[Caml-list] Seg fault with -custom and 2049 lets...

[Caml-list] Seg fault with -custom and 2049 lets...

[David Fox]

If I create a program with 2049 simple functions:

  let f1 () = ()
  let f2 () = ()
  ...
  let f2049 () = ()

(You can build this using yes "" | cat -n | head -2049 |
 sed 's/^[^0-9]*\([0-9]*\)[^0-9]*$/let f\1 () = ()/' > y.ml)

I get a seg fault if I compile it with the -custom flag and use a
debugging version of malloc:

  % ocamlc -custom y.ml -ccopt -lefence
  % ./a.out
  
   Electric Fence 2.2.0 Copyright (C) 1987-1999 Bruce Perens <bruce@perens.com>
  Segmentation fault (core dumped)
  % 

or if I link using the debugging library libcamlrund.a:

  % ./a.out
  ### O'Caml runtime: debug mode ###
  Initial minor heap size: 128k bytes
  Initial major heap size: 248k bytes
  Initial space overhead: 42%
  Initial max overhead: 1000000%
  Initial heap increment: 248k bytes
  Initial stack limit: 1024k bytes
  file interp.c; line 255 ### Assertion failed: sp >= stack_low

If I use the regular (non-debugging) library I don't get the seg fault
immediately, but in a real life situation things get ugly pretty
quickly.

-david
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Re: [Caml-list] Seg fault with -custom and 2049 lets...

[David Fox]

By the way, this was on a Pentium 3 machine running Redhat Linux 7.0
and ocaml-3.01.

David Fox <dsfox@COGSCI.ucsd.edu> writes:

> If I create a program with 2049 simple functions:
> 
>   let f1 () = ()
>   let f2 () = ()
>   ...
>   let f2049 () = ()
> 
> (You can build this using yes "" | cat -n | head -2049 |
>  sed 's/^[^0-9]*\([0-9]*\)[^0-9]*$/let f\1 () = ()/' > y.ml)
> 
> I get a seg fault if I compile it with the -custom flag and use a
> debugging version of malloc:
> 
>   % ocamlc -custom y.ml -ccopt -lefence
>   % ./a.out
>   
>    Electric Fence 2.2.0 Copyright (C) 1987-1999 Bruce Perens <bruce@perens.com>
>   Segmentation fault (core dumped)
>   % 
> 
> or if I link using the debugging library libcamlrund.a:
> 
>   % ./a.out
>   ### O'Caml runtime: debug mode ###
>   Initial minor heap size: 128k bytes
>   Initial major heap size: 248k bytes
>   Initial space overhead: 42%
>   Initial max overhead: 1000000%
>   Initial heap increment: 248k bytes
>   Initial stack limit: 1024k bytes
>   file interp.c; line 255 ### Assertion failed: sp >= stack_low
> 
> If I use the regular (non-debugging) library I don't get the seg fault
> immediately, but in a real life situation things get ugly pretty
> quickly.
> 
> -david
> -------------------
> To unsubscribe, mail caml-list-request@inria.fr.  Archives: http://caml.inria.fr
> 

-- 
$_='while(read+STDIN,$_,2048){$a=29;$b=73;$c=142;$t=255;@t=map{$_%16or$t^=$c^=(
$m=(11,10,116,100,11,122,20,100)[$_/16%8])&110;$t^=(72,@z=(64,72,$a^=12*($_%16
-2?0:$m&17)),$b^=$_%64?12:0,@z)[$_%8]}(16..271);if((@a=unx"C*",$_)[20]&48){$h
=5;$_=unxb24,join"",@b=map{xB8,unxb8,chr($_^$a[--$h+84])}@ARGV;s/...$/1$&/;$
d=unxV,xb25,$_;$e=256|(ord$b[4])<<9|ord$b[3];$d=$d>>8^($f=$t&($d>>12^$d>>4^
$d^$d/8))<<17,$e=$e>>8^($t&($g=($q=$e>>14&7^$e)^$q*8^$q<<6))<<9,$_=$t[$_]^
(($h>>=8)+=$f+(~$g&$t))for@a[128..$#a]}print+x"C*",@a}';s/x/pack+/g;eval 
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[Caml-list] Just wasted half-an-hour on returned curried functions

[Mattias Waldau]

I removed the last int-argument of a function,
but only changed at the calls and in the
body, however not in the arguments, thus I had an unused arg
called ~(idx:int), i.e.

let bar a ~(idx:int) =
	{ var = a ; .... }

I created data using this function and these
(now curried) arguments were put into an array, and there is where I
got the type error. It took me 30 minutes to find the true source.

I could have found the error if I would have typed the result of the
above mentioned function either at the return value or in the let,
i.e. writing

let bar a ~(idx:int) :annotated_var =
	{ var = a ; .... }

or

let x:annotated_var = ..... in

However, the compiler could have found the error for immediately by
either

1. Told me that ~(idx:int) is an unused argument
2. or, had a special syntax ( for example '=()' ) for curried values, for
example,
   and by that immediately complain in the let above.

I know that alternative 2 is an absurd suggestion in the church of FPLs :-)
but I don't like wasting time. Could someone give me some example code
(except lablgtk, which is a nice but very hard to understand program)
where the majority of the returned values are functions.


/mattias

P.s. I don't understand how to get warning using ocamlc, for example in the
below code I both override methods and hide instance variables, but get no
warnings.

let foo () =
	let x = 0 in
	let x = 1 in
	x

let foo () =
	let x = 0 in
	let x = 1 in
	x

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Re: [Caml-list] Seg fault with -custom and 2049 lets...

[Xavier Leroy]

> If I create a program with 2049 simple functions:
> I get a seg fault if I compile it with the -custom flag and use a
> debugging version of malloc:
> or if I link using the debugging library libcamlrund.a:

Yes, this is a bug in the bytecode compiler causing the virtual
machine not to grow its stack enough to accommodate all the stack
slots that your declaration requires.  This will be fixed shortly.

- Xavier Leroy
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Re: [Caml-list] Seg fault with -custom and 2049 lets...

[David Fox]

Xavier Leroy <Xavier.Leroy@inria.fr> writes:

> > If I create a program with 2049 simple functions:
> > I get a seg fault if I compile it with the -custom flag and use a
> > debugging version of malloc:
> > or if I link using the debugging library libcamlrund.a:
> 
> Yes, this is a bug in the bytecode compiler causing the virtual
> machine not to grow its stack enough to accommodate all the stack
> slots that your declaration requires.  This will be fixed shortly.

I found a quick fix to get my X top level working:

--- ocaml-3.01/byterun/config.h~	Sun Oct 29 09:36:41 2000
+++ ocaml-3.01/byterun/config.h	Wed Apr 18 16:19:58 2001
@@ -76,7 +76,7 @@
 #define Page_log 12             /* A page is 4 kilobytes. */
 
 /* Initial size of stack (bytes). */
-#define Stack_size (4096 * sizeof(value))
+#define Stack_size (16384 * sizeof(value))
 
 /* Minimum free size of stack (bytes); below that, it is reallocated. */
 #define Stack_threshold (256 * sizeof(value))
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