is because the compiler
84    chooses small integers to identify individual functions, and there
85    will be clashes if different modules were compiled in separate sessions.
86    (Nothing will crash, and you will even be told about the clashes, but
87    back-trace information will in general not be useful.)
88    
89    - Back-tracing can be confused by callcc and capture.
90    
91    - The only way of getting a back-trace right now is to explicitly
92    invoke the "trigger" function from your user program.  Eventually, we
93    should make every exception carry back-trace information (if
94    available).  But since this creates more overhead at "raise"-time
95    (similar to the current exnHistory overhead), I have not yet
96    implemented this.  (The implementation will be rather easy.)  With
97    exceptions carrying back-trace information, this facility will be even
98    more useful because users don't need to modify their programs...
99    
100    - While it is possible to compile the compiler with back-trace
101    annotations turned on (I did it to get some confidence in
102    correctness), you must make absolutely sure that core.sml and
103    btimp.sml are compiled WITHOUT annotation!  (core.sml cannot actually
104    be compiled with annotation because there is no core access yet, but
105    if you compile btimp.sml with annotation, then the system will go into
106    an infinite recursion and crash.)
107    Since CM currently does not know about BTrace, the only way to turn
108    annotations on and off for different modules of the compiler is to
109    interrupt CMB.make, change the settings, and re-invoke it.  Of course,
110    this is awkward and clumsy.
111    
112    Sample sessions:
113    
114    Standard ML of New Jersey v110.28.1 [FLINT v1.5], June 5, 2000
115    - SMLofNJ.Internals.BTrace.mode (SOME true);
116    [autoloading]
117    [autoloading done]
118    val it = false : bool
119    - structure X = struct
120    -     fun main n = let
121    -         fun a (x, 0) = d x
122    -           | a (x, n) = b (x, n - 1)
123    -         and b (x, n) = c (x, n)
124    -         and c (x, n) = a (x, n)
125    -         and d x = e (x, 3)
126    -         and e (x, 0) = f x
127    -           | e (x, n) = e (x, n - 1)
128    -         and f 0 = SMLofNJ.Internals.BTrace.trigger ()
129    -           | f n = n * g (n - 1)
130    -         and g n = a (n, 3)
131    -     in
132    -         f n
133    -     end
134    - end;
135    structure X : sig val main : int -> int end
136    - X.main 3;
137    *** BACK-TRACE ***
138    GOTO   stdIn:4.2-13.20: X.main[2].f
139    GOTO-( stdIn:4.2-13.20: X.main[2].e
140    GOTO   stdIn:4.2-13.20: X.main[2].d
141         / stdIn:4.2-13.20: X.main[2].a
142         | stdIn:4.2-13.20: X.main[2].b
143    GOTO-\ stdIn:4.2-13.20: X.main[2].c
144    CALL   stdIn:4.2-13.20: X.main[2].g
145    GOTO   stdIn:4.2-13.20: X.main[2].f
146    GOTO-( stdIn:4.2-13.20: X.main[2].e
147    GOTO   stdIn:4.2-13.20: X.main[2].d
148         / stdIn:4.2-13.20: X.main[2].a
149         | stdIn:4.2-13.20: X.main[2].b
150    GOTO-\ stdIn:4.2-13.20: X.main[2].c
151    CALL   stdIn:4.2-13.20: X.main[2].g
152    GOTO   stdIn:4.2-13.20: X.main[2].f
153    GOTO-( stdIn:4.2-13.20: X.main[2].e
154    GOTO   stdIn:4.2-13.20: X.main[2].d
155         / stdIn:4.2-13.20: X.main[2].a
156         | stdIn:4.2-13.20: X.main[2].b
157    GOTO-\ stdIn:4.2-13.20: X.main[2].c
158    CALL   stdIn:4.2-13.20: X.main[2].g
159    GOTO   stdIn:4.2-13.20: X.main[2].f
160    CALL   stdIn:2.15-17.4: X.main[2]
161    -
162    
163    (Note that because of a FLINt bug the above code currently does not
164    compile without BTrace turned on.)
165    
166    Here is another example, using my modified Tiger compiler:
167    
168    Standard ML of New Jersey v110.28.1 [FLINT v1.5], June 5, 2000
169    - SMLofNJ.Internals.BTrace.mode (SOME true);
170    [autoloading]
171    [autoloading done]
172    val it = false : bool
173    - CM.make "sources.cm";
174    [autoloading]
175    ...
176    [autoloading done]
177    [scanning sources.cm]
178    [parsing (sources.cm):parse.sml]
179    [creating directory CM/SKEL ...]
180    [parsing (sources.cm):tiger.lex.sml]
181    ...
182    [wrote CM/sparc-unix/semant.sml]
183    [compiling (sources.cm):main.sml]
184    [wrote CM/sparc-unix/main.sml]
185    [New bindings added.]
186    val it = true : bool
187    - Main.compile ("../testcases/merge.tig", "foo.out");
188    *** BACK-TRACE ***
189    CALL   lib/semant.sml:99.2-396.21: SemantFun[2].transExp.trvar
190    CALL   lib/semant.sml:99.2-396.21: SemantFun[2].transExp.trexp
191    CALL   lib/semant.sml:289.3-295.22: SemantFun[2].transExp.trexp.check[2]
192    GOTO   lib/semant.sml:289.3-295.22: SemantFun[2].transExp.trexp.check[2]
193    CALL   lib/semant.sml:99.2-396.21: SemantFun[2].transExp.trexp
194    CALL   lib/semant.sml:99.2-396.21: SemantFun[2].transExp.trexp
195    CALL   lib/semant.sml:488.3-505.6: SemantFun[2].transDec.trdec[2].transBody[2]
196         / lib/semant.sml:411.65-543.8: SemantFun[2].transDec
197    CALL-\ lib/semant.sml:413.2-540.9: SemantFun[2].transDec.trdec[2]
198    CALL   lib/semant.sml:99.2-396.21: SemantFun[2].transExp.trexp
199    CALL   lib/semant.sml:8.52-558.4: SemantFun[2].transProg[2]
200    CALL   main.sml:1.18-118.4: Main.compile[2]
201    -
202    
203    ----------------------------------------------------------------------
204    Name: Matthias Blumen
205    Date: 2000/06/21 18:00:00 JST
206    Tag: blume-20000621-manual
207    Description:
208    
209    CM manual update: Path environments documented.
210    
211    ----------------------------------------------------------------------
212    Name: Matthias Blume
213    Date: 2000/06/19 13:40:00
214    Tag: blume-20000619-manual
215    Description:
216    
217    CM manual and system/README update.  This only covers the fact that
218    there are no more implicit anchors.  (Path environments and the "bind"
219    option to "cm" have yet to be documented.)
220    
221    ----------------------------------------------------------------------
222    Name: Matthias Blume
223    Date: 2000/06/19 11:05:00 JST
224    Tag: blume-20000619-chdir-bugfix
225    Description:
226    
227    Fixed a bug in new SrcPath module that sometimes led to a bad chDir call.
228    
229    ----------------------------------------------------------------------
230    Name: Matthias Blume
231    Date: 2000/06/18 22:00:10 JST
232    Tag: blume-20000618-implicit-anchors-really-gone
233    Description:
234    
235    I updates the previous HISTORY entry where I forgot to mention that
236    implicit anchors are no longer with us.
237    
238    The current update also gets rid of the (now useless) controller
239    CM.Control.implicit_anchors.
240    
241    ----------------------------------------------------------------------
242    Name: Matthias Blume
243    Date: 2000/06/16 17:30:00 JST
244    Tag: blume-20000616-anchorenv
245    Description:
246    
247    This patch implements the long anticipated (just kidding :) "anchor
248    environment" mechanism.  In the course of doing this, I also
249    re-implemented CM's internal "SrcPath" module from scratch.  The new
250    one should be more robust in certain boundary cases.  In any case, it
251    is a lot cleaner than its predecessor (IMHO).
252    
253    This time, although there is yet another boot file format change, I
254    kept the unpickler backward-compatible.  As a result, no new bootfiles
255    are necessary and bootstrapping is straightforward.  (You cannot read
256    new bootfiles into an old system, but the other way around is no
257    problem.)
258    
259    Visible changes:
260    
261    ** 0. Implicit path anchors (without the leading $-symbol) are no
262    longer recognized at all. This means that such path names are not
263    illegal either.  For example, the name basis.cm simply refers to a
264    local file called "basis.cm" (i.e, the name is an ordinary path
265    relative to .cm-files directory).  Or, to put it differently, only
266    names that start with $ are anchored paths.
267    
268    ** 1. The $<singlearc> abbreviation for $/<singlearc> has finally
269    vanished.
270    
271    John (Reppy) had critizised this as soon as I originally proposed and
272    implemented it, but at that time I did not really deeply believe
273    him. :) Now I came full-circle because I need the $<singlearc> syntax
274    in another place where it cannot be seen as an abbreviation for
275    $/<singlearc>.  To avoid the confusion, $<singlearc> now means what it
276    seems to mean (i.e., it "expands" into the corresponding anchor
277    value).
278    
279    However, when paths are used as members in CM description files, it
280    continues to be true that there must be at least another arc after the
281    anchor.  This is now enforced separately during semantic analysis
282    (i.e., from a lexical/syntactical point of view, the notation is ok.)
283    
284    ** 2. The "cm" class now accepts an option "bind".  The option's value
285    is a sub-option list of precisely two items -- one labeled "anchor"
286    and the other one labeled "value".  As you might expect, "anchor" is
287    used to specify an anchor name to be bound, and "value" specifies what
288    the anchor is being bound to.
289    
290    The value must be a directory name and can be given in either standard
291    syntax (including the possibility that it is itself an anchored path)
292    or native syntax.
293    
294    Examples:
295    
296       foo.cm (bind:(anchor:bar value:$mystuff/bar))
297       lib.cm (bind:(anchor:a value:"H:\\x\\y\\z"))  (* only works under windows *)
298    
299    and so on.
300    
301    The meaning of this is that the .cm-file will be processed with an
302    augmented anchor environment where the given anchor(s) is/are bound to
303    the given values(s).
304    
305    The rationale for having this feature is this: Suppose you are trying
306    to use two different (already stable) libraries a.cm and b.cm (that
307    you perhaps didn't write yourself).  Further, suppose each of these
308    two libraries internally uses its own auxiliary library $aux/lib.cm.
309    Normally you would now have a problem because the anchor "lib" can not
310    be bound to more than one value globally.  Therefore, the project that
311    uses both a.cm and b.cm must locally redirect the anchor to some other
312    place:
313    
314       a.cm (bind:(anchor:lib value:/usr/lib/smlnj/a-stuff))
315       b.cm (bind:(anchor:lib value:/usr/lib/smlnj/b-stuff))
316    
317    This hard-wires $lib/aux.cm to /usr/lib/smlnj/a-stuff/aux.cm or
318    /usr/lib/smlnj/b-stuff/aux.cm, respectively.
319    
320    Hard-wiring path names is a bit inflexible (and CM will verbosely warn
321    you when you do so at the time of CM.stabilize).  Therefore, you can
322    also use an anchored path as the value:
323    
324      a.cm (bind:(anchor:lib value:$a-lib))
325      b.cm (bind:(anchor:lib value:$b-lib))
326    
327    Now you can globally configure (using the usual CM.Anchor.anchor or
328    pathconfig machinery) bindings for "a-lib" and "b-lib".  Since "lib"
329    itself is always locally bound, setting it globally is no longer
330    meaningful or necessary (but it does not hurt either).  In fact, "lib"
331    can still be used as a global anchor for separate purposes.  As a
332    matter of fact, one can locally define "lib" in terms of a global
333    "lib":
334    
335      a.cm (bind:(anchor:lib value:$lib/a))
336      b.cm (bind:(anchor:lib value:$lib/b))
337    
338    ** 3: The encoding of path names has changed.  This affects the way
339    path names are shown in CM's progress report and also the internal
340    protocol encoding used for parallel make.
341    
342    The encoding now uses one or more ':'-separated segments.  Each
343    segments corresponds to a file that has been specified relative to the
344    file given by its preceding segment.  The first segment is either
345    relative to the CWD, absolute, or anchored.  Each segment itself is
346    basically a Unix pathname; all segments but the first are relative.
347    
348    Example:
349    
350       $foo/bar/baz.cm:a/b/c.sml
351    
352    This path denotes the file bar/a/b/c.sml relative to the directory
353    denoted by anchor "foo".  Notice that the encoding also includes
354    baz.cm which is the .cm-file that listed a/b/c.sml.  As usual, such
355    paths are resolved relative to the .cm-files directory, so baz.cm must
356    be ignored to get the "real" pathname.
357    
358    To make this fact more obvious, CM puts the names of such "virtual
359    arcs" into parentheses when they appear in progress reports. (No
360    parentheses will appear in the internal protocol encoding.)  Thus,
361    what you really see is:
362    
363      $foo/bar/(baz.cm):a/b/c.sml
364    
365    I find this notation to be much more informative than before.
366    
367    Another new feature of the encoding is that special characters
368    including parentheses, colons, (back)slashes, and white space are
369    written as \ddd (where ddd is the decimal encoding of the character).
370    
371    *** The CM manual still needs to be updated.
372    
373    ----------------------------------------------------------------------
374  Name: Allen Leung  Name: Allen Leung
375  Date: 2000/06/15 00:38:00  Date: 2000/06/15 00:38:00
376  Tag: leunga-20000615-x86-peephole  Tag: leunga-20000615-x86-peephole

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